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PubMed2002

In vitro electrical properties for iridium oxide versus titanium nitride stimulating electrodes.

Stimulating electrode materials must be capable of supplying high-density electrical charge to effectively activate neural tissue. Platinum is the most commonly used material for neural stimulation. Two other materials have been considered: iridium oxide and titanium nitride. This study directly compared the electrical characteristics of iridium oxide and titanium nitride by fabricating silicon substrate probes that differed only in the material used to form the electrode. Electrochemical measurements indicated that iridium oxide had lower impedance and a higher charge storage capacity than titanium nitride, suggesting better performance as a stimulating electrode. Direct measurement of the electrode potential in response to a biphasic current pulse confirmed that iridium oxide uses less voltage to transfer the same amount of charge, therefore using less power. The charge injection limit for titanium nitride was 0.87 mC/cm2, contradicting other reports estimating that titanium nitride was capable of injecting 22 mC/cm2. Iridium oxide charge storage was 4 mC/cm2, which is comparable to other published values for iridium oxide. Electrode efficiency will lead to an overall more efficient and effective device.

Coated Materials, Biocompatible↗
PubMed2004

Internodal myelinated segments: delay and RGC time-domain Green function model.

The myelinated axon can be modeled by means of a distributed RGC circuit. The Green function of this model allows for a generic formulation of the internodal segment response to any kind of stimulus, and accounts for the delay of the action potential associated with this segment. The RGC model accuracy is comparable to that of a more complex electromagnetic model, and predicted delay agrees with experimental measurements.

Action Potentials↗
PubMed2004

Silicon chip with capacitors and transistors for interfacing organotypic brain slice of rat hippocampus.

Probing projections between brain areas and their modulation by synaptic potentiation requires dense arrays of contacts for noninvasive electrical stimulation and recording. Semiconductor technology is able to provide planar arrays with high spatial resolution to be used with planar neuronal structures such as organotypic brain slices. To address basic methodical issues we developed a silicon chip with simple arrays of insulated capacitors and field-effect transistors for stimulation of neuronal activity and recording of evoked field potentials. Brain slices from rat hippocampus were cultured on that substrate. We achieved local stimulation of the CA3 region by applying defined voltage pulses to the chip capacitors. Recording of resulting local field potentials in the CA1 region was accomplished with transistors. The relationship between stimulation and recording was rationalized by a sheet conductor model. By combining a row of capacitors with a row of transistors we determined a simple stimulus-response matrix from CA3 to CA1. Possible contributions of inhomogeneities of synaptic projection, of tissue structure and of neuroelectronic interfacing were considered. The study provides the basis for a development of semiconductor chips with high spatial resolution that are required for long-term studies of topographic mapping.

Animals↗
PubMed1995

Sweat secretion, stratum corneum hydration, small nerve function and pruritus in patients with advanced chronic renal failure.

Sweat secretion, stratum corneum hydration and small nerve fibre function were measured in 40 patients with advanced chronic renal failure (CRF), using pilocarpine iontophoresis, electrical capacitance and a thermal sensory analyser which measures the thresholds of warm and heat pain sensation. Correlations were sought between these parameters, and the presence and severity of pruritus and skin xerosis were compared with 45 healthy control subjects. The mean sweat secretion and stratum corneum hydration of CRF patients were significantly lower than in controls. Thirteen patients had pathological thresholds to warm sensation on the foot, and eight on the hand. None had pathological thresholds to heat-pain. The presence of pruritus did not correlate with any of the following: xerosis, stratum corneum hydration, sweat secretion or the results of thermal testing.

Aged↗
PubMed2006

A local GABAergic system within rat trigeminal ganglion cells.

We investigated the GABAergic system within the Sprague-Dawley rat (2-3-weeks old) trigeminal ganglion (TG). Reverse transcription-polymerase chain reaction (RT-PCR) analysis revealed expression of glutamate decarboxylase (GAD) 65 and GAD67 mRNAs and mRNAs encoding GABA(A) receptor subunits alpha1-6, beta1-3, gamma1-3, and delta. In situ hybridization revealed that GAD65 and GAD67 mRNAs were expressed in neuronal cell bodies but not satellite cells. Immunohistochemical analysis showed that only GAD65 was expressed in all neuronal cell bodies, and approximately 70% of all neurons exhibited GABA immunoreactivity. Satellite cells were strongly immunopositive for GABA. GABA(A) receptor alpha1, alpha5, beta2/3 and gamma1/2/3 subunit immunoreactivities were observed in the majority of neurons, but no immunoreactivity for alpha2 was observed. Two types of cells were identified in TG based on cell size and morphology, type A and B. The percentage of cells expressing alpha3, alpha4, alpha6, and delta subunits appeared to be dependent on cell size, as delta and alpha6 expression were only observed in small (B-type) neurons. In whole-cell patch clamp experiments, GABA application induced inward Cl- currents in all neurons examined. The EC50 for GABA varied from 5.3 to 240 microm, and the Hill Coefficient (nH) varied between 0.98 and 2.6 at -60 mV. We found that GABA was released from TG cells by increasing extracellular K+ concentration to 100 mm. We speculate that GABA acts as a nonsynaptically released diffusible neurotransmitter, which may modulate somatic inhibition of neurons within the TG.

Animals↗
PubMed1995

Measurement of skin hydration in normal dogs and in dogs with atopy or a scaling dermatosis.

The role of the stratum corneum both as a barrier to water loss from the body and as a biological microenvironment is well recognised, although most discussion of these topics is expressed in qualitative terms. This paper describes the use of techniques for the measurement of some aspects of the skin microclimate, and their application to canine skin. The techniques used were the assessment of skin moisture, hygroscopicity and water-holding capacity by measurement of skin electrical capacitance. Meaningful deductions regarding the water dynamics of certain skin sites can be drawn, and it was shown that significant differences in hydration exist between different skin sites. The techniques were also used to show that scaly skin is 'drier' than normal skin, and that the water dynamics of the non-lesional skin of atopic dogs does not differ from that of normal dogs.

Analysis of Variance↗
PubMed1992

Cyclic GMP-activated channels of salamander retinal rods: spatial distribution and variation of responsiveness.

1. Patch-clamp methods were used to investigate the areal density and spatial location of cyclic GMP-activated channels in the surface membrane of salamander rod outer segments. 2. The density of active channels (i.e. channels able to respond to cyclic GMP) in patches excised from outer segments was determined from the number of active channels, N, and the membrane area, A. N was estimated from the current induced by a saturating concentration of cyclic GMP, while A was estimated from the electrical capacitance of the patch. 3. In patches excised from forty-one isolated outer segments prepared in the light the active channel density varied over a remarkable range: 0.34-629 microns-2, with a mean of 166 microns-2. Density was not correlated with patch area in this or any of the conditions studied. 4. The spatial distribution of open channels on the outer segment of a transducing rod was measured by recording the local dark current at various positions with a loose-patch electrode. The apparent density of open channels varied by only about +/- 50% around the circumference of the outer segment and up and down its length. This indicates that the wide range of densities in excised patches did not result from sampling a non-uniform spatial distribution of channels. 5. Patches excised from sixteen dark-adapted whole cells with healthy appearances and saturating light responses of normal size had active channel densities of 1.1-200 microns-2, with a mean of 60 microns-2. Patches from twenty light-adapted whole cells had similar densities. Many densities from the whole cells were much lower than expected. This, and the wide variation in densities, suggests that obtaining a patch often lowered the density of active channels. The number of channels in a patch was quite stable from 1 s to 30 min after excision, ruling out progressive denaturation or adsorption of channels to the glass as a cause for this effect. 6. The mean active channel density in patches excised from whole cells was lower with calcium present in the external solution than with calcium absent (80 vs. 152 microns-2, n = 36 and 30 respectively). 7. We conclude that copies of the channel protein were present at a density of at least 650 microns-2 in the surface membrane of the outer segment and that the distribution of channels was fairly uniform on a 1 micron scale.(ABSTRACT TRUNCATED AT 400 WORDS)

Adaptation, Ocular↗
PubMed2003

Cl- flux through a non-selective, stretch-sensitive conductance influences the outer hair cell motor of the guinea-pig.

Outer hair cells underlie high frequency cochlear amplification in mammals. Fast somatic motility can be driven by voltage-dependent conformational changes in the motor protein, prestin, which resides exclusively within lateral plasma membrane of the cell. Yet, how a voltage-driven motor could contribute to high frequency amplification, despite the low-pass membrane filter of the cell, remains an enigma. The recent identification of prestin's Cl- sensitivity revealed an alternative mechanism in which intracellular Cl- fluctuations near prestin could influence the motor. We report the existence of a stretch-sensitive conductance within the lateral membrane that passes anions and cations and is gated at acoustic rates. The resultant intracellular Cl- oscillations near prestin may drive motor protein transitions, as evidenced by pronounced shifts in prestin's state-probability function along the voltage axis. The sensitivity of prestin's state probability to intracellular Cl- levels betokens a more complicated role for Cl- than a simple extrinsic voltage sensor. Instead, we suggest an allosteric modulation of prestin by Cl- and other anions. Finally, we hypothesize that prestin sensitivity to anion flux through the mechanically activated lateral membrane can provide a driving force that circumvents the membrane's low-pass filter, thus permitting amplification at high acoustic frequencies.

Animals↗
PubMed2003

Regional distribution of hyperpolarization-activated current (If) and hyperpolarization-activated cyclic nucleotide-gated channel mRNA expression in ventricular cells from control and hypertrophied rat hearts.

Hyperpolarization-activated inward current (If) and changes in the messenger RNA (mRNA) expression levels of hyperpolarization-activated cyclic nucleotide-gated channel (HCN)2 and HCN4 encoding If channels of the rat heart were studied in control and hypertrophied myocytes isolated from three ventricular regions: the septum (S), the left ventricular free wall (LV) and the right ventricular free wall (RV). Electrophysiological experiments were conducted by ruptured and perforated-patch clamp techniques and quantification of mRNA levels was carried out by quantitative reverse transcriptase polymerase chain reaction. The occurrence, density and maximal specific conductance of If were found to be significantly higher in hypertrophied ventricular myocytes isolated from S and LV than in those isolated from RV or sham-operated rats. Half-maximal activation potential, the slope of the activation curve and the threshold for activation were similar in ventricular myocytes from sham and aortic stenosed rats in the three regions studied. Isoproterenol 1 micromol l-1 increased current size by shifting current activation to more positive potentials in both sham and hypertrophied myocytes. When we studied the mRNA levels of If channel isoforms present in the ventricle, we found a significant increase of HCN2 and HCN4 mRNA levels in hypertrophied myocytes from S and LV but not in RV. We conclude that the occurrence, density and conductance of If is higher in hypertrophied than in control ventricular myocytes, S being the region where all these changes were most evident. These findings are associated with a higher expression of HCN2 and HCN4 mRNA levels in the two regions that developed hypertrophy.

Action Potentials↗
PubMed2006

Unitary IPSPs enhance hilar mossy cell gain in the rat hippocampus.

Mechanisms that control neuronal gain allow for adaptive rescaling to synaptic inputs of varying strengths or frequencies. Here, we show that unitary IPSPs (uIPSPs) modulate gain and unitary EPSP (uEPSP)-action potential coupling in mossy cells (MCs) from rat hippocampal slices. Mossy fibre-evoked uEPSCs were large, facilitated and were suppressed by the group II metabotropic glutamate agonist LY354740. Conversely, uIPSCs were smaller, depressed and were not affected by LY354740, but exerted strong inhibitory control over uEPSP-action potential coupling. The IPSC reversal potential was determined by gramicidin perforated patch recordings to be -65.3 +/- 5.0 mV, lying between the resting membrane potential (-75.3 +/- 1.1 mV) and the action potential threshold (-56.5 +/- 2.4 mV). When applied at theta frequency (10 Hz), uIPSPs increased the offset of the MC input-output response to depolarizing current injection, but also increased gain, maximal firing rate and the slope of the depolarization preceding action potentials. These effects were unchanged by the Ca2+ and HCN channel blockers mibefradil and ZD7288, respectively. The height and maximal slope of MC action potentials during tonic depolarization were also increased by uIPSPs, and the decay of uIPSP conductances injected by dynamic clamp at subthreshold membrane potentials was prolonged by TTX. Application of the muscarinic agonist pilocarpine mimicked the effect of IPSPs on MC maximal firing rate, and action potential height and slope, and this was reversed by the GABA(A) antagonist gabazine. Thus, uIPSPs can increase neuronal gain under hyperexcitable conditions, and this effect is probably due to the de-inactivation of a TTX-sensitive voltage-dependent Na+ conductance.

2-Amino-5-phosphonovalerate↗
PubMed2004

Transmembrane segments of syntaxin line the fusion pore of Ca2+-triggered exocytosis.

The fusion pore of regulated exocytosis is a channel that connects and spans the vesicle and plasma membranes. The molecular composition of this important intermediate structure of exocytosis is unknown. Here, we found that mutations of some residues within the transmembrane segment of syntaxin (Syx), a plasma membrane protein essential for exocytosis, altered neurotransmitter flux through fusion pores and altered pore conductance. The residues that influenced fusion-pore flux lay along one face of an alpha-helical model. Thus, the fusion pore is formed at least in part by a circular arrangement of 5 to 8 Syx transmembrane segments in the plasma membrane.

Animals↗
PubMed1959

Low-level x-ray damage to amphibian erythrocytes.

In vitro x-irradiation of frog and Amphiuma erythrocytes caused cytophysiological damage to part of the cell population. There was a significant decrease in the percentage of normal cells and some hemolysis. Changes were also observed in the electrical capacitance and potassium-42 uptake of irradiated erythrocytes.

Amphibians↗
PubMed2000

Role of the cytoplasmic tail of ecotropic moloney murine leukemia virus Env protein in fusion pore formation.

Fusion between cells expressing envelope protein (Env) of Moloney murine leukemia virus and target cells were studied by use of video fluorescence microscopy and electrical capacitance measurements. When the full-length 632-amino-acid residue Env was expressed, fusion did not occur at all for 3T3 cells as target and only somewhat for XC6 cells. Expression of Env 616*-a construct of Env with the last 16 amino acid residues (617 to 632; the R peptide) deleted from its C terminus to match the proteolytically cleaved Env produced during viral budding-resulted in high levels of fusion. Env 601*, lacking the entire cytoplasmic tail (CT) (identified by hydrophobicity), also led to fusion. Truncation of an additional six residues (Env 595*) abolished fusion. The kinetics of forming fusion pores did not depend on whether cells were first prebound at 4 degrees C and the time until fusion measured after the temperature was raised to 37 degrees C or whether cells were first brought into contact at 37 degrees C and the time until fusion immediately measured. This similarity in kinetics indicates that binding is accomplished quickly compared to subsequent steps in fusion. The fusion pores formed by Env 601* and Env 616* had the same initial size and enlarged in similar manners. Thus, once the R peptide is removed, the CT is not needed for fusion and does not affect formed pores. However, residues 595 to 601 are required for fusion. It is suggested here that the ectodomain and membrane-spanning domain of Env are directly responsible for fusion and that the R peptide affects their configurations at some point during the fusion process, thereby indirectly controlling fusion.

3T3 Cells↗
PubMed1980

Membrane electricity as a convertible energy currency for the cell.

The role of transmembrane electric potential difference (delta psi) in mitochondria, chloroplasts, and bacteria has been considered. Since the electric capacitance of membranes is much lower than the pH buffer capacitance of water phases, delta psi proves to be the primary form of energy produced by generators of electrochemical H+ potential difference (delta mu-H). There are 11 distinct types of delta mu-H-generating systems in coupling membranes, involved in respiratory and light-dependent electron and proton transfer, as well as in ATP and PP1 hydrolysis and synthesis. Bacteriorhodopsin is the simplest delta mu-H generator. However, even in this case, the molecular mechanism of delta psi production remains obscure. Many types of work can be supported by delta mu-H with no ATP involved so that delta mu-H proves to be not only a transient intermediate of oxidative and photosynthetic phosphorylation but also a convertible energy currency for the cell. Among the delta mu-H-supported activities, mechanical work was recently demonstrated. It can be exemplified by the motility systems of (i) flagellar bacteria and (ii) blud--green algae. As was found in multicellular cyanobacteria, delta mu-H can be used for a power transmission over distances as long as 1 mm. It seems to be probable that in large cells of eukaryotes (e.g., in muscle fibers) giant mitochondria may serve as power-transmitting structures. Na+--K+ gradients can be used to stabilize delta mu-H in bacteria. It is suggested that the primary function of unequal distribution of these cations between the microbial cell and the medium is delta mu-H buffering.

Adenosine Triphosphate↗
PubMed2003

A voltage-gated K(+) current in renal inner medullary collecting duct cells.

We studied the K(+)-selective conductances in primary cultures of rat renal inner medullary collecting duct (IMCD) using perforated-patch and conventional whole cell techniques. Depolarizations above -20 mV induced a time-dependent outward K(+) current (I(vto)) similar to a delayed rectifier. I(vto) showed a half-maximal activation around 5.6 mV with a slope factor of 6.8 mV. Its K(+)/Na(+) selectivity ratio was 11.7. It was inhibited by tetraethylammonium, quinidine, 4-aminopyridine, and Ba(2+) and was not Ca(2+) dependent. The delayed rectifying characteristics of I(vto) prompted us to screen the expression of Kv1 and Kv3 families by RT-PCR. Analysis of RNA isolated from cell cultures revealed the presence of three Kv alpha-subunits (Kv1.1, Kv1.3, and Kv1.6). Western blot analysis with Kv alpha-subunit antibodies for Kv1.1 and Kv1.3 showed labeling of approximately 70-kDa proteins from inner medulla plasmatic and microsome membranes. Immunocytochemical analysis of cell culture and kidney inner medulla showed that Kv1.3 is colocalized with the Na(+)-K(+)-ATPase at the basolateral membrane, although it is also in the cytoplasm. This is the first evidence of recording, protein expression, and localization of a voltage-gated Kv1 in the kidney IMCD cells.

Animals↗
PubMed2002

Ca2+-activated Cl- current in cultured myenteric neurons from murine proximal colon.

Whole cell patch-clamp recordings were made from cultured myenteric neurons taken from murine proximal colon. The micropipette contained Cs(+) to remove K(+) currents. Depolarization elicited a slowly activating time-dependent outward current (I(tdo)), whereas repolarization was followed by a slowly deactivating tail current (I(tail)). I(tdo) and I(tail) were present in approximately 70% of neurons. We identified these currents as Cl(-) currents (I(Cl)), because changing the transmembrane Cl(-) gradient altered the measured reversal potential (E(rev)) of both I(tdo) and I(tail) with that for I(tail) shifted close to the calculated Cl(-) equilibrium potential (E(Cl)). I(Cl) are Ca(2+)-activated Cl(-) current [I(Cl(Ca))] because they were Ca(2+) dependent. E(Cl), which was measured from the E(rev) of I(Cl(Ca)) using a gramicidin perforated patch, was -33 mV. This value is more positive than the resting membrane potential (-56.3 +/- 2.7 mV), suggesting myenteric neurons accumulate intracellular Cl(-). omega-Conotoxin GIVA [0.3 microM; N-type Ca(2+) channel blocker] and niflumic acid [10 microM; known I(Cl(Ca)) blocker], decreased the I(Cl(Ca)). In conclusion, these neurons have I(Cl(Ca)) that are activated by Ca(2+) entry through N-type Ca(2+) channels. These currents likely regulate postspike frequency adaptation.

Animals↗
PubMed2004

Inhibition of chloride secretion in human bronchial epithelial cells by cigarette smoke extract.

Chronic bronchitis, a disease mainly of cigarette smokers, shares many clinical features with cystic fibrosis, a disease of altered ion transport, suggesting that the negative effects of cigarette smoke on mucociliary clearance may be mediated through alterations in ion transport. We tested the hypothesis that cigarette smoke extract would inhibit chloride secretion in human bronchial epithelial cells. In agreement with studies in canine trachea, cigarette smoke extract inhibited net chloride secretion without affecting sodium transport. We performed microelectrode impalements and impedance analysis studies to investigate the physiological mechanisms of this inhibition. These data demonstrated that cigarette smoke extract caused an acute increase in membrane resistances in conjunction with apical membrane hyperpolarization, an effect consistent with inhibition of an apical membrane anion conductance. After this acute phase, both membrane resistances decreased while membrane potentials continued to hyperpolarize, indicating that cigarette smoke extract also inhibited the basolateral entry of chloride into the cell. Furthermore, cigarette smoke extract caused an increase in mucin secretion. Therefore, the ion transport phenotype of human bronchial epithelial cells exposed to cigarette smoke extract is similar to that of cystic fibrosis epithelia in which there is sodium absorption out of proportion to chloride secretion in the setting of increased mucus secretion.

Bronchi↗