Restoration of Membrane Excitability of Calcium-deficient Muscles by Anodal Polarization

Abstract

IT is well known that marked electrophysiological and biochemical disturbances occur in nerve and muscle immersed in calcium-free Ringer's solution¹. In the present experiment, isolated frog (Rana pipiens) sartorius muscles were used. When they were soaked in calcium-free Ringer solution (112 mM sodium chloride ; 2 mM potassium chloride ; 2.4 mM sodium bicarbonate), initial hyper-excitability was followed by a loss of excitability. This effect of calcium deficiency was enhanced by adding ethylene-diaminetetraacetic acid to the medium. In calcium-free Ringer containing 4 mM ethylenediaminetetra-acetic acid, muscles twitch while the resting potential rapidly drops to 50–30 mV. within an hour. As usual, the electrical activity which ordinarily accompanies stimulation was completely but reversibly eliminated in the 60–120 min. following immersion. This loss of excitability cannot be explained simply by the reduction of the resting potential, since a number of fibres showed, transiently, a relatively high resting potential in spite of a loss of excitability². Whether excitability was maintained depended on the susceptibility of individual fibres; even a seasonal variation being apparent. For example, the electrical activity of some muscles disappeared instantaneously in calcium-free Ringer, particularly in spring frogs. This seems to suggest that excitability depends on the properties of the membrane per se, which may be altered by the presence or absence of calcium ions.