Electro-mediated damage in the narrowest pore of voltage-gated K channels in frog skeletal muscle membrane

Exposure of frog toe muscles to 1 mM La3+ results in a decrease in amplitude and rate of tension development of potassium contractures and twitches. At this concentration La3+ also inhibits the uptake of calcium, both in the resting condition and during stimulation. Caffeine contractures are unaffected even after a 5-min pre-exposure to La3+. The depolarization induced by various concentrations of K+ is reduced by about 10 mV as is the amplitude of the action potential. The rate of rise of the action potential is reduced by about 40% after 1 min in La3+ Ringer. Neither the decreased amplitude nor the reduced rate of depolarization is considered to be sufficient to explain the inhibition of tension development. It is suggested that La3+ partially uncouples excitation from contraction by preventing the release of a trigger-Ca2+ fraction from some site on the muscle membrane. This fraction normally plays a role in excitation–contraction coupling, although some tension may still be developed in the absence of a trigger-Ca2+ influx.

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Membrane domain localization of pH-regulating transporters in frog skeletal muscle membrane vesicles

AJP Cell Physiology ◽

10.1152/ajpcell.1996.271.4.c1367 ◽

1996 ◽

Vol 271 (4) ◽

pp. C1367-C1379 ◽

Cited By ~ 2

Author(s):

R. W. Putnam ◽

P. B. Douglas ◽

N. A. Ritucci

Keyword(s):

Skeletal Muscle ◽

Atpase Activity ◽

Surface Membrane ◽

Membrane Vesicles ◽

Muscle Membrane ◽

Frog Skeletal Muscle ◽

Membrane Domain ◽

Ph Response ◽

Kinase C ◽

Inside Out

The distribution of pH-regulating transporters in surface and transverse (T) tubular membrane (TTM) domains of frog skeletal muscle was studied. 2',7'-Bis(carboxyethyl)-5(6)- carboxyfluorescein-loaded giant sarcolemmal vesicles, containing surface membrane, exhibited reversible Na+/H+ exchange. A microsomal vesicle fraction was shown to be enriched in TTM on the basis of high Na(+)-K(+)-ATPase and Mg(2+)-ATPase activity, high ouabain and nitrendipine binding, and low Ca(2+)-ATPase activity. TTM vesicles were well sealed and oriented inside out. Vesicles were loaded with the pH-sensitive dye pyranine. In response to an inwardly directed Na+ gradient, vesicles displayed virtually no alkalinization unless monensin was present. No pH response to an imposed Na+ gradient was seen regardless of the direction of the pH gradient across the vesicles, after phosphorylation of the vesicles with protein kinase C, or when exposed to guanosine 5'-O-(3-thiotriphosphate). In the presence of CO2, addition of Na+ or Cl- had no effect on vesicle pH. These data indicate that the TTM lacks functional pH-regulating transporters [Na+/H+ and (Na+ + HCO3-)/Cl- exchangers], suggesting that pH-regulating transporters are localized only to the surface membrane domain in frog muscle.

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High-affinity [3H]PN200-110 and [3H]ryanodine binding to rabbit and frog skeletal muscle

AJP Cell Physiology ◽

10.1152/ajpcell.1994.266.2.c462 ◽

1994 ◽

Vol 266 (2) ◽

pp. C462-C466 ◽

Cited By ~ 42

Author(s):

K. Anderson ◽

A. H. Cohn ◽

G. Meissner

Keyword(s):

Skeletal Muscle ◽

Rabbit Skeletal Muscle ◽

Muscle Membrane ◽

Scatchard Analysis ◽

Physical Interaction ◽

Frog Skeletal Muscle ◽

Release Channel ◽

High Affinity ◽

Voltage Dependent ◽

Student’S T

In vertebrate skeletal muscle, the voltage-dependent mechanism of sarcoplasmic reticulum (SR) Ca2+ release, commonly referred to as excitation-contraction (E-C) coupling, is mediated by the voltage-sensing dihydropyridine receptor (DHPR), which is believed to affect SR Ca2+ release through a physical interaction with the SR ryanodine receptor (RYR)/Ca2+ release channel. Scatchard analysis of ligand binding of [3H]PN200-110 to the DHPR and [3H]ryanodine to the RYR indicated the presence of high-affinity sites in muscle homogenates, with maximum binding (Bmax) values of 72 +/- 26 and 76 +/- 30 pmol/g wet wt for rabbit skeletal muscle, and 27 +/- 14 and 44 +/- 13 pmol/g wet wt for frog skeletal muscle, respectively. The Bmax values corresponded to a PN200-110-to-ryanodine binding ratio of 0.98 +/- 0.26 and 0.61 +/- 0.24 for rabbit and frog skeletal muscle, respectively, and were found by Student's t test to be significantly different (P < 0.02, n = 7). These results are compared with measurements with isolated rabbit skeletal muscle membrane fractions and discussed in relation to our current understanding of the mechanism of E-C coupling in skeletal muscle.

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