THE EFECT OF CHLORIDE ION ON THE RESTING POTENTIAL OF FROG'S MUSCLE FIBERS

Abstract

Although a number of experiments have been presented, the mechanism of maintaining potential difference across the resting membrane is still obscure. The author has attempted to clarify the property of the plasma membrane and the membrane potential, by studying the effect of chloride ion on the resting membrane potential of the muscle fiber.Since the description of the resting potential of the muscle by Matteucci or by du Bois Reymond, many studies have been offered, among which Bernstein's theory is most known (1). Bernstein (2) concluded that because there was a remarkable difference between the internal and the external potassium concentration of the muscle fiber, the resting potential was caused by the selective permeability of potassium to a membrane. He interpreted the nature of the resting potential by using Nernst's theory.The recent development of the microelectrode technique has made it possible to measure the resting potential directly by means of the intracellular recording of a single fiber. Hodgkin et al. (3) showed that the resting potential of a single giant nerve fiber could be determined by the concentration difference between the intracellular and extracellular potassium by using the microelectrode. The relationship between the extracellular potassium concentration and the membrane resting potential has been studied in the nerve and muscle fibers (4), (5), (6), (7). These investigations have shown that there is a linear relationship between the value of the resting potential and the logarithm of external potassium concentrations, although lower potassium concentrations deviate from such linear relation. In a giant nerve fiber of loligo, Hodgkin and Katz (8) showed that the measured resting potential coincided with the potential value obtained by use of Goldman's constant field theory (9).Boyle and Conway (10) have shown that the resting potential is related to the concentration difference between external and internal potassium or chloride ion, which are in a Donnan's equilibrium. Adrian (11) has shown that the membrane potential in sulfate-Ringer does not differ from that in normal Ringer when external potassium concentration is kept high. However, in a low external potassium concentration, the resting potential is reduced by substituting sucrose or sodium sulfate for sodium chloride (11), (7). This suggests that chloride ion contributes to the membrane potential in a low external potassium concentration.The purpose of this experiment was to investigate the effect of chloride ion on the resting potential in different external potassium concentrations, particularly in low concentrations. The effects of fluoride and bromide ions on the resting potential have also been studied to compare with those of chloride ion.