scholarly journals Membrane response to current pulses in spheroidal aggregates of embryonic heart cells.

1975 ◽  
Vol 65 (2) ◽  
pp. 207-222 ◽  
Author(s):  
R L Dehaan ◽  
H A Fozzard
Keyword(s):  
Surface Membrane ◽  
Current Source ◽  
Aggregate Size ◽  
Input Resistance ◽  
Membrane Resistance ◽  
Systematic Difference ◽  
Membrane Properties ◽  
Voltage Response ◽  
Heart Cells ◽  
Membrane Area

Hearts from chick embryos aged 4,7, or 14 days were dissociated into their component cells, and the cells allowed to reassociate in the form of smooth-surfaced spheroidal aggregates on a gyratory shaker. Records from intracellular electrodes inserted into two widely spaced cells in a spontaneously beating aggregate indicated that the action potentials occurred virtually simultaneously. In aggregates made quiescent with tetrodotoxin, the voltage response to a current pulse injected in one cell could be noted by recording with a second microelectrode at various distance from the current source. The magnitude of the response was found not to vary with distance. It is concluded that the component cells in an aggregate are normally tightly coupled electrically; the cell boundaries do not constitute an appreciable resistive barrier. Such ag-regates behave as virtually isopential systems, with properties similar to those of single spherical cells, as modeled by Eisenberg and Engel (1970. J. Gen. Physiol. 55:736-757). Passive membrane time constant ranged from 11 to 31 ms, with a mean value of 17 ms; this value did not vary with aggregate size. Input resistance (V/I) varied inversely with aggregate size, as predicted, but with much scatter in the measured values. Specific membrane resistance was calculated as either 13,000 or 800 ohm-cm2 depending on whether input resistance was attributed to the total cell surface membrane area or to the outer surface of the sphere alone. No systematic difference in passive electrical properties of aggregates composed of 4-, 7-, and 14-day cells was seen. It is concluded that these aggregates may be suitable for voltage clamp analysis of their excitable membrane properties.

Membrane resistance increases when automaticity develops in explanted rat heart cells

1990 ◽  
Vol 258 (1) ◽  
pp. H145-H152 ◽  
Author(s):  
O. F. Schanne ◽  
M. Lefloch ◽  
B. Fermini ◽  
E. Ruiz-Petrich
Keyword(s):  
Spontaneous Activity ◽  
Action Potentials ◽  
Ventricular Myocytes ◽  
Input Resistance ◽  
Membrane Resistance ◽  
Resting Potential ◽  
Heart Cells ◽  
Membrane Capacity ◽  
Rat Heart Cells ◽  
Specific Membrane

We compared the passive electrical properties of isolated ventricular myocytes (resting potential -65 mV, fast action potentials, and no spontaneous activity) with those of 2- to 7-day-old cultured ventricle cells from neonatal rats (resting potential -50 mV, slow action potentials, and presence of spontaneous activity). In myocytes the specific membrane capacity was 0.99 microF/cm2, and the specific membrane resistance increased from 2.46 k omega.cm2 at -65 mV to 7.30 k omega.cm2 at -30 mV. In clusters, the current-voltage relationships measured under current-clamp conditions showed anomalous rectification and the input resistance decreased from 1.05 to 0.48 M omega when external K+ concentration was increased from 6 to 100 mM. Using the model of a finite disk we determined the specific membrane resistance (12.9 k omega.cm2), the effective membrane capacity (17.8 microF/cm2), and the lumped resistivity of the disk interior (1,964 omega.cm). We conclude that 1) the voltage dependence of the specific membrane resistance cannot completely explain the membrane resistance increase that accompanies the appearance of spontaneous activity; 2) a decrease of the inwardly rectifying conductance (gk1) is mainly responsible for the increase in the specific membrane resistance and depolarization; and 3) approximately 41% of the inward-rectifying channels are electrically silent when spontaneous activity develops in explanted ventricle cells.

Passive properties of the membrane of single freshly isolated smooth muscle cells

1980 ◽  
Vol 239 (5) ◽  
pp. C153-C161 ◽  
Author(s):  
J. J. Singer ◽  
J. V. Walsh
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Input Resistance ◽  
Muscle Cells ◽  
Membrane Resistance ◽  
Resting Potential ◽  
Stable Steady State ◽  
Membrane Area ◽  
Ion Substitution ◽  
Length Constant

Single, smooth muscle cells were isolated from the stomach muscularis of the toad Bufo marinus and studied on the same day as isolation using standard electrophysiological techniques and direct microscopic observation at high magnification. Following penetration a period of hyperpolarization occurred that appeared to be caused by an increase in K+ conductance activated by Ca2+ entering the cell upon penetration. Ion substitution studies showed that the stable steady-state resting potential was dependent on both [Na+]0 and [K+]0. At [Ca2+]0 = 1.8 mM, active responses could be elicited which, at the higher [Ca2+]0 (< 8mM) generally employed, became action potentials with overshoots. Calculations employing the equations for a short cable and the observed change of membrane potential as a single exponential in response to a small hyperpolarizing current step both indicated that the length constant (lambda) was sufficiently greater than the cell length so that the cell behaved as an isopotential surface during subthreshold perturbations. From photomicrographic measurements of each cell studied and the input resistance, values of specific membrane resistance (Rm) were obtained that ranged as high as 152 k omega x cm2 depending on the ionic environment, most notably on [Ca2+]0. The membrane capacity (Cm) referred to the surface area measured with light microscopy was 1.3 +/- 0.3 microF/cm2 (mean +/- SD). When the best estimate of caveolar membrane area was included, Cm referred to total membrane area (caveolar plus noncaveolar) was approximately 0.8 microF/cm2.

scholarly journals Interactions between Membrane Resistance, GABA-A Receptor Properties, Bicarbonate Dynamics and Cl−-Transport Shape Activity-Dependent Changes of Intracellular Cl− Concentration

2019 ◽  
Vol 20 (6) ◽  
pp. 1416 ◽  
Author(s):  
Aniello Lombardi ◽  
Peter Jedlicka ◽  
Heiko Luhmann ◽  
Werner Kilb
Keyword(s):  
Decay Time ◽  
Gabaa Receptors ◽  
Input Resistance ◽  
Membrane Resistance ◽  
Membrane Properties ◽  
Gaba A ◽  
Cl Transport ◽  
Neuronal Membranes ◽  
Wide Range ◽  
Activity Dependent

The effects of ionotropic γ-aminobutyric acid receptor (GABA-A, GABAA) activation depends critically on the Cl−-gradient across neuronal membranes. Previous studies demonstrated that the intracellular Cl−-concentration ([Cl−]i) is not stable but shows a considerable amount of activity-dependent plasticity. To characterize how membrane properties and different molecules that are directly or indirectly involved in GABAergic synaptic transmission affect GABA-induced [Cl−]i changes, we performed compartmental modeling in the NEURON environment. These simulations demonstrate that GABA-induced [Cl−]i changes decrease at higher membrane resistance, revealing a sigmoidal dependency between both parameters. Increase in GABAergic conductivity enhances [Cl−]i with a logarithmic dependency, while increasing the decay time of GABAA receptors leads to a nearly linear enhancement of the [Cl−]i changes. Implementing physiological levels of HCO3−-conductivity to GABAA receptors enhances the [Cl−]i changes over a wide range of [Cl−]i, but this effect depends on the stability of the HCO3− gradient and the intracellular pH. Finally, these simulations show that pure diffusional Cl−-elimination from dendrites is slow and that a high activity of Cl−-transport is required to improve the spatiotemporal restriction of GABA-induced [Cl−]i changes. In summary, these simulations revealed a complex interplay between several key factors that influence GABA-induced [Cl]i changes. The results suggest that some of these factors, including high resting [Cl−]i, high input resistance, slow decay time of GABAA receptors and dynamic HCO3− gradient, are specifically adapted in early postnatal neurons to facilitate limited activity-dependent [Cl−]i decreases.

Electrotonic architecture of cat gamma motoneurons

1994 ◽  
Vol 72 (5) ◽  
pp. 2302-2316 ◽  
Author(s):  
R. E. Burke ◽  
R. E. Fyffe ◽  
A. K. Moschovakis
Keyword(s):  
Steady State ◽  
Attenuation Factor ◽  
Input Resistance ◽  
Membrane Resistance ◽  
Morphological Data ◽  
Membrane Area ◽  
Current Pulses ◽  
Specific Membrane ◽  
Best Fit ◽  
Calculated Average

1. Experimental measures of input resistance, RN, and responses to brief hyperpolarizing current pulses were obtained in identified gamma-motoneurons in pentobarbital-anesthetized cats using conventional sharp micropipettes. The same cells were subsequently injected with horseradish peroxidase and completely reconstructed. In two cells, the electrophysiological and morphological data were of sufficient quality to permit estimation of specific membrane resistance, Rm, using biologically plausible ranges of specific cytoplasmic resistance, Ri, and membrane capacitance, Cm. 2. A combination of steady-state and dynamic computer models were employed to reconcile cell morphology with RN and the trajectories of the voltage decay following brief current pulses delivered to the soma. Simulated transient responses matched the tails of the observed transient when generated with the same current injections used experimentally. With Cm < or = 1.0 microF cm-2, the most satisfactory fits were obtained when the values of Rm assigned to the soma, Rms, were much smaller than the spatially uniform value assigned to the dendrites, Rmd and Ri = 60–70 omega cm. With Cm = 1.0 microF cm-2, Rms ranged from 260 to 427 omega cm2, whereas Rmd was approximately 33 K omega cm2. With Cm = 0.8 microF cm-2, Rms ranged from 235 to 357 omega cm2 and Rmd was between 62 and 68 K omega cm2. When Rm was constrained to be spatially uniform (i.e., Rm = Rms), implausibly high values of Cm (2.5–5.0 microF cm-2; Ri = 70 omega cm) were required to match the observed tail time constant, tau o,peel, but the simulated transients did not otherwise match those obtained experimentally. 3. With best fit values of Rms and Rmd, both gamma-motoneurons were electronically relatively compact (80% of total membrane area within 0.85 length constants from the soma). However, the calculated average steady-state inward attenuation factor (AFin) for voltages generated at any point within the dendrites increased rapidly with distance from the soma, reaching levels of < or = 90 and < or = 45 for the proximal 80% of membrane area for the respective motoneurons in the presence of a somatic shunt (Rms ≪ Rmd). If we assume that the somatic shunt is an artifact of sharp micropipette penetration (i.e., that Rms = Rmd for uninjured cells), then AFin decreased to < or = 20 and < or = 15, respectively, for the proximal 80% of cell membrane.(ABSTRACT TRUNCATED AT 400 WORDS)

Regional characteristics of the membrane response of an identified crayfish nonspiking interneuron to intracellularly injected current

1995 ◽  
Vol 74 (6) ◽  
pp. 2242-2250 ◽  
Author(s):  
M. Takahashi ◽  
A. Takashima ◽  
M. Takahata
Keyword(s):  
Time Constant ◽  
Regional Difference ◽  
Cell Structure ◽  
Input Resistance ◽  
Resting Potential ◽  
Inward Rectification ◽  
Voltage Response ◽  
Membrane Area ◽  
Geometric Conditions ◽  
Transverse Segment

1. We investigated the membrane response of the local directionally selective (LDS) interneuron, a nonspiking cell identified in the terminal abdominal ganglion of crayfish, to intracellularly injected current in different regions within the cell by single-electrode, discrete current-clamp experiments. The site of electrode impalement into the cell was visualized in situ together with the cell structure under a dissecting microscope. 2. The LDS interneuron has dendritic branches on both hemiganglia connected by a thick segment crossing the midline. Irrespective of the site of electrode impalement, the interneuron showed outward rectification upon depolarization from the resting potential level. When hyperpolarizing current was injected, a linear relationship was observed between the voltage response of the interneuron and the amount of injected current. Upon large hyperpolarization, however, the interneuron showed inward rectification. 3. The input resistance of the interneuron measured within the linear range of the membrane response was significantly lower in the transverse segment than in lateral dendrites (0.001 < P < 0.01). The time constant of the transient voltage response to step current injection was also significantly shorter in the transverse segment than in the lateral dendrites (0.001 < P < 0.01). 4. Although the regional difference in the input resistance could be accounted for, at least partly, by different geometric conditions of each dendritic branch into which current was injected, the regional difference in the time constant of the membrane response cannot be accounted for by structural differences because the time constant is independent of the membrane area. It is thus suggested that the passive properties of the interneuron membrane that are related to its response time constant show regional variability within the cell.

Developmental Changes in Electrophysiological Properties and Synaptic Transmission in Rat Intracardiac Ganglion Neurons

2006 ◽  
Vol 95 (6) ◽  
pp. 3543-3552 ◽  
Author(s):  
Katrina Rimmer ◽  
Alexander A. Harper
Keyword(s):  
Synaptic Transmission ◽  
Postnatal Development ◽  
Input Resistance ◽  
Membrane Resistance ◽  
Membrane Properties ◽  
Right Atrial ◽  
Electrophysiological Properties ◽  
Ganglion Neurons ◽  
Somatic Action Potentials ◽  
Parasympathetic Regulation

We charted postnatal changes in the intrinsic electrophysiological properties and synaptic responses of rat intrinsic cardiac ganglion (ICG) neurons. We developed a whole-mount ganglion preparation of the excised right atrial ganglion plexus. Using intracellular recordings and nerve stimulation we tested the hypothesis that substantial transformations in the intrinsic electrical characteristics and synaptic transmission accompany postnatal development. Membrane potential ( Em) did not change but time constant (τ) and cell capacitance increased with postnatal development. Accordingly, input resistance ( Rin) decreased but specific membrane resistance ( Rm) increased postnatally. Comparison of the somatic active membrane properties revealed significant changes in electrical phenotype. All neonatal neurons had somatic action potentials (APs) with small overshoots and small afterhyperpolarizations (AHPs). Adult neurons had somatic APs with large overshoots and large AHP amplitudes. The range of AHP duration was larger in adults than in neonates. The AP characteristics of juvenile neurons resembled those of adults, with the exception of AHP duration, which fell midway between neonate and adult values. Phasic, multiply adapting, and tonic evoked discharge activities were recorded from ICG neurons. Most neurons displayed phasic discharge at each developmental stage. All neurons received excitatory synaptic inputs from the vagus or interganglionic nerve trunk(s), the strength of which did not change significantly with postnatal age. The changes in the electrophysiological properties of the postganglionic neuron suggest that increased complexity of parasympathetic regulation of cardiac function accompanies postnatal development.

Nonuniform passive membrane properties of rat lumbar sympathetic ganglion cells

1987 ◽  
Vol 57 (3) ◽  
pp. 633-644 ◽  
Author(s):  
S. J. Redman ◽  
E. M. McLachlan ◽  
G. D. Hirst
Keyword(s):  
Time Constant ◽  
Sympathetic Neurons ◽  
Potassium Conductance ◽  
Membrane Conductance ◽  
Input Resistance ◽  
Membrane Properties ◽  
Voltage Response ◽  
Bathing Solution ◽  
Passive Membrane Properties ◽  
Passive Membrane

We have studied the passive membrane properties of sympathetic neurons in isolated lumbar paravertebral ganglia of young rats by recording the voltage response to small steps of current passed through an intracellular microelectrode. Substitution of Ba2+ (2.5 mM) for Ca2+ (2.5 mM) in the bathing solution increased the input resistance and the time constant of the voltage response, but the increase in time constant was disproportionately large relative to the increase in input resistance. After consideration of the passive electrical properties and the geometry of the soma and dendrites, it was concluded that the disproportionate change in input resistance and time constant could be explained if barium inactivated a resting potassium conductance that was concentrated in the distal dendrites. In the APPENDIX, the effect of nonuniform membrane conductance on the relationship between input resistance and time constant in models of these neurons is analyzed.

Effects of diltiazem on smooth muscles and neuromuscular junction in the mesenteric artery

1982 ◽  
Vol 242 (3) ◽  
pp. H325-H336 ◽  
Author(s):  
H. Suzuki ◽  
T. Itoh ◽  
H. Kuriyama
Keyword(s):  
Mesenteric Artery ◽  
Channel Blocker ◽  
Surface Membrane ◽  
Smooth Muscles ◽  
Membrane Resistance ◽  
Membrane Properties ◽  
Ca Channel ◽  
Mechanical Responses ◽  
Ca Antagonist ◽  
Excitatory Junction Potentials

Effects of diltiazem on membrane properties, neuromuscular transmissions, and mechanical responses were investigated in intact and skinned muscles of the guinea pig mesenteric artery. Diltiazem (greater than 10(-6) M) depolarized the membrane, increased the membrane resistance, and suppressed the spike evoked by either electrical depolarization or summation of excitatory junction potentials (EJPs). This drug also suppressed the facilitation process of amplitudes of EJPs produced by repetitive perivascular nerve stimulations. These suppressions of EJPs were not caused by a reduced number of active nerves contributing to the generation of EJP but but rather to a reduction in the release of chemical transmitters. Norepinephrine (NE)-induced and K-induced contractions were suppressed by diltiazem noncompetitively, but the contraction evoked in Na-deficient solution was not suppressed, i.e., diltiazem is not a nonselective inhibitor of the Ca influx. In the saponin-treated skinned muscles diltiazem did not suppress the release from or the accumulation into the Ca store site, nor did it suppress activation of the Ca receptor in contractile proteins. These results indicate that diltiazem acts on the surface membrane and nerve terminal as a Ca antagonist or Ca-channel blocker.

Electrical Coupling and Passive Membrane Properties of AII Amacrine Cells

2010 ◽  
Vol 103 (3) ◽  
pp. 1456-1466 ◽  
Author(s):  
Margaret Lin Veruki ◽  
Leif Oltedal ◽  
Espen Hartveit
Keyword(s):  
Amacrine Cell ◽  
Electrical Coupling ◽  
Amacrine Cells ◽  
Input Resistance ◽  
Membrane Resistance ◽  
Membrane Properties ◽  
Total Input ◽  
Junctional Conductance ◽  
Aii Amacrine Cells ◽  
Aii Amacrine

AII amacrine cells in the mammalian retina are connected via electrical synapses to on-cone bipolar cells and to other AII amacrine cells. To understand synaptic integration in these interneurons, we need information about the junctional conductance ( gj), the membrane resistance ( rm), the membrane capacitance ( Cm), and the cytoplasmic resistivity ( Ri). Due to the extensive electrical coupling, it is difficult to obtain estimates of rm, as well as the relative contribution of the junctional and nonjunctional conductances to the total input resistance of an AII amacrine cell. Here we used dual voltage-clamp recording of pairs of electrically coupled AII amacrine cells in an in vitro slice preparation from rat retina and applied meclofenamic acid (MFA) to block the electrical coupling and isolate single AII amacrines electrically. In the control condition, the input resistance ( Rin) was ∼620 MΩ and the apparent rm was ∼760 MΩ. After block of electrical coupling, determined by estimating gj in the dual recordings, Rin and rm were ∼4,400 MΩ, suggesting that the nongap junctional conductance of an AII amacrine cell is ∼16% of the total input conductance. Control experiments with nucleated patches from AII amacrine cells suggested that MFA had no effect on the nongap junctional membrane of these cells. From morphological reconstructions of AII amacrine cells filled with biocytin, we obtained a surface area of ∼900 μm2 which, with a standard value for Cm of 0.01 pF/μm2, corresponds to an average capacitance of ∼9 pF and a specific membrane resistance of ∼41 kΩ cm2. Together with information concerning synaptic connectivity, these data will be important for developing realistic compartmental models of the network of AII amacrine cells.

Subthreshold frequency selectivity in avian auditory thalamus

1994 ◽  
Vol 71 (4) ◽  
pp. 1361-1372 ◽  
Author(s):  
B. Strohmann ◽  
D. W. Schwarz ◽  
E. Puil
Keyword(s):  
Frequency Selectivity ◽  
Membrane Properties ◽  
Resting Potential ◽  
Resonant Peak ◽  
Auditory Signal ◽  
Voltage Response ◽  
Potential Range ◽  
Na Current ◽  
Frequency Responses ◽  
Low Threshold

1. We studied the frequency responses of neurons in the nucleus ovoidalis (OV), the principal thalamic auditory relay nucleus of the chicken, in the subthreshold range of membrane potentials. The frequency response is the impedance amplitude profile evident in the voltage response to a broadband stimulus. The stimulus was a deterministic periodic current input of small amplitude, sweeping through a specified frequency range. We used whole-cell, tight-seal recording techniques in slices to study the voltage responses and membrane properties in current and voltage clamp. 2. Generally, low-frequency resonant humps with peak impedances of approximately 6 Hz characterized the frequency responses of OV neurons. This resonance was the principal determinant for frequency selectivity in the majority of OV neurons expressing only a tonic mode of firing. 3. The 6-Hz resonance was voltage dependent and most distinct where the activation ranges of a hyperpolarization activated inward current (IH) and a persistent Na+ current tend to overlap. The potential range for optimal resonance often included the resting potential. 4. Application of the Na+ current antagonist, tetrodotoxin, blocked the persistent Na+ current and most of the resonant hump at depolarized levels but did not affect the resonant peak along the frequency axis. Thus the persistent Na+ current may serve to amplify the resonance. 5. Extracellular application of Cs+, but not Ba2+, blocked a voltage sag during pulsed hyperpolarization as well as the IH current. Application of Cs+ also eliminated the 6-Hz resonance. An IH seems, therefore, instrumental for the resonance. 6. A minority of neurons that expressed low-threshold Ca2+ spikes and burst firing at hyperpolarized states displayed voltage oscillations at 2-4 Hz, spontaneously or in response to pulsatile stimuli. Application of Ni2+ blocked the oscillations and the low-threshold spikes, presumably produced by a T-type Ca2+ current. The resonance at 6 Hz, however, was only slightly affected by Ni2+. A T-type current, therefore, is critical for the 2- to 4-Hz oscillations. 7. Membrane resonance may dominate the power spectrum of subthreshold potential fluctuations. The resonance demonstrated in vitro may be stabilized by experimental procedures; its frequency may be different and more variable in vivo. Resonances in thalamic neurons may play a role in auditory signal processing in birds.

Sign in / Sign up

Export Citation Format

Share Document