The Capacitance of Skeletal Muscle Fibers in Solutions of Low Ionic Strength

Abstract

The capacitance of skeletal muscle fibers was measured by recording with one microelectrode the voltage produced by a rectangular pulse of current applied with another microelectrode. The ionic strength of the bathing solution was varied by isosmotic replacement of NaCl with sucrose, the [K] [C1] product being held constant. The capacitance decreased with decreasing ionic strength, reaching a value of some 2 F/cm 2 in solutions of 30 mM ionic strength, and not decreasing further in solutions of 15 mM ionic strength. The capacitance of glycerol-treated fibers did not change with ionic strength and was also some 2 uF/cm 2 . It seems likely that lowering the ionic strength reduces the capacitance of the tubular system (defined as the charge stored in the tubular system), and that the 2 ptF/cm 2 which is insensitive to ionic strength is associated with the surface membrane. The tubular system is open to the external solution in low ionic strength solutions since peroxidase is able to diffuse into the lumen of the tubules. Twitches and action potentials were also recorded from fibers in low ionic strength solutions, even though the capacitance of the tubular system was very small in these solutions. This finding can be explained if there is an action potential-like mechanism in the tubular membrane.

Inward movement of sodium ions in resting and stimulated frog's sartorius muscle

“…3 practically no twitch tension could be detected at external Na+ concentrations below 40 mm, at least for the experimental conditions used here. This result is at variance with those of Overton (1902), Edwards, Ritchie & Wilkie (1956), Mashima & Matsumura (1962), Grabowski, Lobsiger & Littgau (1972), and Vaughan, Howell & Eisenberg (1972), whose experiments indicate that at [Na+]. = 40 ml the twitch tension is still practically normal.…”

Electrical properties of toad sartorius muscle fibres in summer and winter

“…As mentioned above, Tamasige (1950) found a membrane resistance of 10,000 2. cm2. Vaughan, Howell & Eisenberg (1972) …”

Membrane capacity measurements on frog skeletal muscle in media of low ion content. With an Appendix

“…Vaughan et al (1972) have reported large drops in Cm when ionic strength of Ringer fluid is lowered by replacing NaCl isosmotically with sucrose. Their work was carried out with a constantcurrent technique, and it seemed ofinterest to repeat some oftheir measurements with the present method.…”

“…Membrane constants of eight fibres were also measured in a lowconductivity Ringer fluid (solution K in Table 1) identical in composition to '0-24 IS Ringer' of Vaughan et al (1972). Mean values + S.E.…”

“…As a result of this complication, the analysis of voltage transients in terms of the leaky-capacitator model can give rise to misleading results, especially if the series resistance is large, as one might expect it to be in solutions of low conductivity. Adrian & Almers (1973) have shown how this kind of uncertainty could have affected the results of Vaughan et al (1972).…”