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PubMed2005

Peritoneal fast transport in incident peritoneal dialysis patients is not consistently associated with systemic inflammation.

BACKGROUND: The determinants of peritoneal fast transport status at the beginning of peritoneal dialysis (PD) are still under debate. The relationship between fast transport status and inflammation or co-morbidity, and its impact on patient survival are not fully elucidated. Our objective was to investigate if fast transport status in incident patients is associated with markers of inflammation and atherosclerosis, and its relationship to patient survival. METHODS: Seventy-three incident patients on PD performed a 3.86% peritoneal equilibrium test (PET) at 4.7+/-2.7 months after starting PD. Doppler carotid wall intima-media thickness (IMT) and the presence of carotid plaque were used as markers of atherosclerosis. C-reactive protein (CRP) and serum interleukin-6 (IL-6) were evaluated as markers of systemic inflammation. Baseline plasma levels of albumin, homocysteine, lipoprotein (a) [Lp(a)] and other lipid parameters were measured. Body mass index and residual renal function (RRF) were calculated. Patients were classified with the Davies co-morbidity score. RESULTS: The dialysate-plasma creatinine ratio (D/P creatinine) was 0.75 +/- 0.10; 26% were fast transporters (D/P > or = 0.85). In comparison with other transport categories, these had similar age, body mass index and RRF, and did not present a higher co-morbidity score than non-fast transporters. IMT did not significantly differ between groups. By multiple regression analysis, baseline peritoneal small solute transport was not related to systemic inflammation biomarkers. Fast transporters did not present higher levels of CRP or serum IL-6. Plasma levels of lipids, Lp(a), calcium x phosphorus product and albumin also did not differ between groups. Similar results were obtained when patients were grouped according to mass transfer area coefficient for creatinine. Patients with more than two co-morbidities had lower levels of plasma albumin (3.6 +/- 0.58 vs 3.9 +/- 0.9 g/dl, P = 0.054), significantly higher median levels of serum IL-6 (19.3 vs 9.2 pg/ml, P = 0.003) and wider IMT (0.90 +/- 0.36 vs 0.65 +/- 0.28 mm, P = 0.017). Multivariate analysis confirmed that baseline peritoneal transport was not a significant determinant of patient survival (P = 0.848), while the co-morbidity score remained significant (hazard ratio = 3.48, 95% confidence interval = 1.29-9.38, P = 0.014). CONCLUSION: Initial fast transport was not associated with systemic inflammation and atherosclerosis. In a population with preserved RRF and absence of baseline serious co-morbidity, it was not predictive of worse prognosis. Other determinants of early peritoneal fast transport deserve investigation.

Biological Transport↗
PubMedDate not supplied

Continuous enteral feeding and short fasting periods enhance perioperative nutrition in patients with burns.

Both retrospective and prospective analyses of the effects of various fasting regimens were carried out on the achievement of calculated caloric needs of patients with severe burns. The records of patients who received enteral feedings while undergoing burn debridements were divided into three groups and retrospectively analyzed to determine the effect that duration of fasting had an achievement of caloric needs and on the risks of aspiration. Patients in two other groups were prospectively studied to determine the safety and efficacy of stopping continuous enteral feedings 1 and 4 hours before surgery, respectively. Techniques of airway management and anesthetic induction were left to the discretion of the attending anesthesiologist. In the retrospective analysis, patients in group I, who fasted for 2 hours achieved 28% of their calculated 24-hour caloric goals compared with 11% in those who fasted for 2 to 8 hours (group II) and 6% in those who fasted for more than 8 hours (group III) before surgery (p less than 0.001). In the prospective portion of the study, patients who fasted for 1 hour before anesthesia was induced achieved 30% of their caloric needs, whereas those who fasted for 4 hours achieved 15% of their target nutritional needs (p = 0.0001). No patient had evidence of pulmonary aspiration. We conclude that controlled enteral feedings and shortened preoperative fasting periods can safely enhance nutritional support in patients with burns.

Adult↗
PubMed2000

Focused abdominal sonography for trauma (FAST) in children with blunt abdominal trauma.

BACKGROUND: Focused abdominal sonography for trauma (FAST) has been well reported in adults, but its applicability in children is less well established. We decided to test the hypothesis that FAST and computed tomography (CT) are equivalent imaging studies in the setting of pediatric blunt abdominal trauma. METHODS: One hundred seven hemodynamically stable children undergoing CT for blunt abdominal trauma were prospectively investigated using FAST. The ability of FAST to predict injury by detecting free intraperitoneal fluid was compared with CT as the imaging standard. RESULTS: Thirty-two patients had CT documented injuries. There were no late injuries missed by CT. FAST detected free fluid in 12 patients. Ten patients had solid organ injury but no free fluid and, thus, were not detected by FAST. The sensitivity of FAST relative to CT was only 0.55 and the negative predictive value was only 0.50. CONCLUSION: FAST has insufficient sensitivity and negative predictive value to be used as a screening imaging test in hemodynamically stable children with blunt abdominal trauma.

Abdominal Injuries↗
PubMed1994

Voltage dependencies of the fast and slow gating modes of RIIA sodium channels.

Rat brain IIA sodium channel alpha-subunits were expressed in Xenopus oocytes, and the sodium currents were measured by intracellular voltage clamping with large agarose-tipped electrodes and by excised membrane patch-clamp recording to separate and characterize the properties of the fast and slow channel gating modes. The currents showed biexponential inactivation properties with fast and slow phases that could be isolated as distinct gating modes through differences in their inactivation properties. At holding potentials more negative than -55 mV, fast mode currents inactivated within a few milliseconds of depolarization, and could be distinguished by their rapid recovery from inactivation. Single sodium channels in the fast mode opened early after depolarization and rarely showed re-openings. At holding potentials positive to -55 mV, fast mode currents were inactivated, revealing slow mode currents which had slower activation and inactivation kinetics and showed sustained single channel activity during depolarizing pulses. The steady-state voltage dependencies of fast and slow mode activation were very similar. In contrast, slow mode inactivation occurred at potentials 27 mV more positive than fast mode inactivation. The slow mode appears to be due to destabilization of a voltage-insensitive conformation of the channel. The fast gating process dominated at high current levels, perhaps due to alpha-subunit interactions.

Animals↗
PubMed1993

Coordinate changes in the expression of troponin subunit and myosin heavy-chain isoforms during fast-to-slow transition of low-frequency-stimulated rabbit muscle.

The purpose of this study was to follow the time course of changes in the expression of myosin heavy chain (HC) and troponin (Tn) subunit isoforms during fast-to-slow transition as induced in rabbit fast-twitch muscle by low-frequency stimulation. The evaluation of changes in the relative concentrations of myosin and troponin subunit isoforms were supplemented by measurements of relative protein synthesis rates using an in situ labeling technique. Changes in the amounts of mRNA encoding fast troponin C (TnC) were followed by Northern blot analysis, those for fast and slow troponin I (TnI) by in vitro translation of total RNA. The various fast myosin heavy chain (HC) and fast troponin T (TnT) isoforms were exchanged sequentially. Myosin HCIId which is the predominant fast isoform in rabbit tibialis anterior, was exchanged with HCIIa and, finally, the latter was replaced by the slow myosin HCI. The replacement of HCIId by HCIIa was accompanied by an exchange of TnT1f and TnT2f with TnT3f. The expression of HCI was accompanied by an exchange of TnT3f with the slow TnT isoforms, TnT1s and TnT2s. The changes in the relative concentrations of the TnT isoforms were preceded by similar changes of their relative synthesis rates. Pronounced decreases in the fast TnI and TnC isoforms occurred only with prolonged stimulation and were preceded by changes of the specific mRNAs and decreases in relative synthesis rates. The parallel time courses of the sequential transitions in both the myosin heavy chain and troponin T isoforms suggest the existence of coordinate programs of expression serving specific functional requirements.

Animals↗
PubMed2006

Convalescence after colonic surgery with fast-track vs conventional care.

OBJECTIVE: To compare convalescence after colonic surgery with a fast-track rehabilitation programme vs conventional care. BACKGROUND: Introduction of a multimodal rehabilitation programme (fast-track) with focus on epidural anaesthesia, minimal invasive surgical techniques, optimal pain control, and early nutrition and mobilization together with detailed patient information have led to a shorter hospital stay after colonic surgery. There are not much data on convalescence after discharge. METHODS: A prospective, controlled, non-randomized interview-based assessment in 160 patients undergoing an elective, uncomplicated, open colonic resection or the Hartmann reversal procedure with a fast-track or a conventional care programme in two university hospitals. A structured interview-based assessment was performed preoperatively, and day 14 and 30 postoperatively. RESULTS: Patients undergoing colonic surgery with a fast-track programme regained functional capabilities earlier with less fatigue and need for sleep compared with patients having conventional care. Despite early discharge of the fast-track patients (mean 3.4 days vs 7.5 days), no differences were found according to the need for home care, social care and visit to general practitioners, although the fast-track group had an increased number of visits at the outpatient clinic for wound care. More patients in the fast-track group were re-admitted, but the overall mean total hospital stay was 4.2 days vs 8.3 days in the conventional group. CONCLUSION: A fast-track rehabillitation programme led to a shorter hospital stay, less fatigue and earlier resumption of normal activities, without the increased need for support after discharge compared with conventionally treated patients after uncomplicated colonic resection.

Aged↗
PubMed2000

Prolonged depolarization promotes fast gating kinetics of L-type Ca2+ channels in mouse skeletal myotubes.

The effects of prolonged conditioning depolarizations on the activation kinetics of skeletal L-type calcium currents (L-currents) were characterized in mouse myotubes using the whole-cell patch clamp technique. The sum of two exponentials was required to adequately fit L-current activation and enabled determination of both the amplitudes (A(fast) and A(slow)) and time constants (tau(fast) and tau(slow)) of each component comprising the macroscopic current. Prepulses sufficient to activate (200 ms) or inactivate (10 s) L-channels did not alter tau(fast), tau(slow), or the fractional contribution of either the fast (A(fast)/(A(fast) + A(slow)) or slow (A(slow)/(A(fast) + A(slow))) amplitudes of subsequently activated L-currents. Prolonged depolarizations (60 s to +40 mV) resulted in the conversion of skeletal L-current to a fast gating mode following brief repriming intervals (3-10 s at -80 mV). Longer repriming intervals (30-60 s at -80 mV) restored L-channels to a predominantly slow gating mode. Accelerated L-currents originated from L-type calcium channels since they were completely blocked by a dihydropyridine antagonist (3 microM nifedipine) and exhibited a voltage dependence of activation similar to that observed in the absence of conditioning prepulses. The degree of L-current acceleration produced following prolonged depolarization was voltage dependent. For test potentials between +10 and +50 mV, the fractional contribution of Afast to the total current decreased exponentially with the test voltage (e-fold approximately 38 mV). Thus, L-current acceleration was most significant at more negative test potentials (e.g. +10 mV). Prolonged depolarization also accelerated L-currents recorded from myotubes derived from RyR1-knockout (dyspedic) mice. These results indicate that L-channel acceleration occurs even in the absence of RyR1, and is therefore likely to represent an intrinsic property of skeletal L-channels. The results describe a novel experimental protocol used to demonstrate that slowly activating mammalian skeletal muscle L-channels are capable of undergoing rapid, voltage-dependent transitions during channel activation. The transitions underlying rapid L-channel activation may reflect rapid transitions of the voltage sensor used to trigger the release of calcium from the sarcoplasmic reticulum during excitation-contraction coupling.

Animals↗
PubMed1986

Differential effect of denervation on free-radical scavenging enzymes in slow and fast muscle of rat.

To determine the effect of denervation on the free-radical scavenging systems in relation to the mitochondrial oxidative metabolism in the slow-twitch soleus and fast-twitch extensor digitorum longus (EDL) muscles, the sciatic nerve of the rat was crushed in the midthigh region and the muscle tissue levels of five enzymes were studied 2 and 5 weeks following crush. Recently developed radioimmunoassays were utilized for the selective measurement of cuprozinc (cytosolic) and mangano (mitochondrial) superoxide dismutases. Total tissue content of cuprozinc superoxide dismutase showed a mild decrease after denervation in slow but not in fast muscle. Manganosuperoxide dismutase and fumarase decreased markedly at 2 weeks and returned toward control levels by 5 weeks, the changes appearing to be greater in slow than in fast muscle. At 2 weeks, cytochrome c oxidase decreased significantly in slow, but not in fast muscle. GSH-peroxidase at baseline was 10-fold higher in slow than in fast muscle, markedly decreased at 2 weeks in slow muscle, and returned toward control levels at 5 weeks, whereas the total enzyme activity in fast muscle did not change through 5 weeks. These data represent the first systematic report of free radical scavenging systems in slow and fast muscles in response to denervation. Selective modification of cuprozinc and manganosuperoxide dismutases and differential regulation of GSH-peroxidase was demonstrated in slow and fast muscle.

Animals↗
PubMed1987

Differential antagonism of the initial fast and secondary slow contractile responses of the rat isolated aorta to 5-hydroxytryptamine by mianserin and ketanserin.

1 The rat isolated aorta is contracted by 5-hydroxytryptamine (5-HT) with an initial fast and secondary slow response. The secondary slow responses were greater than the initial fast. The effects of antagonists (prazosin, idazoxan, phentolamine, dihydroergotamine, methysergide, cyproheptadine, mianserin and ketanserin) on these initial fast and secondary slow contractile responses to 5-HT were studied. 2 Prazosin and idazoxan at 10(-7)M had no effect on responses to 5-HT. Thus all concentrations of 5-HT contract the aorta by stimulating receptors distinct from alpha-adrenoreceptors. 3 Phentolamine, dihydroergotamine, methysergide and cyproheptadine had similar inhibitory effects on the initial fast and secondary slow responses to 5-HT. Phentolamine at 10(-6)M caused parallel, whereas dihydroergotamine (10(-9)-10(-8)M), methysergide (10(-9)-10(-8)M) and cyproheptadine (3 X 10(-11)-10(-8)M) caused non-parallel rightward shifts of the concentration-response curves. 4 Mianserin and ketanserin had greater inhibitory effects on the initial fast than secondary slow responses. Mianserin (10(-9)-10(-7)M) caused a non-parallel and parallel rightward shift of the concentration-response curves to the initial fast and secondary slow responses to 5-HT, respectively. Ketanserin (10(-8)-10(-7)M) produced non-parallel rightward shifts of the concentration-response curves. 5 One possible explanation of these results is that the rat aorta has no spare 5-HT2 receptors and that in inhibiting responses to 5-HT: (a) phentolamine is a competitive antagonist, (b) mianserin and ketanserin are slowly dissociating antagonists, and (c) dihydroergotamine, methysergide and cyproheptadine are irreversible antagonists. Furthermore, the competitive and irreversible antagonists have similar effects on initial fast and secondary slow responses to 5-HT, whereas the slow dissociating antagonists (mianserin and ketanserin) have a greater inhibitory effect on the initial fast than secondary slow response.

Animals↗
PubMed1983

Non-competitive antagonism of the alpha-adrenoceptor-mediated fast component of contraction of rat aorta, by doxazosin and prazosin.

alpha-Adrenoceptor antagonists have been compared for their effects on dose-response curves of fast and slow components of contraction of the rat aorta to noradrenaline (NA). All agents caused a competitive antagonism of the slow component of contraction to NA. The order of potency was: prazosin greater than WB4101 = doxazosin greater than tiodazosin greater than phentolamine greater than corynanthine greater than trimazosin greater than rauwolscine. For the fast component, doxazosin, prazosin, tiodazosin and WB4101 caused some depression of the maximum response. Doxazosin (25 nM) and prazosin (25 nM) produced a complete and unsurmountable antagonism of the maximum fast component. Phentolamine, corynanthine, trimazosin and rauwolscine all competitively antagonized the fast component. The degree of antagonism of the fast component by prazosin and its analogues appeared to be directly related to the potency of individual agents for the slow component. WB4101, which was equipotent with doxazosin and more potent than tiodazosin was less effective than either in reducing the fast component. The antagonism of the fast component by prazosin or doxazosin was easily reversed by washing and prevented by phentolamine (2.5 microM). Neither prazosin nor doxazosin in concentrations of up to 2.5 microM has any effect on contractions of the aorta to 5-hydroxytryptamine (5-HT, 0.25-250 microM) or caffeine (20mM). It is concluded that the ability of some alpha-adrenoceptor antagonists to produce a non-competitive antagonism of the fast component of contraction is (a) dependent upon blockade of alpha-adrenoceptors; (b) unrelated to selectivity for alpha 1-adrenoceptors; (c) related to potency and structure. 8 EGTA (3.0 mM) caused a selective suppression of the slow component of contraction to NA. Both doxazosin and prazosin caused a non-competitive antagonism of EGTA-resistant contractions to NA whereas corynanthine showed competitive antagonism. These observations, together with those above imply that prazosin and doxazosin non-competitively antagonize alpha-adrenoceptorinduced release of calcium in the rat aorta, but competitively antagonize alpha-adrenoceptor-induced calcium entry.

Adrenergic alpha-Antagonists↗
PubMed1995

Bidirectional selective breeding for ethanol effects on locomotor activity: characterization of FAST and SLOW mice through selection generation 35.

Increased recognition of the advantages of genetic animal models has led to heightened interest in their use and development. A replicated bidirectional selective breeding project has produced lines of mice that differ in their locomotor responses to 2.0 g/kg ethanol. FAST-1 and FAST-2 mice are highly stimulated by ethanol (EtOH), whereas SLOW-1 and SLOW-2 mice are either not affected or respond with locomotor depression. Current heritability estimates indicate that approximately 6-8% of the response variance in the FAST lines and 2-10% of the response variance in the SLOW lines is of additive genetic origin. Little systematic response to selection has occurred in recent generations, which implies that the limits of selection have been reached. Analysis of saline activity over 35 generations of selection indicates that baseline activities have not changed during the course of selection in three of the lines, whereas baseline activity of FAST-1 mice has increased slightly. In EtOH dose-response studies (0.5-3.0 g/kg), FAST mice had biphasic dose-response curves, whereas the locomotor activity of SLOW mice was either unaffected or depressed by all doses of EtOH. In addition, FAST mice spent more time in motion, traveled farther per movement, traversed greater distances in the center of the test chamber, and ambulated more quickly than SLOW mice when given EtOH. FAST and SLOW mice differed in EtOH clearance rates; however, the differences were slight relative to the large difference in locomotor response. We encourage the use of FAST and SLOW mice to investigate neurophysiological factors underlying sensitivity to the behavioral effects of EtOH, with a view to further testing of the postulated homology between locomotor stimulant effects and addiction potential of drugs of abuse.

Alcohol Drinking↗
PubMed1998

New evidence that AV node slow pathway conduction directly influences fast pathway function.

INTRODUCTION: Shortening of the AV node fast pathway effective refractory period (ERP) following successful slow pathway ablation may be a nonspecific effect of energy application at the AV junction or may be due to elimination of a direct effect of slow pathway conduction on the fast pathway. METHODS AND RESULTS: Twenty-six consecutive patients (20 women and 6 men; mean age 45 +/- 3 years) with typical AV nodal reentrant tachycardia who underwent successful slow pathway ablation (defined as complete elimination of dual AV node physiology) were studied. The fast pathway ERP (at a drive train cycle length of 600 msec) was determined prior to ablation (baseline) and following unsuccessful and successful ablation attempts. Successful slow pathway ablation shortened the fast pathway ERP significantly (317 +/- 9 msec; P < 0.001) compared to baseline (386 +/- 12 msec), whereas unsuccessful ablations had no effect (376 +/- 11 msec). Sinus cycle length, the AH interval, and blood pressure were unchanged following successful ablation. Shortening of the fast pathway ERP did not correlate with the number of energy applications or with two measures of the proximity between the slow and the fast pathway. CONCLUSION: These results support the hypothesis that shortening of the fast pathway ERP following slow pathway ablation is due to elimination of a direct effect of slow pathway conduction on fast pathway function rather than a nonspecific effect of repeated energy delivery at the AV junction.

Adolescent↗
PubMed1997

Sensitivity and reproducibility of fast-FLAIR, FSE, and TGSE sequences for the MRI assessment of brain lesion load in multiple sclerosis: a preliminary study.

Fast fluid-attenuated inversion recovery (fast-FLAIR), fast spin echo (FSE), and turbo-gradient spin echo (TGSE), new pulse sequences for magnetic resonance imaging (MRI), are able to display multiple sclerosis (MS) lesions more conspicuously (fast-FLAIR) and with shorter imaging times (FSE, TGSE) than is conventional spin-echo MRI. In this study, we scanned 7 MS patients, using fast-FLAIR (18 axial brain slices), FSE (27 slices), and TGSE (9 slices) sequences in the same session, to compare the brain MRI lesion loads detected by these different sequences and the intraobserver reproducibility of these measurements. On the subset of slices (n = 9) covered by all three measurements, the mean lesion load was 7.577 mm3 on fast-FLAIR, 5.248 mm3 on FSE, and 3.080 mm3 on TGSE (p = 0.006) sequences. The mean intraobserver coefficients of variation were 2.92% for fast-FLAIR, 2.86% for FSE, and 4.31% for TGSE (not significant). These findings demonstrate that both fast-FLAIR and FSE sequences may be potentially useful for serial MRI studies for monitoring clinical trials, while TGSE might be useful for speeding diagnostic MRI in MS patients. Longitudinal, clinically correlated studies using these new MRI sequences are needed to confirm these preliminary data.

Brain↗
PubMed1990

Effects of tension and stiffness due to reduced pH in mammalian fast- and slow-twitch skinned skeletal muscle fibres.

1. The pH dependence of the Ca2+ sensitivities of isometric tension and stiffness was investigated at 10 and 15 degrees C in skinned single fibres from rat and rabbit fast- and slow-twitch skeletal muscles. Stiffness was determined by recording the tension responses to sinusoidal length changes (3.3 kHz); peak-to-peak amplitude of the length change was monitored by laser diffraction and averaged approximately 1.3 nm (half-sarcomere)-1. We have assumed that stiffness provides a measure of the number of cross-bridge attachments to actin. 2. At maximal Ca2+ activation, stiffness was depressed by 22 +/- 2% (mean +/- S.E.M.) in fast-twitch fibres but was unchanged in slow-twitch fibres when pH was lowered from 7.00 to 6.20. As reported previously, maximum tension was depressed by 20-45% at low pH, with the effect being greater in fast-twitch compared to slow-twitch fibres. 3. In fast-twitch fibres at 10 and 15 degrees C the Ca2+ concentrations for half-maximal activation of tension and stiffness were increased at low pH. In slow-twitch fibres, similar effects were observed at 15 degrees C, but at 10 degrees C there were no changes in the Ca2+ sensitivities of tension and stiffness when pH was lowered. 4. Linear relationships between relative tension and relative stiffness were obtained at all temperatures, with slopes of 1.04 +/- 0.01 at pH 7.00 and 0.76 +/- 0.01 at pH 6.20 in fast- and slow-twitch fibres, indicating that force per cross-bridge attachment is similarly reduced at low pH in both types of fibres. 5. In both fast- and slow-twitch fibres, rigor tension (no added ATP or creatine phosphate; pCa 9.0) was depressed by 35 +/- 7% and stiffness by 12 +/- 4% when pH was reduced from 7.00 to 6.20. Since cross-bridge cycling is inhibited in rigor the effect of low pH to depress rigor tension suggests that pH directly modulates the strength of the bond formed between actin and myosin. 6. The effect of low pH to reduce the apparent number of cross-bridge attachments during maximal Ca2+ activation in fast- but not slow-twitch fibres could account for the greater H(+)-induced depression of maximum force in fast-twitch fibres. In both fibre types, the decrease in the number of cross-bridge attachments at submaximal concentrations of Ca2+ may in part account for the loss in Ca2+ sensitivity of tension at low pH, due perhaps to a reduction in co-operative activation of the thin filament by bound cross-bridges.

Animals↗
PubMed1992

Slow and fast transient potassium currents in cultured rat hippocampal cells.

1. Potassium currents have been recorded from rat hippocampal neurons in dissociated cultures prepared at E17-E19. Currents were studied with the whole-cell version of the patch clamp method. The kinetics and pharmacological properties of two transient outward currents have been characterized. 2. Most of the recordings have been done in cells which had been in culture 10-18 days. Both a fast and a slow transient current could be elicited. A subtraction procedure was used to isolate the fast transient current. The fast transient current decayed monoexponentially with a time constant of about 10 ms. The slow transient current decayed with two time constants in the order of 500 ms and of 3.4 s. The reversal potential of the slow current shifted by 54 mV for a tenfold change in extracellular potassium concentration. 3. Studies on the removal of inactivation for the two currents revealed time constants of 29 and 107 ms for the fast and slow transient current, respectively. 4. The steady-state inactivation properties of the fast transient current were determined by studying the current with a fixed depolarizing command of -10 mV and varying pre-pulse amplitudes from a holding potential of -50 mV. The inactivation curve could be fitted with a Boltzmann equation. Half-maximal inactivation occurred at -81 mV. The steady-state activation properties of the fast transient current were determined by varying the depolarizing voltage commands following a fixed pre-pulse to -110 mV. The threshold for activation was between -70 and -60 mV. Half-maximal activation was reached at -19 mV. 5. The steady-state inactivation properties of the slow transient current were determined by studying the current elicited by varying the hyperpolarizing voltage steps from a holding potential of 0 mV. The inactivation curve could be fitted with a Boltzmann equation. Half-maximal inactivation was obtained at -61 mV. The steady-state activation properties were determined in a manner similar to the fast current. The threshold for activation was between -40 and -30 mV. 6. The slow transient current was not inactivated immediately when the conditioning pre-pulse was stopped. The rate of current decay increased with stimulus frequency. 7. Both transient currents were sensitive to 4-aminopyridine (4-AP). The fast transient current was blocked completely by 5 mM provided a pre-pulse of 1 s to -110 mV was employed. The slow transient current was already depressed by 4-AP applied in the 100 microM range but could never be blocked completely.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed2004

Fast Ca(2+)-dependent inactivation of the store-operated Ca2+ current (ISOC) in liver cells: a role for calmodulin.

Store-operated Ca2+ channels (SOCs) provide a major pathway for Ca2+ entry in non-excitable cells. SOCs in immortalized liver cells are highly selective for Ca2+ over other cations and are similar to well-studied Ca2+ release activated Ca2+ (CRAC) channels in haematopoietic cell lines. In the present work, employing H4IIE liver cells, we investigated fast inactivation of SOC current (ISOC), which occurs at membrane potentials below -60 mV. This inactivation was significantly reduced when BAPTA, a faster Ca2+ buffer, was used instead of EGTA, and was completely abolished if Na+ was used as a charge carrier in the absence of divalent cations in the external medium. These results suggested that fast inactivation of SOCs in H4IIE cells was Ca2+ dependent and was similar to the fast inactivation of CRAC channels. Experiments showing that the fast inactivation of ISOC was not affected by the disruption of actin by latrunculin B indicate that the cytoskeleton is unlikely to be involved. To elucidate the mechanism of Ca2+ dependence, a possible role of calmodulin (CaM) in SOCs' fast inactivation was investigated. The CaM inhibitors Mas-7 and calmidazolium failed to affect ISOC fast inactivation, whereas over-expression of a CaM inhibitor peptide or a mutant CaM lacking functional EF hands significantly altered the inactivation of ISOC. Out of two exponential components normally required to approximate kinetics of ISOC fast inactivation, the faster component was reduced in amplitude by 30%, compared to the control. The results presented suggest that CaM is responsible for at least part of Ca(2+)-dependent fast inactivation of ISOC in liver cells. It is hypothesized that CaM is tethered to the channel itself and therefore protected from chemical inhibitors.

Adenylyl Cyclases↗
PubMed2005

Extensive syncytium formation mediated by the reovirus FAST proteins triggers apoptosis-induced membrane instability.

The fusion-associated small transmembrane (FAST) proteins of the fusogenic reoviruses are the only known examples of membrane fusion proteins encoded by non-enveloped viruses. While the involvement of the FAST proteins in mediating extensive syncytium formation in virus-infected and -transfected cells is well established, the nature of the fusion reaction and the role of cell-cell fusion in the virus replication cycle remain unclear. To address these issues, we analyzed the syncytial phenotype induced by four different FAST proteins: the avian and Nelson Bay reovirus p10, reptilian reovirus p14, and baboon reovirus p15 FAST proteins. Results indicate that FAST protein-mediated cell-cell fusion is a relatively non-leaky process, as demonstrated by the absence of significant [3H]uridine release from cells undergoing fusion and by the resistance of these cells to treatment with hygromycin B, a membrane-impermeable translation inhibitor. However, diminished membrane integrity occurred subsequent to extensive syncytium formation and was associated with DNA fragmentation and chromatin condensation, indicating that extensive cell-cell fusion activates apoptotic signaling cascades. Inhibiting effector caspase activation or ablating the extent of syncytium formation, either by partial deletion of the avian reovirus p10 ecto-domain or by antibody inhibition of p14-mediated cell-cell fusion, all resulted in reduced membrane permeability changes. These observations suggest that the FAST proteins do not possess intrinsic membrane-lytic activity. Rather, extensive FAST protein-induced syncytium formation triggers an apoptotic response that contributes to altered membrane integrity. We propose that the FAST proteins have evolved to serve a dual role in the replication cycle of these fusogenic non-enveloped viruses, with non-leaky cell-cell fusion initially promoting localized cell-cell transmission of the infection followed by enhanced progeny virus release from apoptotic syncytia and systemic dissemination of the infection.

Animals↗
PubMed2006

Dopamine presynaptically depresses fast inhibitory synaptic transmission via D4 receptor-protein kinase A pathway in the rat dorsolateral septal nucleus.

The lateral septal nucleus receives a diffuse dopaminergic input originating from the ventral tegmental area of the brain stem. We examined whether dopamine (DA) modulates synaptic transmission in the slice preparation of the rat dorsolateral septal nucleus (DLSN). Bath application (10-15 min) of DA (30 muM) markedly depressed the amplitude of fast and slow inhibitory postsynaptic potentials (IPSPs) in DLSN neurons, while it produced only a minor depression of the amplitude of excitatory postsynaptic potentials (EPSPs) obtained in the presence of bicuculline. DA (30 muM) depressed the monosynaptic fast IPSP to approximately 50% of control, but did not depress the inward current (I(GABA)) induced by exogenous gamma-aminobutyric acid (GABA). DA decreased the frequency of miniature fast IPSPs (m-fIPSPs) without significantly changing their amplitude. PD 168077, a selective D4 receptor agonist, depressed the fast and slow IPSPs but not the EPSP and decreased the frequency of m-fIPSPs. Both DA and PD 168077 increased the paired-pulse ratio of the monosynaptic fast IPSP. The inhibitory effect of DA on the fast IPSP was significantly attenuated by L-741,742, an antagonist at D4 receptors, but not by SCH 23390 and sulpiride, a D1-like and a D2-like receptor antagonist, respectively. N-ethylmaleimide, a blocker of pertussis toxin (PTX)-sensitive G protein (G(i/o)), attenuated the DA-induced depression of the fast IPSP. N-[2-((p-bromocinnamyl) amino)ethyl]-5-isoquinoline sulfonamide, a protein kinase A (PKA) inhibitor, attenuated the DA-induced depression of the fast IPSP. These results suggest that DA inhibits spontaneous and evoked release of GABA via the D4 receptor-G(i)-protein-PKA system in DLSN neurons.

Animals↗