scholarly journals Contractile activation phenomena in voltage-clamped barnacle muscle fiber.

1978 ◽  
Vol 71 (5) ◽  
pp. 467-488 ◽  
Author(s):  
C Caputo ◽  
R Dipolo
Keyword(s):  
Membrane Potential ◽  
Equilibrium Potential ◽  
Tension Development ◽  
Barnacle Muscle ◽  
Time Integral ◽  
A Value ◽  
Tension Time ◽  
Contractile Activation ◽  
The Relationship ◽  
Barnacle Muscle Fibers

Tension development in voltage-clamped barnacle muscle fibers occurs with depolarizing pulses so small as not to activate the potassium and calcium conductance systems. Peak tension and the tension time integral appear to be graded by both amplitude and duration of the depolarizing pulses. Subthreshold depolarizing conditioning pulses shorter than 500 ms potentiate the response to a given test pulse. This effect diminishes and reverts when the duration of the conditioning pulse is increasingly prolonged. The relationship between fiber membrane potential and tension developed in response to depolarizing pulses is described by an S-shaped curve. The tension saturates at a membrane potential of about +10 mV (inside positive). For a given pulse duration the saturation value remains constant even when the fiber interior reaches a value of +230 mV, which is well above what may be estimated to be the equilibrium potential of calcium ions (Eca = +120). In the presence of 5 mM external procaine, the shape of the tension-potential curve changes; the maximum value tension besides being diminished is not sustained by falls when the potential approaches the estimated value for Eca. These results suggest that under physiological conditions the contractile activator is probably released from an internal store, and that the calcium entering the fiber as inward current does not play a direct major role in contractile activation.

Effects of calcium on membrane potential and sodium influx in barnacle muscle fibers

1983 ◽  
Vol 244 (3) ◽  
pp. C297-C302 ◽  
Author(s):  
S. S. Sheu ◽  
M. P. Blaustein
Keyword(s):  
Membrane Potential ◽  
Muscle Fibers ◽  
Cation Channels ◽  
Channel Blockers ◽  
Sodium Influx ◽  
Permeable Channel ◽  
Barnacle Muscle ◽  
Nonselective Cation Channels ◽  
Flux Measurements ◽  
Barnacle Muscle Fibers

The influence of internal and external Ca2+ on membrane potential and 22Na influx were tested in internally perfused giant barnacle muscle fibers. The fibers depolarized by about 2-3 mV, and Na+ influx increased when external Ca2+ was removed. These effects were inhibited and reversed by adding 2 mM La3+ externally but not by tetrodotoxin (TTX). Ca2+ channel blockers did not prevent the depolarization. Increasing internal free Ca2+ ([Ca2+]i) from 10(-7) to 10(-5) M also stimulated Na+ influx and depolarized the fibers by a few millivolts. Neither external La3+ nor TTX prevented the effects of raising [Ca2+]i; however, internal tetrabutylammonium ions depolarized the fibers and attenuated the internal Ca2+-dependent effects. These data are consistent with the idea that removal of external Ca2+ activates a La3+-sensitive channel that is permeable to Na+; raising [Ca2+]i activates a La2+-insensitive, Na+-permeable channel that may be similar to the internal Ca2+-activated nonselective cation channels observed in cardiac muscle. The results demonstrate that all Na+ (and Ca2+) fluxes that do not contribute to Na-Ca exchange must be carefully identified before the exchange stoichiometry can be determined from Na+ and Ca2+ flux measurements.

scholarly journals The effects of partial and selective reduction in the components of the proton-motive force on lactose uptake in Escherichia coli

1981 ◽  
Vol 200 (3) ◽  
pp. 583-589 ◽  
Author(s):  
S Ahmed ◽  
I R Booth
Keyword(s):  
Escherichia Coli ◽  
Steady State ◽  
Membrane Potential ◽  
Selective Reduction ◽  
Proton Motive Force ◽  
Motive Force ◽  
Ph Gradient ◽  
A Value ◽  
The Relationship ◽  
Lactose Transport

The relationship between the steady state lactose accumulation (delta plac) and the magnitude of the membrane potential (delta psi) and pH gradient (delta pH) has been studied at pHo5.5 and pHo7.5. An attempt has been made to differentiate between two possible means by which lactose accumulation may be reduced below the proton-motive force (delta p). Firstly, that delta psi and delta pH are not equivalent in driving lactose transport and secondly, that ‘slip’ reactions (beta-galactoside exit via the carrier without a proton) may reduce accumulation. The data support the latter; however, our conclusions are tempered by the observation that the apparent stoichiometry (delta plac/delta p) increases to a value of at least 2 at values of delta p below 130 mV.

scholarly journals Mechanisms of Anion and Cation Permeations in the Resting Membrane of a Barnacle Muscle Fiber

1971 ◽  
Vol 57 (4) ◽  
pp. 408-434 ◽  
Author(s):  
S. Hagiwara ◽  
K. Toyama ◽  
H. Hayashi
Keyword(s):  
Membrane Potential ◽  
Muscle Fiber ◽  
Ion Permeation ◽  
Monovalent Cations ◽  
Barnacle Muscle ◽  
Anion Permeation ◽  
Current Voltage ◽  
Ionic Conductances ◽  
The Relationship ◽  
Barnacle Muscle Fiber

The resting membrane of a barnacle muscle fiber is mostly permeable to cations in a solution of pH 7.7 whereas it becomes primarily permeable to anions if the pH is below 4.0. Mechanisms of ion permeation for various monovalent cations and anions were investigated at pH 7.7 and 3.9, respectively. Permeability ratios were obtained from the relationship between the membrane potential and the concentration of the test ions, and ionic conductances from current-voltage relations of the membrane. The permeability sequence for anions (SCN > I > NO3 > Br > ClO3 > Cl > BrO3 > IO3) was different from the conductance sequence for anions (Br, Cl > ClO3, NO3 > SCN). In contrast, the permeability and conductance sequences were identical for cations (K > Rb > Cs > Na > Li). The results suggest that anion permeation is governed by membrane charges while cation permeation is via some electrically neutral mechanism.

Mechanism of the Effect of Acetate on Frog Ventricular Muscle

1974 ◽  
Vol 52 (3) ◽  
pp. 404-423 ◽  
Author(s):  
Esther R. Anderson ◽  
J. G. Foulks
Keyword(s):  
Membrane Potential ◽  
Resting Membrane Potential ◽  
Acetate Solution ◽  
Tension Development ◽  
Electrogenic Transport ◽  
K Concentration ◽  
Reduced Rate ◽  
Induced Changes ◽  
The Relationship ◽  
Frog Ventricle

Substitution of acetate for external Cl produced a large persistent increase in the resting membrane potential (R.M.P.) of frog ventricle and a somewhat steeper relation between membrane potential (M.P.) and [K]o (external K concentration). An increased K conductance or reduced permeability to other ions could account for most of these results, but not for hyperpolarizations as great as −110 mV. Potentials of this size suggested a contribution from an active electrogenic transport system, but they were unaffected by several treatments including exposure to ouabain (10−7 M − 5 × 10−6 M), dinitrophenol (10−6 M, 10−5 M) or 30 mM tetraethylammonium.Acetate caused a prolongation of the action potential (A.P.) and a change in its configuration. Acetate also enhanced twitch tension and increased the rate of tension development. Similar changes are produced by removal of [K]o. The effects of both acetate and K removal on A.P. configuration were prevented by a reduced rate of stimulation.When acetate-induced hyperpolarization was reversed by raising [K]o to 10–15 mM, the configuration of the A.P. resembled that of controls and twitch tension did not increase. Thus, acetate-induced changes in the shape of the A.P. and in twitch tension appeared to be secondary to the increase in R.M.P. However, the relationship does not seem to be direct because these changes were temporary, whereas hyperpolarization was persistent.The character of the acetate-induced changes in A.P. configuration, and the dependence on stimulation rate and [Ca]o (external Ca concentration), suggested a raised [Ca]i (internal Ca concentration) and a possible increase in Ca influx. However, addition of Mn to the acetate solution did not prevent initial acetate-induced changes in the shape of the A.P. plateau and in twitch tension. Also in the absence of [Ca]o, disappearance of twitch tension was slowed by acetate. But acetate decreased the contracture tension produced in response to either increased [K]o or Na removal. Acetate may cause a redistribution of Ca within the cell.

A model for understanding membrane potential using springs

2005 ◽  
Vol 29 (4) ◽  
pp. 204-207 ◽  
Author(s):  
David L. Cardozo
Keyword(s):  
Membrane Potential ◽  
Simple Model ◽  
Cellular Membrane ◽  
Equilibrium Potential ◽  
Ionic Conductance ◽  
Similar Form ◽  
Ionic Equilibrium ◽  
Ionic Conductances ◽  
The Relationship

In this report, I present a simple model using springs to conceptualize the relationship between ionic conductances across a cellular membrane and their effect on membrane potential. The equation describing the relationships linking membrane potential, ionic equilibrium potential, and ionic conductance is of similar form to that describing the force generated by a spring as a function of its displacement. The spring analogy is especially useful in helping students to conceptualize the effects of multiple conductances on membrane potential.

Effects of ovariectomy on energy metabolism in exercising rat muscle studied by 31P-NMR

1989 ◽  
Vol 67 (5) ◽  
pp. 2060-2065 ◽  
Author(s):  
Z. Roth ◽  
Z. Argov ◽  
J. Maris ◽  
K. K. McCully ◽  
J. S. Leigh ◽  
...  
Keyword(s):  
Sex Hormones ◽  
Female Athletes ◽  
High Energy ◽  
Time Integral ◽  
Menopausal Women ◽  
Tension Time ◽  
Postexercise Recovery ◽  
Sciatic Nerve Stimulation ◽  
The Relationship

The effects of ovariectomy on metabolism of high-energy phosphate compounds during and after exercise were studied in hindleg muscles of 14 rats. Sciatic nerve stimulation was used to establish different work loads, and the changes in inorganic phosphate-to-phosphocreatine ratios (Pi/PCr) were recorded by 31P nuclear magnetic resonance (NMR) in vivo. Four weeks after ovariectomy, there was evidence of significantly higher Pi/PCr during work at stimulation rates greater than 0.5 Hz. The slope for the stimulation rate-to-Pi/PCr relationship decreased from 1.98 +/- 0.15 to 1.36 +/- 0.2 Hz/Pi/PCr after ovariectomy. The normalized tension output of these muscles, tested separately using identical stimulation protocols, was not changed with ovariectomy. Thus the relationship between work (tension-time integral) and bioenergetic cost (Pi/PCr) suggested reduced maximal enzyme activity (Vmax) by 9-17% as a result of lack of ovarian sex hormones, but no change in Michaelis-Menten constant (Km) was found. Postexercise recovery was also significantly slower (3.27 +/- 0.54 PCr/Pi units per minute compared with 4.04 +/- 1.08 in controls). It is suggested that reduced levels of ovarian sex hormones decrease oxidative phosphorylation. Cytochrome oxidase activity was reduced in these muscles by 40%, but other mitochondrial enzyme systems may be affected as well. The possible significance of these data is the implication of a reduced capacity for menopausal women or amenorrheic female athletes to perform prolonged intensive exercise.

Effects of amphotericin B on the electrical properties and electrolyte content of frog sartorius muscle

1980 ◽  
Vol 58 (9) ◽  
pp. 1138-1141 ◽  
Author(s):  
A. Coulombe ◽  
O. F. Schanne ◽  
I. Reisin ◽  
E. Ruiz-Ceretti
Keyword(s):  
Membrane Potential ◽  
Amphotericin B ◽  
Membrane Resistance ◽  
Equilibrium Potential ◽  
Sartorius Muscle ◽  
Sodium Permeability ◽  
A Value ◽  
Goldman Equation ◽  
Frog Sartorius ◽  
B 52

We studied the effect of amphotericin B (52 μM) on the membrane potential, membrane resistance, and intracellular Na+ and K+ concentrations in isolated frog sartorius muscles to characterize further the nature of the ionic conductance induced by the antibiotic. After 5 h of exposure to amphotericin B, the membrane depolarized from −89.9 to −51.0 mV, the membrane resistance decreased from 4537 to 907 Ωcm2, [K]i decreased from 122 to 31.2 mmol/L fiber H2O, and [Na]i increased from 30.9 to 88.7 mmol/L fiber H2O. The relative sodium permeability, PNa/PK, calculated with the Goldman equation remained apparently constant at a value of 0.01 in treated and untreated muscles. We hypothesize that amphotericin B creates either a nonselective cation channel or a completely nonselective ionic leak channel whose equilibrium potential is equal or close to the membrane potential.

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