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PubMed1983

Electrical activities of the muscle layers of the canine colon.

The spontaneous electrical and mechanical activities of the circular and longitudinal muscle layers of the canine colon were studied. The smooth muscle cells of the circular muscle layer exhibited regular, omni-present myogenic slow-wave activity at a frequency ranging from 4 to 7 c/min. With intracellular micro-electrodes, the slow-wave amplitude was 21-38 mV and its duration 3-6 sec. The 'resting' membrane potential was -60 to -76 mV. Some slow waves had superimposed spike bursts on their peak depolarizations and only these were associated with phasic contractions. It is concluded that they serve a pace-maker function similar to their counterpart in the small intestine. The longitudinal muscle layer exhibited periods of electrical activity alternating with periods of electrical quiescence. During the activity periods electrical oscillations occurred at a frequency of 13-35 c/min with spikes on top of them. Each electrical activity period was associated with a prolonged 'tonic' contraction. The duration of these periods was 30-120 sec and their frequency 0.4-1.1 period/min. This activity is similar to that recorded from the longitudinal muscle of the guinea-pig caecum despite the anatomical differences. The electrical activity periods of the longitudinal muscle appeared to require an excitatory input (stretch and/or acetylcholine release). Provided the strips were not excessively stretched, atropine abolished all electrical and motor activity. Stretching prolonged the electrical activity periods until they eventually fused together and the muscle developed maintained tone. Simultaneously recording from both layers showed that, although electrotonic spread between the two layers is probably insignificant, the activity of the two layers was co-ordinated. Only those slow waves of the circular layer that occurred during the electrical activity periods of the longitudinal layer had superimposed spikes. It is suggested that this co-ordination may indicate that the two muscle layers may be commanded by a common input from periodically active, cholinergic intramural neurones. It is proposed that the complex patterns of colonic electrical and motor activities may be explained as consisting of two major components: one arising from the longitudinal (long spike bursts, high-frequency oscillations and tonic contractions) and the other from the circular layer (slow waves, short spike and phasic contractions). Simultaneous electrical records from the two muscle layers and the mucosa failed to show a consistent relationship between the mucosal record and the activity of either layer. Caution should be exercised in the interpretation of intraluminally derived electrical recordings.

Action Potentials↗
PubMed1987

Electrical control activity of the lower esophageal sphincter in unanesthetized opossums.

We recorded lower esophageal sphincter (LES) pressure and myoelectrical activity concurrently from the esophagus, LES, stomach, and proximal small intestine in unanesthetized opossums. LES electrical activity was characterized by almost continuous, spikelike oscillations at 15-40/min, which were accompanied by minicontractions 5-15 mmHg in amplitude. Basal LES pressure, however, did not depend on electrical oscillations. The LES exhibited cyclic changes in pressure and electrical activity synchronous with gastric contractions associated with the migrating myoelectric complex (MMC). During phase I, the LES pressure was stable and its electrical activity showed continuous low-amplitude (less than 0.3 mV) oscillations at a rate of 20 +/- 2 per min. During phases II and III of MMC-related gastric activity, the LES developed strong phasic contractions, while the electrical oscillations grouped into clusters with an increased rate (32 +/- 1 per min) and amplitude (0.4-0.8 mV), each cluster corresponding to a phasic contraction. Feeding, pentobarbital, and cholinergic blockade abolished MMC-related LES activity and resulted in a steady rate of LES electrical oscillations. LES relaxation induced by swallows or esophageal balloon distention abolished the LES electrical oscillations. Increases in LES pressure induced by pharmacological and hormonal stimulation correlated with concurrent increases in the rate of electrical oscillations. We conclude that the opossum LES has a unique pattern of electrical activity that differs from the electrical activity recorded from smooth muscle elsewhere in the gastrointestinal tract. This electrical activity is a form of control wave associated with a minicontraction. Phasic LES contractions during the intestinal MMC cycle may result from an increase in the rate and amplitude of the LES electrical control waves and fusion of minicontractions.

Anesthesia↗
PubMed1999

Active electrolocation of objects in weakly electric fish

Weakly electric fish produce electric signals (electric organ discharges, EODs) with a specialised electric organ creating an electric field around their body. Objects within this field alter the EOD-induced current at epidermal electroreceptor organs, which are distributed over almost the entire body surface. The detection, localisation and analysis of objects performed by monitoring self-produced electric signals is called active electrolocation. Electric fish employ active electrolocation to detect objects that are less than 12 cm away and have electric properties that are different from those of the surrounding water. Within this range, the mormyrid Gnathonemus petersii can also perceive the distance of objects. Depth perception is independent of object parameters such as size, shape and material. The mechanism for distance determination through electrolocation involves calculating the ratio between two parameters of the electric image that the object projects onto the fish's skin. Electric fish can not only locate objects but can also analyse their electrical properties. Fish are informed about object impedance by measuring local amplitude changes at their receptor organs evoked by an object. In addition, all electric fish studied so far can independently determine the capacitative and resistive components of objects that possess complex impedances. This ability allows the fish to discriminate between living and non-living matter, because capacitance is a property of living organisms. African mormyrids and South American gymnotiforms use different mechanisms for capacitance detection. Mormyrids detect capacitance-evoked EOD waveform distortions, whereas gymnotiforms perform time measurements. Gymnotiforms measure the temporal phase shift of their EODs induced at body parts close to the object relative to unaffected body parts further away.

Journal Article↗
PubMed1996

Isolated, electrically-stimulated airway preparations--their use in determining beta-adrenoceptor agonist activity.

We have assessed the suitability of electrically-stimulated superfused preparations of guinea-pig trachea, cat trachea and human bronchus for investigating the relaxant activity of the beta-adrenoceptor agonist, isoprenaline. Superfused strips of guinea-pig trachea, cat trachea and human bronchus all contracted in response to electrical stimulation. Guinea-pig trachea possesses inherent tone, and in its presence, electrical stimulation caused biphasic responses, comprising a modest, transient contraction, usually followed by a longer lasting relaxation. Human bronchus also possesses inherent tone, but responses were variable, generally monophasic, comprising a transient contraction of variable magnitude, but a longer lasting relaxation was occasionally observed after the transient contraction. Cat trachea possesses no inherent tone, and electrical stimulation of this preparation caused simple monophasic contractile responses. On guinea-pig trachea, addition of indomethacin (2.8 microM) abolished the inherent tone, and under these conditions, electrical stimulation caused monophasic contractile responses similar to those observed in cat trachea. On human bronchus, however, indomethacin enhanced inherent tone, which tended to uncover or exaggerate any relaxant component in the responses to electrical stimulation. The 5-lipoxygenase inhibitor, zileuton (10 microM), reduced, but did not abolish, the tone and converted the electrically-induced response to a monophasic contraction. In all preparations in which inherent tone was low or absent, whether naturally (cat trachea) or through pharmacological intervention (guinea-pig trachea with indomethacin, or human bronchus with zileuton), isoprenaline (1-100 nM) inhibited electrically-stimulated contractions in a concentration-related fashion (EC50s: 9-100 nM). In preparations exhibiting inherent tone (guinea-pig trachea with indomethacin or human bronchus with or without indomethacin), this tone was inhibited by isoprenaline. This relaxant activity, on guinea-pig trachea at least, was concentration-related (EC50: 5.4 nM). Such isoprenaline-induced relaxations complicated the analysis of inhibitory effects against electrically-induced contractions. Thus, in such experiments, only at higher concentrations did isoprenaline reliably inhibit these contractions (EC50: 23-119 nM), lower concentrations of isoprenaline often resulting in an apparent enhancement. The enhancement was probably artefactual, resulting from the fact that the electrically-induced contractions originated from a lower baseline. These data suggest that electrically-stimulated airway preparations are suitable for evaluating the relaxant activity of beta-adrenoceptor agonists, but the relaxant potency should be assessed in preparations lacking inherent tone, such as cat trachea, guinea-pig trachea in the presence of cyclo-oxygenase inhibition, or human bronchus in the presence of 5-lipoxygenase inhibition.

Adrenergic beta-2 Receptor Agonists↗
PubMed1976

Electrical hemolysis of human and bovine red blood cells.

The external electric field strength required for electrical hemolysis of human red blood cells depends sensitively on the composition of the external medium. In isotonic NaCl und KCl solutions the onset of electrical hemolysis is observed at 4 kV per cm and 50 per cent hemolysis at 6 kV per cm, whereas increasing concentrations of phosphate, sulphate, sucrose, inulin and EDTA shift the onset and the 50 per cent hemolysis-value to higher field strengths. The most pronounced effect is observed for inulin and EDTA. In the presence of these substances the threshold value of the electric field strength is shifted to 14 kV per cm. This is in contrast to the dielectric breakdown voltage of human red blood cells which is unaltered by these substances and was measured to be approximately 1 V corresponding in the electrolytical discharge chamber to an external electric field strength of 2 to 3 kV per cm. On the other hand, dielectric breakdown of bovine red blood cell membranes occurs in NaCl solution at 4 to 5 kV per cm and is coupled directly with hemoglobin release. The electrical hemolysis of cells of this species is unaffected by the above substances with exception of inulin. Inulin suppressed the electrical hemolysis up to 15 kV per cm. The data can be explained by the assumption that the reflection coefficients of the membranes of these two species to bivalent anions and uncharged molecules are field-dependent to a different extent. This explanation implies that electrical hemolysis is a secondary process of osmotic nature induced by the reversible permeability change of the membrane (dielectric breakdown) in response to an electric field. This view is supported by the observation that the mean volumes of ghost cells obtained by electrical hemolysis can be changed by changing the external phosphate concentration during hemolysis and resealing, or by subjecting the cells to a transient osmotic stress immediately after the electrical hemolysis step. An interesting finding is that the breakdown voltage, although constant throughout each normally distributed ghost size distribution, increases with increasing mean volume of the ghost populations.

Animals↗
PubMed2006

Stress relaxation in porcine septal cartilage during electromechanical reshaping: mechanical and electrical responses.

Electromechanical reshaping (EMR) of facial cartilage has recently been developed as an alternative to classic surgical techniques to alter cartilage shape. This study focuses on determining the underlying physical mechanisms responsible for shape change (stress relaxation) in mechanically deformed facial cartilage specimens exposed to constant electric fields. Flat porcine nasal septal cartilage specimens were deformed by an aluminum jig into semicylindrical shapes while a constant electric voltage was applied to the concave and convex surfaces of the specimen. Mechanical stress, electric current and resistance were measured during voltage application. Specimen shape retention was measured as retained bend angle. Total electric charge transferred in the electric circuit was calculated from the electric current measurement. Electrical resistance, transferred charge and the bend angle increase with increase in voltage application time until bend angle reaches maximum value determined by the jig geometry. Then, the bend angle decreases and electrical parameters nearly saturate. The time dependent behavior of electric current was analyzed using the Cottrell equation. The observed changes in electric current suggest that during the initial 1-2 min of EMR nonlinear diffusion determines electro-chemical reaction rates, which are then followed by a linear diffusion dominated process. Close correlation between alteration of cartilage mechanical state and change in its electrical properties suggest that an electro-chemical reaction is the dominant mechanism behind EMR.

Animals↗
PubMed1998

A1 adenosine receptor modulation of electrically-evoked contractions in the bisected vas deferens and cauda epididymis of the guinea-pig.

1. The effects of adenosine receptor agonists upon both electrically-evoked and phenylephrine-induced contractile responses were investigated in the bisected vas deferens and the cauda epididymis of the guinea-pig. Electrical field-stimulation (10 s trains of pulses at 9 Hz, 0.1 ms duration, supramaximal voltage) elicited biphasic and monophasic contractile responses from preparations of bisected vas deferens and cauda epididymis, respectively; these responses were abolished by tetrodotoxin (300 nM). 2. In the prostatic half of the vas deferens the A1 selective adenosine receptor agonists, N6-cyclopentyladenosine (CPA) and (2S)-N6-[2-endo-norbornyl]adenosine ((S)-ENBA) and the non-selective A1/A2 adenosine receptor agonist, 5'-N-ethylcarboxamidoadenosine (NECA) inhibited electrically-evoked contractions (pIC50+/-s.e.mean values 6.15+/-0.24, 5.99+/-0.26 and 5.51+/-0.24, respectively). The responses to CPA were blocked by the A1 adenosine receptor antagonist, 8-cyclopentyl-1,3-dipropylxanthine, DPCPX (100 nM). 3. In the epididymal half of the vas deferens NECA potentiated (at < or = 100 nM) and inhibited (at > or = 1 microM) electrically-evoked contractions. In the presence of the non-selective alpha-adrenoceptor antagonist phentolamine (3 microM), the alpha1-adrenoceptor antagonist, prazosin (100 nM), or at a reduced train length (3 s) NECA inhibited electrically-evoked contractions (pIC50 values 6.05+/-0.25, 5.97+/-0.29 and 5.71 +/-0.27, respectively). CPA (at 10 microM) also inhibited electrically-evoked contractions in this half of the vas deferens. In the presence of prazosin (100 nM), CPA also inhibited electrically-evoked contractions (pIC50 6.14+/-0.67); this effect was antagonized by DPCPX (30 nM, apparent pK(B) 8.26+/-0.88). In the presence of the P2 purinoceptor antagonist, suramin (300 microM), CPA (up to 1 microM) potentiated electrically-evoked contractions. 4. NECA, CPA and APNEA potentiated electrically-evoked contractions in preparations of cauda epididymis (pEC50 values 7.49+/-0.62, 7.65+/-0.74 and 5.84+/-0.86, respectively), the response to CPA was competitively antagonized by DPCPX (100 nM) with an apparent pK(B) value of 7.64+/-0.64. 5. The alpha1-adrenoceptor agonist phenylephrine elicited concentration-dependent contractile responses from preparations of bisected vas deferens and cauda epididymis. NECA (1 microM) potentiated responses to phenylephrine (< or = 1 microM) in the epididymal, but not in the prostatic half of the vas deferens. In preparations of epididymis NECA (1 microM) shifted phenylephrine concentration response curves to the left (4.6 fold). In the presence of a fixed concentration of phenylephrine (1 microM), NECA elicited concentration-dependent contractions of preparations of the epididymal half of the vas deferens and of the epididymis (pEC50 values 7.57+/-0.54 and 8.08+/-0.18, respectively). NECA did not potentiate responses to ATP in either the epididymal half of the vas deferens or the epididymis. 6. These studies are consistent with the action of stable adenosine analogues at prejunctional A1 and postjunctional A1-like adenosine receptors. The prejunctional A1 adenosine receptors only inhibit the electrically-evoked contractions of purinergic origin (an effect predominant in the prostatic half of the vas deferens). At the epididymis, where electrically-evoked contractions are entirely adrenergic, the predominant adenosine receptor agonist effect is a potentiation of alpha1-adrenoceptor-, but not of ATP-induced contractility.

Adenosine Triphosphate↗
PubMedDate not supplied

Effect of electrical stimulation on chronic wound healing: a meta-analysis.

The purpose of this meta-analysis was to quantify the effect of electrical stimulation on chronic wound healing. Fifteen studies, which included 24 electrical stimulation samples and 15 control samples, were analyzed. The average rate of healing per week was calculated for the electrical stimulation and control samples. Ninety-five percentage confidence intervals were also calculated. The samples were then grouped by type of electrical stimulation device and chronic wound and reanalyzed. Rate of healing per week was 22% for electrical stimulation samples and 9% for control samples. The net effect of electrical stimulation was 13% per week, an increase of 144% over the control rate. The 95% confidence intervals of the electrical stimulation (18-26%) and control samples (3.8-14%) did not overlap. Electrical stimulation was most effective on pressure ulcers (net effect = 13%). Findings regarding the relative effectiveness of different types of electrical stimulation device were inconclusive. Although electrical stimulation produces a substantial improvement in the healing of chronic wounds, further research is needed to identify which electrical stimulation devices are most effective and which wounds respond best to this treatment.

Electric Stimulation Therapy↗
PubMed1996

Reorganization of microfilament structure induced by ac electric fields.

AC electric fields induce redistribution of integral membrane proteins. Cell-surface receptor redistribution does not consistently follow electric field lines and depends critically on the frequency of the applied ac electric fields, suggesting that mechanisms other than electroosmosis are involved. We hypothesized that cytoskeletal reorganization is responsible for electric field-induced cell-surface receptor redistribution, and used fluorescence video microscopy to study the reorganization of microfilaments in human hepatoma (Hep3B) cells exposed to low-frequency electric fields ranging in strength from 25 mV/cm to 20 V/cm (peak to peak). The frequency of the applied electric field was varied from 1 to 120 Hz and the field exposure duration from 1 to 60 min. In control cells, cytoplasmic microfilaments were aligned in the form of continuous parallel cables along the longitudinal axis of the cell. Exposure of cells to ac electric fields induced alterations in microfilament structure in a manner that depended on the frequency of the applied field. A 1 or 10 Hz ac field caused microfilament reorganization from continuous, aligned cable structures to discontinuous globular patches. In contrast, the structure of microfilaments in cells exposed to 20-120 Hz electric fields did not differ from that in control cells. The extent of microfilament reorganization increased nonlinearly with the electric field strength. The characteristic time for microfilament reorganization in cells exposed to a 1 Hz, 20 V/cm electric field was approximately 5 min. Applied ac electric fields could initiate signal transduction cascades, which in turn cause reorganization of cytoskeletal structures.

Actin Cytoskeleton↗
PubMed2005

Electrical impedance scanning for melanoma diagnosis: a validation study.

BACKGROUND: A multicenter study was conducted to test the ability of electrical impedance scanning to differentiate between benign and malignant skin lesions. The performance of a dual electrical impedance scanning/image analysis device was also assessed. METHODS: Electrical impedance scanning measurements of 449 preoperative lesions found on 382 patients and including 53 melanomas from the trunk and extremities were performed. Results were correlated with histopathologic findings. In addition, ABCD parameters for the lesions were automatically calculated by the system. RESULTS: Electrical impedance scanning detected melanomas of the trunk and extremities with 91 percent sensitivity and 64 percent specificity. Moreover, sensitivity of electrical impedance scanning was increased to 100 percent for in situ and thin melanomas of smaller size (n = 27). Visual examination identified as malignant only 67 percent of these early tumors (p = 0.002). Clinical examination detected 96 percent of the larger or thicker melanomas (n = 26), whereas electrical impedance scanning detected only 81 percent of them. Combined electrical impedance scanning and image analysis detected 100 percent of the melanomas, independent of their thickness, and with no significant decrease of specificity. Because of electrical differences between the head/neck and the rest of the body, the assessed electrical impedance scanning parameters were not adequate for the diagnosis of melanomas from the head and neck. CONCLUSIONS: A validation study proved the value of electrical impedance scanning as a noninvasive technique for detection of melanoma lesions of the trunk and extremities, specifically, of in situ and thin type. In addition, image analysis was shown to be a valuable, complementary procedure. New parameters should be designed to optimize the performance of electrical impedance scanning for melanomas of the head and neck.

Adult↗
PubMed1999

Bidirectional transfer between electrical and flurothyl kindling in mice: evidence for common processes in epileptogenesis.

PURPOSE: This study sought to determine whether there was a transfer of seizure susceptibility between two models of epileptogenesis, electrical kindling and a newly described model of flurothyl kindling. In this study, we determined the effects of preexposure to one kindling agent on the seizure responsiveness to the other. METHODS: Mice were divided into three groups: (a) six mice (FLK) were kindled with flurothyl, rechallenged with flurothyl after a 28-day incubation phase, implanted with olfactory bulb (OB) electrodes, and electrically kindled; (b) six mice (ELK) were implanted with OB electrodes, electrically kindled to six stage 5 seizures, and given one flurothyl trial 3 days later and a second flurothyl trial after a 28-day incubation period; and (c) six mice (IMP) were implanted with OB electrodes, tested with flurothyl at the same times as the ELK group, and later electrically kindled. RESULTS: Mice that were previously kindled with flurothyl (FLK) had significantly faster electrical kindling rates to one stage 5 seizure or to six stage 5 seizures compared with animals in the ELK and IMP groups. Mice that were previously exposed to either electrical kindling or flurothyl kindling had significantly diminished latencies to generalized seizure onset (flurothyl-induced seizure thresholds) either before or after a 28-day incubation period compared with the IMP control mice. In addition, both the FLK and ELK groups had significantly increased percentages of mice expressing forebrain-brainstem seizures, compared with the IMP group, following either rechallenge with flurothyl after a 28-day incubation or focal electrical kindling. CONCLUSIONS: These findings indicate a near-complete bidirectional transfer between these electrical and flurothyl kindling models. Mice that were previously exposed to either electrical or flurothyl kindling have increased seizure susceptibilities and altered seizure phenotypes when exposed to the other seizure paradigm. Overall, these studies indicate that previous seizures are the critical determinant of the bidirectional transfer of seizure susceptibility observed, and not the electrical or pharmacologic properties of the original kindling agent. Finally, the observation of near identity in transfer characteristics between electrical and flurothyl kindling models suggests that the proepileptogenic processes initiated by exposure to either model are similar.

Animals↗
PubMed1981

The development of electrical properties of identified neurones in grasshopper embryos.

1. We have examined the development of the electrical properties of five identified neurones in grasshopper embryos between days 10 and 13 of embryogenesis (hatching occurs on day 20). DUM 3,4,5; DUM 4,5; DUM 5; the H cell; and the H cell sibling are the progeny of two different precursor cells. Electrical coupling and electrical excitability were assayed by intracellular recordings. 2. Midway through embryogenesis, on day 10, the five cells are highly electrically coupled to each other and are electrically inexcitable. The temporal sequence of the development of electrical excitability and electrical coupling is described for DUM 3,4,5; 4,5; and 5. The H cell and H cell sib undergo the same sequence one day later. 3. The first non-linear membrane property to appear is delayed rectification which appears on day 11 and can be blocked by tetraethylammonium (TEA). In some cells at about day 11, the addition of TEA to normal saline unmasks a Na+-dependent action potential in the axon. 4. The first action potential in normal saline is a Na+-dependent response that appears in the axon at day 11-11.5. 5. The next stage of excitability in normal saline is the appearance about day 11.5 of a Na+-dependent action potential in the median neurite between the soma and the two axons. In some cells at about day 11.5, the addition of TEA unmasks an excitable response in the soma. 6. Overshooting action potentials appear in the soma about day 12; the inward current is carried by both Na+ and Ca2+; TEA causes a prolonged shoulder on the falling phase of the action potential. A short time later, TEA causes a long-duration CA2+ plateau. 7. A progressive decrease in the degree of electrical coupling among the cells occurs between days 10 and 12.5. Complete uncoupling is never observed before day 11, but has always occurred by day 12.5. 8. Two methods were used to demonstrate that electrical coupling does not mask the presence of excitable inward current channels and thus make the cells appear inexcitable. First, we exposed the cells to veratridine. The cells which normally generate excitable Na+ response are depolarized by it; the younger inexcitable cells are not. Secondly, we electrically isolated the cells by killing the somata of their neighbours. The input resistance increased, yet the extent of excitability remained unchanged. 9. There is variability in the precise temporal relationship of excitability and uncoupling. Pairs of cells from different embryos of the same ate can generate the same type of action potentials and yet be coupled in one embryo and uncoupled in another. Electrical excitability and uncoupling appear to be causally unrelated and independent events, occurring at about the same developmental stage.

Action Potentials↗
PubMed2005

Radiofrequency ablation: importance of background tissue electrical conductivity--an agar phantom and computer modeling study.

PURPOSE: To determine whether radiofrequency (RF)-induced heating can be correlated with background electrical conductivity in a controlled experimental phantom environment mimicking different background tissue electrical conductivities and to determine the potential electrical and physical basis for such a correlation by using computer modeling. MATERIALS AND METHODS: The effect of background tissue electrical conductivity on RF-induced heating was studied in a controlled system of 80 two-compartment agar phantoms (with inner wells of 0.3%, 1.0%, or 36.0% NaCl) with background conductivity that varied from 0.6% to 5.0% NaCl. Mathematical modeling of the relationship between electrical conductivity and temperatures 2 cm from the electrode (T2cm) was performed. Next, computer simulation of RF heating by using two-dimensional finite-element analysis (ETherm) was performed with parameters selected to approximate the agar phantoms. Resultant heating, in terms of both the T2cm and the distance of defined thermal isotherms from the electrode surface, was calculated and compared with the phantom data. Additionally, electrical and thermal profiles were determined by using the computer modeling data and correlated by using linear regression analysis. RESULTS: For each inner compartment NaCl concentration, a negative exponential relationship was established between increased background NaCl concentration and the T2cm (R2= 0.64-0.78). Similar negative exponential relationships (r2 > 0.97%) were observed for the computer modeling. Correlation values (R2) between the computer and experimental data were 0.9, 0.9, and 0.55 for the 0.3%, 1.0%, and 36.0% inner NaCl concentrations, respectively. Plotting of the electrical field generated around the RF electrode identified the potential for a dramatic local change in electrical field distribution (ie, a second electrical peak ["E-peak"]) occurring at the interface between the two compartments of varied electrical background conductivity. Linear correlations between the E-peak and heating at T2cm (R2= 0.98-1.00) and the 50 degrees C isotherm (R2= 0.99-1.00) were established. CONCLUSION: These results demonstrate the strong relationship between background tissue conductivity and RF heating and further explain electrical phenomena that occur in a two-compartment system.

Agar↗
PubMed2004

Antitumor effectiveness of different amounts of electrical charge in Ehrlich and fibrosarcoma Sa-37 tumors.

BACKGROUND: In vivo studies were conducted to quantify the effectiveness of low-level direct electric current for different amounts of electrical charge and the survival rate in fibrosarcoma Sa-37 and Ehrlich tumors, also the effect of direct electric in Ehrlich tumor was evaluate through the measurements of tumor volume and the peritumoral and tumoral findings. METHODS: BALB/c male mice, 7-8 week old and 20-22 g weight were used. Ehrlich and fibrosarcoma Sa-37 cell lines, growing in BALB/c mice. Solid and subcutaneous Ehrlich and fibrosarcoma Sa-37 tumors, located dorsolaterally in animals, were initiated by the inoculation of 5 x 10(6) and 1 x 10(5) viable tumor cells, respectively. For each type of tumor four groups (one control group and three treated groups) consisting of 10 mice randomly divided were formed. When the tumors reached approximately 0.5 cm3, four platinum electrodes were inserted into their bases. The electric charge delivered to the tumors was varied in the range of 5.5 to 110 C/cm3 for a constant time of 45 minutes. An additional experiment was performed in BALB/c male mice bearing Ehrlich tumor to examine from a histolological point of view the effects of direct electric current. A control group and a treated group with 77 C/cm3 (27.0 C in 0.35 cm3) and 10 mA for 45 min were formed. In this experiment when the tumor volumes reached 0.35 cm3, two anodes and two cathodes were inserted into the base perpendicular to the tumor long axis. RESULTS: Significant tumor growth delay and survival rate were achieved after electrotherapy and both were dependent on direct electric current intensity, being more marked in fibrosarcoma Sa-37 tumor. Complete regressions for fibrosarcoma Sa-37 and Ehrlich tumors were observed for electrical charges of 80 and 92 C/cm3, respectively. Histopathological and peritumoral findings in Ehrlich tumor revealed in the treated group marked tumor necrosis, vascular congestion, peritumoral neutrophil infiltration, an acute inflammatory response, and a moderate peritumoral monocyte infiltration. The morphologic pattern of necrotic cell mass after direct electric current treatment is the coagulative necrosis. These findings were not observed in any of the untreated tumors. CONCLUSION: The data presented indicate that electrotherapy with low-level DEC is feasible and effective in the treatment of the Ehrlich and fibrosarcoma Sa-37 tumors. Our results demonstrate that the sensitivity of these tumors to direct electric current and survival rates of the mice depended on both the amount of electrical charge and the type of tumor. Also the complete regression of each type of tumor is obtained for a threshold amount of electrical charge.

Animals↗
PubMed1990

[Electrical cardioversion after quinidine administration].

The aim of the present study was to investigate the influence of quinidine on the effectiveness of electrical cardioversion (CV) for the reversion of supraventricular arrhythmias, the amount of electrical energy necessary for the CV and the possible complications of electrical CV. Initially, 100 CV procedures were allocated to the control group (patients free from the action of any antiarrhythmic drug), and 50 CV to the quinidine group. Quinidine was given as dihydroquinidine C1H at a dose of 500 mg/12 hours since the day before CV. In the last group, 6 (12%) patients reverted to normal sinus rhythm before electrical CV. At the time of electrical CV (100 procedures in the control group and 44 in the quinidine group), the patients who received quinidine required a lower amount of electrical energy, and showed a lower incidence of atrial premature beats as compared with the control group (11.3% versus 28%, p less than 0.05). A similar proportion of patients reverted to sinus rhythm in both groups. We conclude that the administration of quinidine before electrical CV has the following advantages: 1) 12% of patients reverted to normal sinus rhythm before electrical CV; 2) quinidine reduced the amount of electrical energy necessary for the CV, and 3) quinidine reduced the incidence of atrial premature beats after electrical CV. On the other hand, quinidine had no influence on the incidence of ventricular arrhythmias after electrical CV.

Adult↗
PubMed1994

[Intracellular free calcium changes of mouse oocytes during activation induced by ethanol or electrical stimulations and parthenogenetic development].

Oocytes collected 18-19 h after HCG injection were stimulated with 7-8% ethanol or electrical pulses (1.7 KV/cm field strength, 80-100 microseconds duration, 3-4 times, 5-6 min interval). The parthenogenetic embryos derived from the above-mentioned methods developed to blastocyst stage just like those developed from fertilized eggs. Mouse oocytes were rather sensitive to ethanol stimulation. More than 95% of the treated oocytes were activated after stimulation of 7-8% ethanol for 5 min. Multiple electrical stimulations induced higher activation percentages of oocytes than only single electrical stimulation (71.5% vs. 63.6%). Intact oocytes were loaded with fluorescent Ca2+ indicator fura-2 and intracellular free calcium changes during artificial activation were measured by fluorescence detector. The results showed that ethanol could induce repetitive transient Ca2+ concentration increase in activated oocytes. Single electrical stimulation only induced single free calcium concentration elevation in oocyte while multiple electrical pulses could induce repetitive Ca2+ increase (each electrical pulse elicited the corresponding Ca2+ concentration peak). The pronuclei were not observed in the oocytes which had not exhibited calcium concentration rise during activation. Apart from electrical stimulation parameter, sufficient amount of Ca2+ in electric medium was crucial to mouse oocyte activation when stimulated with electrical pulses. The oocytes were hardly activated by electrical stimulations in a medium without Ca2+ even with longer pulse duration and the intracellular free calcium concentration in the oocytes showed no elevation. This indicates that the inflow of extracellular Ca2+ from tiny pores across the oocyte membrane caused by electrical stimulation is the main source of intracellular free calcium increase.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Mechanisms for electrical stimulation of excitable tissue.

Electric fields excite electrically active tissue by several mechanisms. A long, straight, uniform fiber is polarized by an activating function, proportional to the axial gradient of the axial electric field. During unipolar anodal stimulation, the activating function results in two areas of depolarization (virtual cathodes) that are responsible for anode-make stimulation. During unipolar cathodal stimulation, the virtual anodes can be exploited to produce unidirectional propagation and physiological recruitment of axons. Anode-break stimulation of nerves arises from the intrinsic properties of the sodium channel kinetics; cathode-break stimulation in nerves is anode-break stimulation at a virtual anode. The activating function applies to magnetic stimulation as well as to electric stimulation. Other important mechanisms of stimulation arise if the fiber is terminated, nonuniform, or curved. In the brain, cortical neurons are excited when the electric field is directed from the dendrites toward the axon. Possible mechanisms for cortical excitation are the impedance mismatch between the axon and dendritic tree, and the axon bending as it enters the white matter. Transcranial magnetic stimulation differs from transcranial electric stimulation because during magnetic stimulation the electric field is parallel to the brain surface, whereas during electric stimulation the electric field has components both parallel and perpendicular to the brain surface. Cardiac tissue can be represented by use of the bidomain model. This model predicts that a point-source stimulus results in adjacent areas of depolarized and hyperpolarized tissue. The presence of virtual anodes during cathodal stimulation is analogous to the creation of virtual anodes along a one-dimensional fiber by the activating function. Anode- and cathode-break stimulation both occur in cardiac tissue, but the mechanism may be different than for nerve and may depend on diffusion of depolarization into a previously hyperpolarized region. Electrical stimulation of cardiac tissue can cause reentry through a critical point mechanism. Two mechanisms for defibrillation have been hypothesized: (1) the relatively high junctional resistance between cardiac cells causes each cell to be depolarized on one side and hyperpolarized on the other; and (2) the fiber tracts within the heart behave like individual fibers, with fiber curvature providing a mechanism for polarization. Similarities among nerve, brain, and cardiac stimulation are emphasized.

Animals↗
PubMed2005

Ion channel clustering enhances weak electric field detection by neutrophils: apparent roles of SKF96365-sensitive cation channels and myeloperoxidase trafficking in cellular responses.

We have tested Galvanovskis and Sandblom's prediction that ion channel clustering enhances weak electric field detection by cells as well as how the elicited signals couple to metabolic alterations. Electric field application was timed to coincide with certain known intracellular chemical oscillators (phase-matched conditions). Polarized, but not spherical, neutrophils labeled with anti-K(v)1.3, FL-DHP, and anti-TRP1, but not anti-T-type Ca(2+) channels, displayed clusters at the lamellipodium. Resonance energy transfer experiments showed that these channel pairs were in close proximity. Dose-field sensitivity studies of channel blockers suggested that K(+) and Ca(2+) channels participate in field detection, as judged by enhanced oscillatory NAD(P)H amplitudes. Further studies suggested that K(+) channel blockers act by reducing the neutrophil's membrane potential. Mibefradil and SKF93635, which block T-type Ca(2+) channels and SOCs, respectively, affected field detection at appropriate doses. Microfluorometry and high-speed imaging of indo-1-labeled neutrophils was used to examine Ca(2+) signaling. Electric fields enhanced Ca(2+) spike amplitude and triggered formation of a second traveling Ca(2+) wave. Mibefradil blocked Ca(2+) spikes and waves. Although 10 microM SKF96365 mimicked mibefradil, 7 microM SKF96365 specifically inhibited electric field-induced Ca(2+) signals, suggesting that one SKF96365-senstive site is influenced by electric fields. Although cells remained morphologically polarized, ion channel clusters at the lamellipodium and electric field sensitivity were inhibited by methyl-beta-cyclodextrin. As a result of phase-matched electric field application in the presence of ion channel clusters, myeloperoxidase (MPO) was found to traffic to the cell surface. As MPO participates in high amplitude metabolic oscillations, this suggests a link between the signaling apparatus and metabolic changes. Furthermore, electric field effects could be blocked by MPO inhibition or removal while certain electric field effects were mimicked by the addition of MPO to untreated cells. Therefore, channel clustering plays an important role in electric field detection and downstream responses of morphologically polarized neutrophils. In addition to providing new mechanistic insights concerning electric field interactions with cells, our work suggests novel methods to remotely manipulate physiological pathways.

Animals↗