Repriming of delayed potassium conductance in frog skeletal muscle

1980 ◽  
Vol 87 (1) ◽  
pp. 217-228
Author(s):  
E. W. Ballou
Keyword(s):  
Skeletal Muscle ◽  
Time Course ◽  
Rana Pipiens ◽  
Voltage Dependence ◽  
Potassium Conductance ◽  
Frog Skeletal Muscle ◽  
Semitendinosus Muscle ◽  
Sequential Model ◽  
Temperature Dependences ◽  
High Concentrations

A dissection of the semitendinosus muscle from Rana pipiens was developed for three-microelectrode voltage-clamp studies of the delayed potassium-selective conductance system. The delayed conductance inactivates in muscles bathed in high concentrations of potassium or rubidium, but can be reprimed by hyperpolarizing voltage pulses to membrane potentials beyond −80 mV. The repriming time-course was studied by measuring the delayed conductance that coulde be activated following hyperpolarizing pulses of varying duration. Responses following 20–100 s pulses to potentials between −90 and −140 mV could not be reconciled with an exponential approach to the conductance present in normally polarized fibres. The sigmoid appearance of the early (< 25 s) time course was exaggerated by cooling from 20 to 10 degrees C. This effect was described by a sequential model invoking two inactivated states with different temperature dependences. An explanation is suggested for differences in the kinetics and voltage dependence of repriming between briefly and chronically depolarized muscle cells.

scholarly journals Altered sodium and gating current kinetics in frog skeletal muscle caused by low external pH.

1984 ◽  
Vol 84 (5) ◽  
pp. 771-788 ◽  
Author(s):  
D T Campbell ◽  
R Hahin
Keyword(s):  
Skeletal Muscle ◽  
Time Constant ◽  
Time Course ◽  
Voltage Dependence ◽  
Low Ph ◽  
Na Channel ◽  
Frog Skeletal Muscle ◽  
Gating Current ◽  
Gating Charge ◽  
External Ph

The effect of low pH on the kinetics of Na channel ionic and gating currents was studied in frog skeletal muscle fibers. Lowering external pH from 7.4 to 5.0 slows the time course of Na current consistent with about a +25-mV shift in the voltage dependence of activation and inactivation time constants. Similar shifts in voltage dependence adequately describe the effects of low pH on the tail current time constant (+23.3 mV) and the gating charge vs. voltage relationship (+22.1 mV). A significantly smaller shift of +13.3 mV described the effect of pH 5.0 solution on the voltage dependence of steady state inactivation. Changes in the time course of gating current at low pH were complex and could not be described as a shift in voltage dependence. tau g, the time constant that describes the time course of the major component of gating charge movement, was slowed in pH 5.0 solution by a factor of approximately 3.5 for potentials from -60 to +45 mV. We conclude that the effects of low pH on Na channel gating cannot be attributed simply to a change in surface potential. Therefore, although it may be appropriate to describe the effect of low pH on some Na channel kinetic properties as a "shift" in voltage dependence, it is not appropriate to interpret such shifts as a measure of changes in surface potential. The maximum gating charge elicited from a holding potential of -150 mV was little affected by low pH.(ABSTRACT TRUNCATED AT 250 WORDS)

Hg2+-induced contracture in mechanically skinned fibers of frog skeletal muscle

1985 ◽  
Vol 63 (9) ◽  
pp. 1070-1074 ◽  
Author(s):  
Takako Aoki ◽  
Toshiharu Oba ◽  
Ken Hotta
Keyword(s):  
Skeletal Muscle ◽  
Sarcoplasmic Reticulum ◽  
Sulfhydryl Groups ◽  
Skinned Fibers ◽  
Frog Skeletal Muscle ◽  
Semitendinosus Muscle ◽  
Skinned Fiber ◽  
Brij 58 ◽  
Develop Tension

In mechanically skinned fibers of the semitendinosus muscle of bullfrogs, we examined the role of membrane sulfhydryl groups on Ca2+ release from the sarcoplasmic reticulum (SR). Hg2+, a sulfhydryl reagent (20–100 μM), induced a repetitive contracture of skinned fibers, and this contracture did not occur in skinned fibers in which the SR had been disrupted by treatment with a detergent (Brij 58). Procaine (10 mM), Mg2+ (5 mM), or dithiothreitol (1 mM) blocked the Hg2+-induced contracture. Ag+ or p-chloromercuribenzenesulfonic acid produced similar contractures to that induced by Hg2+. We conclude that Hg2+ releases Ca2+ from SR of a skinned fiber by modifying sulfhydryl groups on the SR membrane, and suggest that the Ca2+ released by Hg2+ may trigger a greater release of Ca2+ from SR to develop tension.

Parvalbumin relaxes frog skeletal muscle when sarcoplasmic reticulum Ca(2+)-ATPase is inhibited

1996 ◽  
Vol 270 (2) ◽  
pp. C411-C417 ◽  
Author(s):  
Y. Jiang ◽  
J. D. Johnson ◽  
J. A. Rall
Keyword(s):  
Skeletal Muscle ◽  
Sarcoplasmic Reticulum ◽  
Relaxation Rate ◽  
Time Course ◽  
Muscle Fibers ◽  
Peak Force ◽  
Half Time ◽  
Frog Skeletal Muscle ◽  
Twitch Force ◽  
Total Failure

Inhibition of sarcoplasmic reticulum (SR) Ca(2+)-adenosinetriphosphatase (ATPase) with 2,5-di-(tert-butyl)-1,4-benzohydroquinone (TBQ) in frog skeletal muscle fibers at 10 degrees C prolonged the half time of the fall of the Ca2+ transient by 62% and twitch force by 100% and increased peak force by 120% without increasing the amplitude of the Ca2+ signal. In the presence of TBQ the rate of relaxation and the rate of fall of Ca2+ became progressively slower in a series of twitches until relaxation failed. Relaxation rate decreased with a time course (approximately 2 s-1) similar to the Mg2+ off rate from purified parvalbumin (PA; 3.6 s-1). TBQ slowed the rate of fall of Ca2+ (5-fold) and force (8-fold) in a 0.3-s tetanus so that the rate of fall of Ca2+ (approximately 2.5 s-1) was similar to the Mg2+ off rate from PA. TBQ caused a near total failure of both Ca2+ sequestration and relaxation in a 1.1-s tetanus, during which PA would be saturated with Ca2+ and could not contribute to relaxation. Thus, when the SR Ca(2+)-ATPase is inhibited, Mg(2+)-PA can sequester Ca2+ and produce relaxation at a rate that is defined by the Mg2+ off rate from PA.

scholarly journals Sodium channel gating currents in frog skeletal muscle.

1983 ◽  
Vol 82 (5) ◽  
pp. 679-701 ◽  
Author(s):  
D T Campbell
Keyword(s):  
Skeletal Muscle ◽  
Sodium Channel ◽  
Time Course ◽  
Channel Gating ◽  
Total Charge ◽  
Charge Movement ◽  
Frog Skeletal Muscle ◽  
Gating Currents ◽  
Gating Mechanism ◽  
Charge Movements

Charge movements similar to those attributed to the sodium channel gating mechanism in nerve have been measured in frog skeletal muscle using the vaseline-gap voltage-clamp technique. The time course of gating currents elicited by moderate to strong depolarizations could be well fitted by the sum of two exponentials. The gating charge exhibits immobilization: at a holding potential of -90 mV the proportion of charge that returns after a depolarizing prepulse (OFF charge) decreases with the duration of the prepulse with a time course similar to inactivation of sodium currents measured in the same fiber at the same potential. OFF charge movements elicited by a return to more negative holding potentials of -120 or -150 mV show distinct fast and slow phases. At these holding potentials the total charge moved during both phases of the gating current is equal to the ON charge moved during the preceding prepulse. It is suggested that the slow component of OFF charge movement represents the slower return of charge "immobilized" during the prepulse. A slow mechanism of charge immobilization is also evident: the maximum charge moved for a strong depolarization is approximately doubled by changing the holding potential from -90 to -150 mV. Although they are larger in magnitude for a -150-mV holding potential, the gating currents elicited by steps to a given potential have similar kinetics whether the holding potential is -90 or -150 mV.

Quantitative x-ray elemental imaging in stimulated single intact skeletal muscle fibers: The fate of calcium in the presence of ryanodine

1988 ◽  
Vol 46 ◽  
pp. 90-91
Author(s):  
J. Sommer ◽  
P. Ingram ◽  
A. LeFurgey ◽  
R. Nassar ◽  
T. High
Keyword(s):  
Skeletal Muscle ◽  
Electrical Stimulation ◽  
Time Course ◽  
Imaging System ◽  
Quantitative Imaging ◽  
Muscle Fibers ◽  
Frog Skeletal Muscle ◽  
X Ray ◽  
Skeletal Muscle Fibers ◽  
Freeze Dried

We are involved in a continuing series of experiments aimed at a complete description,in terms of morphology and quantitative topochemistry, of the time course of spatial distributions of physiologically important elements during excitation-contraction coupling (ECC) at different time intervals (fractions of msec) following electrical stimulation of single, intact frog skeletal muscle fibers. In this present study wg report such distributions for Ca after 1,2 and 3 min of electrical stimulation in the presence of 2x10-4 M ryanodine, an alkaloid that, in time, causes irreversible muscle contractures.Single, intact frog skeletal muscle fibers were quick-frozen, cryosectioned, freeze-substituted and in one case freeze-fractured. The freeze-dried cryosections were subjected to electron probe X-ray microanalysis (EPXMA) in a JEOL 1200EX analytical electron microscope equipped with a Tracor Northern X-ray detector and a fully quantitative imaging system. Both, 64/64 pixel images (ambient temp.), and small raster probes (cold stage,-115 °C) for better statistics, were obtained, each from the same section.

scholarly journals A quantitative study of potassium channel kinetics in rat skeletal muscle from 1 to 37 degrees C.

1983 ◽  
Vol 81 (4) ◽  
pp. 485-512 ◽  
Author(s):  
K G Beam ◽  
P L Donaldson
Keyword(s):  
Skeletal Muscle ◽  
Low Temperatures ◽  
Time Course ◽  
Voltage Dependence ◽  
Potassium Currents ◽  
Effect Of Temperature ◽  
Time Axis ◽  
Rat Skeletal Muscle ◽  
Rapid Phase ◽  
Qualitative Effect

Potassium currents were measured using the three-microelectrode voltage-clamp technique in rat omohyoid muscle at temperatures from 1 to 37 degrees C. The currents were fitted according to the Hodgkin-Huxley equations as modified for K currents in frog skeletal muscle (Adrian et al., 1970a). The equations provided an approximate description of the time course of activation, the voltage dependence of the time constant of activation (tau n), and the voltage dependence of gK infinity. At higher temperatures the relationship between gK infinity and voltage was shifted in the hyperpolarizing direction. The effect of temperature on tau n was much greater in the cold than in the warm: tau n had a Q10 of nearly 6 at temperatures below 10 degrees C, but a Q10 of only approximately 2 over the range of 30-38 degrees C. The decreasing dependence of tau n on temperature was gradual and the Arrhenius plot of tau n revealed no obvious break-points. In addition to its quantitative effect on activation kinetics, temperature also had a qualitative effect. Near physiological temperatures (above approximately 25 degrees C), the current was well described by n4 kinetics. At intermediate temperatures (approximately 15-25 degrees C), the current was well described by n4 kinetics, but only if the n4 curve was translated rightward along the time axis (i.e., the current had a greater delay than could be accounted for by simple n4 kinetics). At low temperatures (below approximately 15 degrees C), n4 kinetics provided only an approximate fit whether or not the theoretical curve was translated along the time axis. In particular, currents in the cold displayed an initial rapid phase of activation followed by a much slower one. Thus, low temperatures appear to reveal steps in the gating process which are kinetically "hidden" at higher temperatures. Taken together, the effects of temperature on potassium currents in rat skeletal muscle demonstrate that the behavior of potassium channels at physiological temperatures cannot be extrapolated, either quantitatively or qualitatively, from experiments carried out in the cold.

Role of Parvalbumin in Skeletal Muscle Relaxation

Physiology ◽  
1996 ◽  
Vol 11 (6) ◽  
pp. 249-255 ◽  
Author(s):  
JA Rall
Keyword(s):  
Skeletal Muscle ◽  
Skeletal Muscles ◽  
Muscle Relaxation ◽  
Calcium Pump ◽  
Frog Skeletal Muscle ◽  
Animal Kingdom ◽  
Calcium Buffer ◽  
High Concentrations ◽  
Sarcoplasmic Reticulum Calcium

Parvalbumin, a soluble intracellular calcium buffer, is present in high concentrations in fast-contracting skeletal muscles across the animal kingdom. In frog skeletal muscle, pharmacological or low-temperature inhibition of the sarcoplasmic reticulum calcium pump reveals that parvalbumin sequesters calcium and promotes relaxation at a rate determined by magnesium dissociation from parvalbumin.

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