Theoretical effects of transmembrane electroneutral exchange on membrane potential.

1. We used a modified voltage-clamp technique to measure the steady-state effective synaptic currents (I(N)) produced by activating four different input systems to cat hindlimb motoneurons: Ia afferent fibers, Ia-inhibitory interneurons, Renshaw interneurons, and contralateral rubrospinal neurons. In the same motoneurons, we measured the slope of the firing rate-injected current (f-I) relation in the primary range. We then reactivated these synaptic inputs during steady, repetitive firing to assess their effects on motoneuron discharge rate. 2. Our measurements of I(N) were derived from recordings made near the resting membrane potential, whereas the effects of the synaptic inputs on repetitive discharge were evaluated at more depolarized membrane potentials. Thus we adjusted the I(N) values for these changes in driving force based on estimates of the synaptic reversal potential and the mean membrane potential during repetitive discharge. 3. We found that changes in the steady-state discharge rate of a motoneuron produced by these synaptic inputs could be reasonably well predicted by the product of the estimated value of I(N) during repetitive firing and the slope of the motoneuron's f-I relation. Although there was a high correlation between predicted and observed changes in firing rate for our entire sample of motoneurons (r = 0.93; P < 0.001), the slope of the relation between predicted and observed firing rate modulation was significantly greater than 1. 4. The systematic difference between predicted and observed firing rate modulation observed in the overall sample was primarily due to the fact that our predictions underestimated the changes in firing rate produced by Ia excitation and Ia inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)

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Electrophysiological characterization of different types of neurons recorded in vivo in the motor cortex of the cat. II. Membrane parameters, action potentials, current-induced voltage responses and electrotonic structures

Journal of Neurophysiology ◽

10.1152/jn.1993.69.6.1865 ◽

1993 ◽

Vol 69 (6) ◽

pp. 1865-1879 ◽

Cited By ~ 48

Author(s):

A. Baranyi ◽

M. B. Szente ◽

C. D. Woody

Keyword(s):

Steady State ◽

Membrane Potential ◽

Motor Cortex ◽

Action Potential ◽

Action Potentials ◽

Cell Types ◽

Type I ◽

Firing Threshold ◽

Current Pulses ◽

Different Types

1. Electrical properties of four functional classes [inactivating bursting (ib), noninactivating bursting (nib), fast spiking (fsp), and regular spiking (rsp)] of neurons in the motor cortex of conscious cats were studied with the use of intracellular voltage recording and single-electrode voltage-clamp (SEVC) techniques. Evaluations were made of action potentials and afterpotentials, current-voltage (I-V) relationships, and passive cable properties. Values of membrane potential (Vm), input resistance (RN), membrane time constant (T0), and firing threshold (T50) were also measured. The data were used to extend the electrophysiological classifications of neurons described in the companion paper. 2. Average values of Vm (from -63 to -66 mV), action-potential amplitudes (from 72 to 77 mV), and firing threshold (-54 mV) were not statistically different in different types of neurons. However, the magnitude of intracellularly injected depolarizing current required to induce spike discharge at 50% probability varied significantly (from 0.6 to 1.1 nA) among cell types. The mean RN and T0 measured at Vm varied between 8.3 and 19.8 M omega, and 7.2 and 15.1 ms, respectively, in the cell classes. 3. Action potentials were overshooting. Their mean duration at half amplitude varied from 0.25 to 0.73 ms among different cell types. Three types of action-potential configurations were distinguished. Type I action potentials found in nib and rsp neurons were relatively fast and had a depolarizing afterpotential (DAP) as well as fast and slow after hyperpolarizations (fAHPs, sAHPs). Type II action potentials found in ib and rsp cells had relatively slow rise and decay phases, DAPs, and sAHPs. Their fAHPs were small or absent. Type III action potentials were found exclusively in fsp cells, had very short durations, prominent fAHPs, but no sAHPs. 4. Steady-state I-V relationships were determined by measuring voltage responses to 0.2- to 1.0-nA hyperpolarizing, rectangular current pulses at different membrane potentials. Both RN and T0 exhibited nonlinear behavior over wide ranges of membrane potential; however, between -65 and -75 mV, the I-V relationships varied little, and they appeared constant in most cells. The steady-state values of RN increased with decreasing, and decreased with increasing the membrane potential in all but fsp cells. The I-V relationships were virtually linear in fsp neurons. 5. Transient I-V relationships were studied by measuring voltage responses to depolarizing and hyperpolarizing, rectangular current pulses of increasing amplitude from a preset membrane potential of -70 mV.(ABSTRACT TRUNCATED AT 400 WORDS)

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The interplay of seven subthreshold conductances controls the resting membrane potential and the oscillatory behavior of thalamocortical neurons

Journal of Neurophysiology ◽

10.1152/jn.00647.2013 ◽

2014 ◽

Vol 112 (2) ◽

pp. 393-410 ◽

Cited By ~ 24

Author(s):

Yimy Amarillo ◽

Edward Zagha ◽

German Mato ◽

Bernardo Rudy ◽

Marcela S. Nadal

Keyword(s):

Steady State ◽

Membrane Potential ◽

Computational Model ◽

Potassium Current ◽

Brain Slices ◽

Reversal Potential ◽

Burst Firing ◽

Resting Membrane Potential ◽

Cationic Current ◽

Steady State Current

The signaling properties of thalamocortical (TC) neurons depend on the diversity of ion conductance mechanisms that underlie their rich membrane behavior at subthreshold potentials. Using patch-clamp recordings of TC neurons in brain slices from mice and a realistic conductance-based computational model, we characterized seven subthreshold ion currents of TC neurons and quantified their individual contributions to the total steady-state conductance at levels below tonic firing threshold. We then used the TC neuron model to show that the resting membrane potential results from the interplay of several inward and outward currents over a background provided by the potassium and sodium leak currents. The steady-state conductances of depolarizing Ih (hyperpolarization-activated cationic current), IT (low-threshold calcium current), and INaP (persistent sodium current) move the membrane potential away from the reversal potential of the leak conductances. This depolarization is counteracted in turn by the hyperpolarizing steady-state current of IA (fast transient A-type potassium current) and IKir (inwardly rectifying potassium current). Using the computational model, we have shown that single parameter variations compatible with physiological or pathological modulation promote burst firing periodicity. The balance between three amplifying variables (activation of IT, activation of INaP, and activation of IKir) and three recovering variables (inactivation of IT, activation of IA, and activation of Ih) determines the propensity, or lack thereof, of repetitive burst firing of TC neurons. We also have determined the specific roles that each of these variables have during the intrinsic oscillation.

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Loss-of-function and gain-of-function phenotypes of stomatocytosis mutant RhAG F65S

AJP Cell Physiology ◽

10.1152/ajpcell.00054.2011 ◽

2011 ◽

Vol 301 (6) ◽

pp. C1325-C1343 ◽

Cited By ~ 17

Author(s):

Andrew K. Stewart ◽

Boris E. Shmukler ◽

David H. Vandorpe ◽

Alicia Rivera ◽

John F. Heneghan ◽

...

Keyword(s):

Steady State ◽

Membrane Potential ◽

Xenopus Oocytes ◽

Cellular Responses ◽

Transport Mechanisms ◽

Loss Of Function ◽

Wild Type ◽

Gain Of Function ◽

Cation Conductance ◽

Methylammonium Chloride

Four patients with overhydrated cation leak stomatocytosis (OHSt) exhibited the heterozygous RhAG missense mutation F65S. OHSt erythrocytes were osmotically fragile, with elevated Na and decreased K contents and increased cation channel-like activity. Xenopus oocytes expressing wild-type RhAG and RhAG F65S exhibited increased ouabain and bumetanide-resistant uptake of Li+and86Rb+, with secondarily increased86Rb+influx sensitive to ouabain and to bumetanide. Increased RhAG-associated14C-methylammonium (MA) influx was severely reduced in RhAG F65S-expressing oocytes. RhAG-associated influxes of Li+,86Rb+, and14C-MA were pharmacologically distinct, and Li+uptakes associated with RhAG and RhAG F65S were differentially inhibited by NH4+and Gd3+. RhAG-expressing oocytes were acidified and depolarized by 5 mM bath NH3/NH4+, but alkalinized and depolarized by subsequent bath exposure to 5 mM methylammonium chloride (MA/MA+). RhAG F65S-expressing oocytes exhibited near-wild-type responses to NH4Cl, but MA/MA+elicited attenuated alkalinization and strong hyperpolarization. Expression of RhAG or RhAG F65S increased steady-state cation currents unaltered by bath Li+substitution or bath addition of 5 mM NH4Cl or MA/MA+. These oocyte studies suggest that 1) RhAG expression increases oocyte transport of NH3/NH4+and MA/MA+; 2) RhAG F65S exhibits gain-of-function phenotypes of increased cation conductance/permeability, and loss-of-function phenotypes of decreased and modified MA/MA+transport, and decreased NH3/NH4+-associated depolarization; and 3) RhAG transports NH3/NH4+and MA/MA+by distinct mechanisms, and/or the substrates elicit distinct cellular responses. Thus, RhAG F65S is a loss-of-function mutation for amine transport. The altered oocyte intracellular pH, membrane potential, and currents associated with RhAG or RhAG F65S expression may reflect distinct transport mechanisms.

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Acidification of rat liver lysosomes: quantitation and comparison with endosomes

AJP Cell Physiology ◽

10.1152/ajpcell.1993.265.4.c901 ◽

1993 ◽

Vol 265 (4) ◽

pp. C901-C917 ◽

Cited By ~ 42

Author(s):

R. W. Van Dyke

Keyword(s):

Steady State ◽

Membrane Potential ◽

Rat Liver ◽

Proton Pumps ◽

Intact Cells ◽

Early Endosomes ◽

Medium Permeability ◽

Electrogenic Proton Pump ◽

Secondary Lysosomes ◽

Permeability Studies

Both lysosomes and endosomes are acidified by an electrogenic proton pump, although studies in intact cells indicate that the steady-state internal pH (pHi) of lysosomes is more acid than that of endosomes. We undertook the present study to examine in detail the acidification mechanism of purified rat liver secondary lysosomes and to compare it with that of a population of early endosomes. Both endosomes and lysosomes exhibited ATP-dependent acidification, but proton influx rates were 2.4- to 2.7-fold greater for endosomes than for lysosomes because of differences in both buffering capacity and acidification rates, suggesting that endosomes exhibited greater numbers or rates of proton pumps. Lysosomes, however, exhibited a more acidic steady-state pHi due in part to a slower proton leak rate. Changes in medium Cl- increased acidification rates of endosomes more than lysosomes, and the lysosome ATP-dependent interior-positive membrane potential was only partially eliminated by high-Cl- medium. Permeability studies suggested that lysosomes were less permeable to Na+, Li+, and Cl- and more permeable to K+ and PO4(2-) than endosomes. Na-K-adenosine-triphosphatase did not appear to regulate acidification of either vesicle type. Endosome and lysosome acidification displayed similar inhibition profiles to N-ethylmaleimide, dicyclohexyl-carbodiimide, and vanadate, although lysosomes were somewhat more sensitive [concentration producing 50% maximal inhibition (IC50) 1 nM] to bafilomycin A1 than endosomes (IC50 7.6 nM). Oligomycin (1.5-3 microM) stimulated lysosome acidification due to shunting of membrane potential. Overall, acidification of endosomes and lysosomes was qualitatively similar but quantitatively somewhat different, possibly related to differences in the density or rate of proton pumps as well as vesicle permeability to protons, anions, and other cations.

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The anterior and posterior ‘stomach’ regions of larval Aedes aegypti midgut: regional specialization of ion transport and stimulation by 5-hydroxytryptamine

Journal of Experimental Biology ◽

10.1242/jeb.202.3.247 ◽

1999 ◽

Vol 202 (3) ◽

pp. 247-252 ◽

Cited By ~ 14

Author(s):

T.M. Clark ◽

A. Koch ◽

D.F. Moffett

Keyword(s):

Steady State ◽

Aedes Aegypti ◽

Ion Transport ◽

Malpighian Tubules ◽

Transport Mechanisms ◽

Regional Specialization ◽

Negative Deflection ◽

Electrical Polarity

The ‘stomach’ region of the larval mosquito midgut is divided into histologically distinct anterior and posterior regions. Anterior stomach perfused symmetrically with saline in vitro had an initial transepithelial potential (TEP) of −66 mV (lumen negative) that decayed within 10–15 min to a steady-state TEP near −10 mV that was maintained for at least 1 h. Lumen-positive TEPs were never observed in the anterior stomach. The initial TEP of the perfused posterior stomach was opposite in polarity, but similar in magnitude, to that of the anterior stomach, measuring +75 mV (lumen positive). This initial TEP of the posterior stomach decayed rapidly at first, then more slowly, eventually reversing the electrical polarity of the epithelium as lumen-negative TEPs were recorded in all preparations within 70 min. Nanomolar concentrations of the biogenic amine 5-hydroxytryptamine (5-HT, serotonin) stimulated both regions, causing a negative deflection of the TEP of the anterior stomach and a positive deflection of the TEP of the posterior stomach. Phorbol 12,13-diacetate also caused a negative deflection of the TEP of the anterior stomach, but had no effect on the TEP of the posterior stomach. These data demonstrate that 5-HT stimulates region-specific ion-transport mechanisms in the stomach of Aedes aegypti and suggest that 5-HT coordinates the actions of the Malpighian tubules and midgut in the maintenance of an appropriate hemolymph composition in vivo.

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Electrogenic Na+ Transport in a Crustacean Coxal Receptor

Journal of Experimental Biology ◽

10.1242/jeb.78.1.29 ◽

1979 ◽

Vol 78 (1) ◽

pp. 29-45

Author(s):

MAURIZIO MIROLLI

Keyword(s):

Steady State ◽

Membrane Potential ◽

Input Resistance ◽

Scylla Serrata ◽

Partial Action ◽

State Response ◽

Electrogenic Na Pump ◽

K Concentration ◽

Low K ◽

In Cells

1. The response of the coxal receptors of the crab Scylla serrata to step stretches consisted of a partial action potential, Vα, followed by a steady-state depolarization, V8. The input resistance of the fibre was reduced during V8. 2. In the absence of stimulation, the dendrites of the receptors depolarized when external Na+ was substituted with choline or Li+, and when the external K+ concentration was increased or decreased. The dendrites also depolarized when ouabain was added to the saline. 3. The amplitude of both Vα and V8 was dependent on external Na+. In cells which were depolarized by ouabain, the amplitude of V8 increased when the K+ concentration of the saline was reduced. 4. V8 was followed by a small, but long-lasting, after-potential which was depolarizing when the membrane potential was between −70 and −60 mV. In cells depolarized by ouabain or by low K+ saline, the after-potential became hyperpolarizing. 5. When trains of brief stretches (each 5 ms in duration) were used as stimuli, the cells responded with trains of Vα responses. During this tetanic stimulation the cells hyperpolarized; cessation of the stimulus train was followed by a long-lasting hyperpolarization (PTH). 6. PTH was abolished in Li+ saline, in low K+ saline, and in the presence of ouabain. In control or in low K+ saline, PTH was not accompanied by a decrease in the input resistance of the fibres. 7. It is concluded that an electrogenic Na+ pump (or equivalent process) contributes a substantial fraction of the membrane potential of the unstimulated coxal receptors. Pump activity could be increased by Na+-loading the distal part of the cells with trains of Vα responses. By contrast, during the steady-state response to stretch, the pump was not activated.

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Characterization of synaptically mediated fast and slow inhibitory processes in piriform cortex in an in vitro slice preparation

Journal of Neurophysiology ◽

10.1152/jn.1988.59.5.1352 ◽

1988 ◽

Vol 59 (5) ◽

pp. 1352-1376 ◽

Cited By ~ 78

Author(s):

G. F. Tseng ◽

L. B. Haberly

Keyword(s):

Membrane Potential ◽

Piriform Cortex ◽

Reversal Potential ◽

Pyramidal Cells ◽

Membrane Depolarization ◽

Resting Membrane Potential ◽

Excitatory Postsynaptic Potential ◽

Pentobarbital Sodium ◽

Postsynaptic Potential ◽

Conductance Increase

1. Intracellular recordings were obtained from anatomically verified layer II pyramidal cells in slices from rat piriform cortex cut perpendicular to the surface. 2. Responses to afferent and association fiber stimulation at resting membrane potential consisted of a depolarizing potential followed by a late hyperpolarizing potential (LHP). Membrane polarization by current injection revealed two components in the depolarizing potential: an initial excitatory postsynaptic potential (EPSP) followed at brief latency by an inhibitory postsynaptic potential (IPSP) that inverted with membrane depolarization and truncated the duration of the EPSP. 3. The early IPSP displayed the following characteristics suggesting mediation by gamma-aminobutyric acid (GABA) receptors linked to Cl- channels: associated conductance increase, sensitivity to increases in internal Cl- concentration, blockage by picrotoxin and bicuculline, and potentiation by pentobarbital sodium. The reversal potential was in the depolarizing direction with respect to resting membrane potential so that the inhibitory effect was exclusively via current shunting. 4. The LHP had an associated conductance increase and a reversal potential of -90 mV in normal bathing medium that shifted according to Nernst predictions for a K+ potential with changes in external K+ over the range 4.5-8 mM indicating mediation by the opening of K+ channels and ruling out an electrogenic pump origin. 5. Lack of effect of bath-applied 8-bromoadenosine 3',5'-cyclic monophosphate (8-Br-cAMP) or internally applied ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) on the LHP and failure of high amplitude, direct membrane depolarization to evoke a comparable potential, argue against endogenous mediation of the LHP by a Ca2+ activated K+ conductance [gK(Ca)]. However, an apparent endogenously mediated gK(Ca) with a duration much greater than the LHP was observed in a low percent of layer II pyramidal cells. Lack of effect of 8-Br-cAMP also indicates a lack of dependence of the LHP on cAMP. 6. Other characteristics of the LHP that were demonstrated include: a lack of blockage by GABAA receptor antagonists, a probable voltage sensitivity (decrease in amplitude in the depolarizing direction), and an apparent brief onset latency (less than 10 ms) when the early IPSP was blocked by picrotoxin. The LHP was unaffected by pentobarbital sodium when the early IPSP was blocked by picrotoxin. 7. Both the LHP and early IPSP were blocked by low Ca2+/high Mg2+, consistent with disynaptic mediation.(ABSTRACT TRUNCATED AT 400 WORDS)

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Voltage dependence of chloride current through Xenopus muscle membrane in alkaline solutions

Canadian Journal of Physiology and Pharmacology ◽

10.1139/y80-153 ◽

1980 ◽

Vol 58 (9) ◽

pp. 999-1010 ◽

Cited By ~ 6

Author(s):

Peter C. Vaughan ◽

James G. McLarnon ◽

Donald D. F. Loo

Keyword(s):

Steady State ◽

Membrane Potential ◽

Chloride Conductance ◽

Resting Potential ◽

Muscle Membrane ◽

Alkaline Solutions ◽

Constant Field ◽

Confined Space ◽

Initial Current ◽

Test Current

Three-microelectrode voltage-clamp experiments have been conducted on surface fibres of Xenopus laevis sartorius muscles. When potassium and chloride were substituted by rubidium and sulphate, negligibly small currents were observed. In solutions containing rubidium and chloride at pH 8.4–8.8 normally polarized fibres exhibited instantaneous current–voltage relations that were linear over a wide voltage range. Chloride conductance varied widely from fibre to fibre; the mean resting conductance at −80 mV was 7.4 × 10−4 ± 2.6 × 10−4 S/cm2 (mean ± SE). When hyperpolarizing voltage steps were made, conductance declined from the initial to the steady state; inward currents saturated near 14 μA/cm2. In experiments performed on fibres depolarized by immersion in K+-and Rb+-rich solutions it was found that resting conductance did not increase by as much as would be expected from constant field – constant permeability precepts, by comparison with normally polarized fibres. Despite the low chloride transmembrane concentration ratio, rectification in the steady state was similar in depolarized and normally polarized fibres.When a two-pulse protocol was employed to test the availability of chloride conductance after conditioning of the system at some voltage, it was found that the test current, the initial current at the onset of the test voltage step, depended sigmoidally on the conditioning voltage. The sigmoid relationships had asymptotic limits: after hyperpolarizing conditioning the test current was minimal, after depolarizing conditioning, maximal. Normalized sigmoid relations were superimposable, whether from normally polarized or chronically depolarized cells.When the protocol was repeated using different test potentials and initial currents following a particular conditioning voltage were plotted against the test potential, families of straight lines were obtained. The slopes of the members of these families were dependent on the conditioning voltage: the more negative the conditioning step the lower the slope. The lines projected through a mutual intersection at a voltage slightly more positive than the resting potential. This is interpreted as indicating that there is some voltage, slightly positive with respect to the membrane potential, at which the initial current is independent of the conditioning voltage.It is concluded that the state of the chloride conductance mechanism is a function of the deviation of the membrane from the resting potential rather than of the absolute membrane potential and that relaxations from initial to steady states reflect properties of the permeation mechanism rather than accumulation or depletion of chloride in a confined space, although some contribution by a mechanism such as the latter cannot be completely ruled out.

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