scholarly journals Ionic properties of the acetylcholine receptor in cultured rat myotubes.

1975 ◽  
Vol 65 (6) ◽  
pp. 751-767 ◽  
Author(s):  
A K Ritchie ◽  
D M Fambrough
Keyword(s):  
Equivalent Circuit ◽  
Reversal Potential ◽  
Electrical Circuit ◽  
Frog Muscle ◽  
Constant Field ◽  
Adult Rat ◽  
Wide Range ◽  
Goldman Equation ◽  
Alpha Bungarotoxin ◽  
External Ph

The acetylcholine reversal potential (Er) of cultured rat myotubes is -3mV. When activated, the receptor is permeable to K+ and Na+, but not to Cl- ions. Measurement of Er in Tris+-substituted, Na-free medium also indicated a permeability to Tris+ ions. Unlike adult frog muscle the magnitude of Er was insensitive to change in external Ca++ (up to 30 mM) or to changes in external pH (between 6.4 and 8.9). The equivalent circuit equation describing the electrical circuit composed of two parallel ionic batteries (EK and ENa) and their respective conductances (gK and gNa), which has been generally useful in describing the Er of adult rat and frog muscle, could also be applied to rat myotubes when Er was measured over a wide range of external Na+ concentrations. The equivalent circuit equation could not be applied to myotubes bathed in media of different external K+ concentrations. In this case, the Er was more closely described by the Goldman constant field equation. Under certain circumstances, it is known that the receptor in adult rat and frog muscle can be induced to reversibly shift from behavior described by the equivalent circuit equation to that described by the Goldman equation. Attempts to similarly manipulate the responses of cultured rat myotubes were unsussessful. These trials included a reduction in temperature (15 degress C), partial alpha-bungarotoxin blodkade, and activation of responses with the cholinergic agonist, decamethonium.

Evaluation and Validation of Equivalent Circuit Photovoltaic Solar Cell Performance Models

2011 ◽  
Vol 133 (2) ◽  
Author(s):  
Matthew T. Boyd ◽  
Sanford A. Klein ◽  
Douglas T. Reindl ◽  
Brian P. Dougherty
Keyword(s):  
Amorphous Silicon ◽  
Equivalent Circuit ◽  
Model Performance ◽  
Band Gap Energy ◽  
Open Circuit ◽  
Electrical Circuit ◽  
Performance Model ◽  
Current Output ◽  
Solar Cell Performance ◽  
Wide Range

The “five-parameter model” is a performance model for photovoltaic solar cells that predicts the voltage and current output by representing the cells as an equivalent electrical circuit with radiation and temperature-dependent components. An important feature of the five-parameter model is that its parameters can be determined using data commonly provided by module manufacturers on their published datasheets. This paper documents the predictive capability of the five-parameter model and proposes modifications to improve its performance using approximately 30 days of field-measured meteorological and module data from a wide range of cell technologies, including monocrystalline, polycrystalline, amorphous silicon, and copper indium diselenide (CIS). The standard five-parameter model is capable of predicting the performance of monocrystalline and polycrystalline silicon modules within approximately 6% RMS but is slightly less accurate for a thin-film CIS and an amorphous silicon array. Errors for the amorphous technology are reduced to approximately 5% RMS by using input data obtained after the module underwent an initial degradation in output due to aging. The robustness and possible improvements to the five-parameter model were also evaluated. A sensitivity analysis of the five-parameter model shows that all model inputs that are difficult to determine and not provided by manufacturer datasheets such as the glazing material properties, the semiconductor band gap energy, and the ground reflectance may be represented by approximate values independent of the PV technology. Modifications to the five-parameter model tested during this research did not appreciably improve the overall model performance. Additional dependence introduced by a seven-parameter model had a less than 1% RMS effect on maximum power predictions for the amorphous technology and increased the modeling errors for this array 4% RMS at open-circuit conditions. Adding a current sink to the equivalent circuit to better model recombination currents had little effect on the model behavior.

Possible Effects of Depolarizing GABAA Conductance on the Neuronal Input–Output Relationship: A Modeling Study

2005 ◽  
Vol 93 (6) ◽  
pp. 3504-3523 ◽  
Author(s):  
Kenji Morita ◽  
Kunichika Tsumoto ◽  
Kazuyuki Aihara
Keyword(s):  
Firing Rate ◽  
Cortical Neurons ◽  
Reversal Potential ◽  
Pyramidal Cells ◽  
Resting Potential ◽  
Input Output ◽  
Wide Range ◽  
The Relationship

Recent in vitro experiments revealed that the GABAA reversal potential is about 10 mV higher than the resting potential in mature mammalian neocortical pyramidal cells; thus GABAergic inputs could have facilitatory, rather than inhibitory, effects on action potential generation under certain conditions. However, how the relationship between excitatory input conductances and the output firing rate is modulated by such depolarizing GABAergic inputs under in vivo circumstances has not yet been understood. We examine herewith the input–output relationship in a simple conductance-based model of cortical neurons with the depolarized GABAA reversal potential, and show that a tonic depolarizing GABAergic conductance up to a certain amount does not change the relationship between a tonic glutamatergic driving conductance and the output firing rate, whereas a higher GABAergic conductance prevents spike generation. When the tonic glutamatergic and GABAergic conductances are replaced by in vivo–like highly fluctuating inputs, on the other hand, the effect of depolarizing GABAergic inputs on the input–output relationship critically depends on the degree of coincidence between glutamatergic input events and GABAergic ones. Although a wide range of depolarizing GABAergic inputs hardly changes the firing rate of a neuron driven by noncoincident glutamatergic inputs, a certain range of these inputs considerably decreases the firing rate if a large number of driving glutamatergic inputs are coincident with them. These results raise the possibility that the depolarized GABAA reversal potential is not a paradoxical mystery, but is instead a sophisticated device for discriminative firing rate modulation.

scholarly journals Effect of acetylcholine on postjunctional membrane permeability in eel electroplaque.

1977 ◽  
Vol 70 (1) ◽  
pp. 23-36 ◽  
Author(s):  
N L Lassignal ◽  
A R Martin
Keyword(s):  
Field Equation ◽  
Membrane Potential ◽  
Membrane Permeability ◽  
Ionic Composition ◽  
Reversal Potential ◽  
Resting Potential ◽  
Constant Field ◽  
Free Solution ◽  
Positive Direction ◽  
External K

Acetylcholine (ACh) was applied iontophoretically to the innervated face of isolated eel electroplaques while the membrane potential was being recorded intracellularly. At the resting potential (about -85 mV) application of the drug produced depolarizations (ACh potentials) of 20 mV or more which became smaller when the membrane was depolarized and reversed in polarity at about zero membrane potential. The reversal potential shifted in the negative direction when external Na+ was partially replaced by glucosamine. Increasing external K+ caused a shift of reversal potential in the positive direction. It was concluded that ACh increased the permeability of the postjunctional membrane to both ions. Replacement of Cl- by propionate had no effect on the reversal potential. In Na+-free solution containing glucosamine the reversal potential was positive to the resting potential, suggesting that ACh increased the permeability to glucosamine. Addition of Ca++ resulted in a still more positive reversal potential, indicating an increased permeability to Ca++ as well. Analysis of the results indicated that the increases in permeability of the postjunctional membrane to K+, Na+, Ca++, and glucosamine were in the ratios of approximately 1.0:0.9:0.7:0.2, respectively. With these permeability ratios, all of the observed shifts in reversal potential with changes in external ionic composition were predicted accurately by the constant field equation.

scholarly journals Stretch-activated whole cell currents in adult rat cardiac myocytes

2000 ◽  
Vol 278 (2) ◽  
pp. H548-H557 ◽  
Author(s):  
Tao Zeng ◽  
Glenna C. L. Bett ◽  
Frederick Sachs
Keyword(s):  
Single Channel ◽  
Ventricular Myocytes ◽  
Reversal Potential ◽  
Cell Voltage ◽  
Cellular Level ◽  
Whole Cell ◽  
Adult Rat ◽  
Longitudinal Stretch ◽  
Single Channel Currents ◽  
Channel Currents

Mechanoelectric transduction can initiate cardiac arrhythmias. To examine the origins of this effect at the cellular level, we made whole cell voltage-clamp recordings from acutely isolated rat ventricular myocytes under controlled strain. Longitudinal stretch elicited noninactivating inward cationic currents that increased the action potential duration. These stretch-activated currents could be blocked by 100 μM Gd3+ but not by octanol. The current-voltage relationship was nearly linear, with a reversal potential of approximately −6 mV in normal Tyrode solution. Current density varied with sarcomere length (SL) according to I (pA/pF) = 8.3 − 5.0SL (μm). Repeated attempts to record single channel currents from stretch-activated ion channels failed, in accord with the absence of such data from the literature. The inability to record single channel currents may be a result of channels being located on internal membranes such as the T tubules or, possibly, inactivation of the channels by the mechanics of patch formation.

scholarly journals Ih Without Kir in Adult Rat Retinal Ganglion Cells

2007 ◽  
Vol 97 (5) ◽  
pp. 3790-3799 ◽  
Author(s):  
Sherwin C. Lee ◽  
Andrew T. Ishida
Keyword(s):  
Ganglion Cell ◽  
Retinal Ganglion Cells ◽  
Ganglion Cells ◽  
Reversal Potential ◽  
Inward Rectification ◽  
Retinal Ganglion ◽  
Membrane Hyperpolarization ◽  
Adult Rat ◽  
Inwardly Rectifying ◽  
Cell Somata

Antisera directed against hyperpolarization-activated mixed-cation (“ Ih”) and K+ (“Kir”) channels bind to some somata in the ganglion cell layer of rat and rabbit retina. Additionally, the termination of hyperpolarizing current injections can trigger spikes in some cat retinal ganglion cells, suggesting a rebound depolarization arising from activation of Ih. However, patch-clamp studies showed that rat ganglion cells lack inward rectification or present an inwardly rectifying K+ current. We therefore tested whether hyperpolarization activates Ih in dissociated, adult rat retinal ganglion cell somata. We report here that, although we found no inward rectification in some cells, and a Kir-like current in a few cells, hyperpolarization activated Ih in roughly 75% of the cells we recorded from in voltage clamp. We show that this current is blocked by Cs+ or ZD7288 and only slightly reduced by Ba2+, that the current amplitude and reversal potential are sensitive to extracellular Na+ and K+, and that we found no evidence of Kir in cells presenting Ih. In current clamp, injecting hyperpolarizing current induced a slowly relaxing membrane hyperpolarization that rebounded to a few action potentials when the hyperpolarizing current was stopped; both the membrane potential relaxation and rebound spikes were blocked by ZD7288. These results provide the first measurement of Ih in mammalian retinal ganglion cells and indicate that the ion channels of rat retinal ganglion cells may vary in ways not expected from previous voltage and current recordings.

scholarly journals Rotational diffusion of acetylcholine receptors on cultured rat myotubes.

1990 ◽  
Vol 110 (6) ◽  
pp. 2049-2059 ◽  
Author(s):  
M Velez ◽  
K F Barald ◽  
D Axelrod
Keyword(s):  
Acetylcholine Receptors ◽  
Fluorescence Recovery After Photobleaching ◽  
Rotational Diffusion ◽  
Cytochalasin D ◽  
Fluorescence Probes ◽  
Rotational Mobility ◽  
Polarized Fluorescence ◽  
Cytoplasmic Actin ◽  
Wide Range ◽  
Alpha Bungarotoxin

The rotational mobility of acetylcholine receptors (AChR) in the plasma membrane of living rat myotubes in culture is measured in this study by polarized fluorescence recovery after photobleaching (PFRAP). These AChR are known to exist in two distinct classes, evident by labeling with rhodamine alpha-bungarotoxin; clustered AChR that are aggregated in a pattern of highly concentrated speckles and streaks, with each cluster occupying an area of approximately 1,000 microns 2; and nonclustered AChR that appear as diffuse labeling. PFRAP results reported here show that: (a) most clustered AChR (approximately 86%) are rotationally immobile within a time scale of at least several seconds; and (b) most nonclustered AChR (approximately 76%) are rotationally mobile with characteristic times ranging from less than 50 ms to 0.1 s. External cross-linking with the tetravalent lectin concanavalin A immobilizes many nonclustered AChR. PFRAP experiments in the presence of carbachol or cytochalasin D show that the restraints to rotational motion in clusters are remarkably immune to treatments that disperse clusters or disrupt cytoplasmic actin. The experiments also demonstrate the feasibility of using PFRAP to measure rotational diffusion on selected microscopic areas of living nondeoxygenated cells labeled with standard fluorescence probes over a very wide range of time scales, and they also indicate what technical improvements would make PFRAP even more practicable.

scholarly journals Permeability of the sodium channel in Myxicola to organic cations.

1976 ◽  
Vol 68 (5) ◽  
pp. 551-562 ◽  
Author(s):  
L Binstock
Keyword(s):  
Sodium Channels ◽  
Organic Cation ◽  
Reversal Potential ◽  
Node Of Ranvier ◽  
Ionic Currents ◽  
Giant Axon ◽  
Organic Cations ◽  
Relative Permeabilities ◽  
Potential Control ◽  
Goldman Equation

The relative permeability of sodium channels to organic cations was determined in the Myxicola giant axon. Ionic currents under potential control were measured in seawater and in sodium-free solutions containing the organic cation. The measured reversal potential and the Goldman equation were used to obtain the relative permeabilities. The permeability sequence was found to be: sodium greater than hydroxylamine greater than hydrazine greater than ammonium greater than guanidine greater than formamidine greater than aminoguanidine greater than methylamine. Measurements were also made on sodium and several of the organic cations at different concentrations. The relative permeabilities of the ions were found to be independent of concentration. Qualitatively, the permeability sequence for the Myxicola giant axon was similar to that of the frog node of Ranvier.

scholarly journals Chloride Fluxes in Isolated Dialyzed Barnacle Muscle Fibers

1972 ◽  
Vol 60 (4) ◽  
pp. 471-497 ◽  
Author(s):  
R. DiPolo
Keyword(s):  
Ph Dependence ◽  
Muscle Fibers ◽  
Membrane Conductance ◽  
Chloride Ions ◽  
Resting Potential ◽  
Constant Field ◽  
Ph Change ◽  
Decreasing Ph ◽  
Barnacle Muscle Fibers ◽  
External Ph

Chloride outflux and influx has been studied in single isolated muscle fibers from the giant barnacle under constant internal composition by means of a dialysis perfusion technique. Membrane potential was continually recorded. The chloride outfluxes and influxes were 143 and 144 pmoles/cm2-sec (mean resting potential: 58 mv, temperature: 22°–24°C) with internal and external chloride concentrations of 30 and 541 mM, respectively. The chloride conductance calculated from tracer measurements using constant field assumptions is about fourfold greater than that calculated from published electrical data. Replacing 97% of the external chloride ions by propionate reduces the chloride efflux by 51%. Nitrate ions applied either to the internal or external surface of the membrane slows the chloride efflux. The external pH dependence of the chloride efflux follows the external pH dependence of the membrane conductance, in the range pH 3.9–4.7, increasing with decreasing pH. In the range pH 5–9, the chloride efflux increased with increasing pH, in a manner similar to that observed in frog muscle fibers. The titration curve for internal pH changes in the range 4.0–7.0 was quantitatively much different from that for external pH change, indicating significant asymmetry in the internal and external pH dependence of the chloride efflux.

Potassium channel family in giant motor axons of Aglantha digitale

1993 ◽  
Vol 69 (3) ◽  
pp. 894-901 ◽  
Author(s):  
R. W. Meech ◽  
G. O. Mackie
Keyword(s):  
Ion Channels ◽  
Potassium Channels ◽  
Permeability Coefficient ◽  
Reversal Potential ◽  
Current Data ◽  
Constant Field ◽  
Motor Axons ◽  
Sodium Permeability ◽  
Fast Kinetics ◽  
Slow Kinetics

1. The simplicity of the jellyfish nervous system makes it an ideal preparation to assess the contributions of different ion channels to behavior. In the giant motor axons of the jellyfish Aglantha digitale, low-threshold spikes elicit slow swimming, whereas escape swimming depends on a higher-threshold, overshooting sodium-dependent action potential. At least three kinetically distinct transient potassium channels (fast, intermediate, and slow) are concerned with spike management in this preparation. 2. In situ recording with patch-clamp micropipettes from clusters of potassium channels provides a means of studying their properties in isolation. The three classes of ion channel were identified in ensemble current averages by their kinetics, their response to a conditioning prepulse and their voltage dependence. All three were highly selective for potassium, and the reversal potential of their unitary currents depended on the level of potassium used to fill the patch pipette. 3. A single potassium permeability coefficient (PK) calculated from the Goldman, Hodgkin, Katz “constant field” equation was used to fit unitary current data from all three channels in concentrations of external potassium < or = 500 mM. 4. Data from ensemble tail currents in seawater indicated that the sodium permeability coefficient (PNa) of channels with either intermediate or slow kinetics was < or = 0.015 PK; preliminary data from channels with fast kinetics suggested that they too had a PNa/PK selectivity of approximately 0.01. 5. We propose that spike management in the giant motor axons of Aglantha depends on three members of a family of potassium-selective ion channels that seem likely to be structurally related.

Extracellular H+ modulates acetylcholine-activated nonselective cation channels in guinea pig ileum

1995 ◽  
Vol 268 (1) ◽  
pp. C162-C170 ◽  
Author(s):  
R. Inoue ◽  
Y. Waniishi ◽  
Y. Ito
Keyword(s):  
Guinea Pig ◽  
Reversal Potential ◽  
Type Equation ◽  
Hill Coefficient ◽  
Patch Clamp Technique ◽  
Physiological Importance ◽  
Cationic Current ◽  
Whole Cell Patch Clamp ◽  
Pka Value ◽  
External Ph

The effects of external H+ on the acetylcholine-induced inward current (nonselective cationic current; InsACh) in guinea pig ileal smooth muscle were investigated using the conventional whole cell patch-clamp technique. When the external pH (pHo) was lowered, the amplitude of InsACh was increased, with no significant change in the reversal potential or no detectable induction of other ionic permeabilities. The dose-response curve for this effect was best described by a Hill-type equation with an apparent pKa value of 7.4 and a Hill coefficient of approximately 1. The effect of pHo was associated with a shift of the steady-state activation curve for InsACh; the half-maximum activation potential became more negative on lowering pHo. Similar results were obtained when InsACh was activated by intracellularly applied guanosine 5'-O-(3-thiotriphosphate). These results indicate that the external H+ activity is an efficient regulator of InsACh channel, and this may have a physiological importance for controlling the muscarinic receptor-mediated contractions in this muscle.

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