THE RESTING MEMBRANE POTENTIAL AND CATION MOVEMENT IN FROG MUSCLE FIBERS AFTER EXPOSURE TO LITHIUM IONS

Abstract

1) The resting potential of sartorius muscle fibers of the frog was measured at room and cold temperature before and after exposure of the muscle to Li ions. Chemical analyses of muscles, which had been soaked in normal and Li Ringer's solution for varying periods, were carried out for Na, Li and K. 2) Immediately after replacement of normal Ringer's solution by Li Ringer's the muscle fiber showed a hyperpolarization of a few mV, which was followed by a gradual depolarization at room temperature, but at cold temperature the hyperpolarization was maintained for a long time. 3) The initial hyperpolarization is considered to result from the difference of the membrane permeability towards Li ions from Na, P_Li/P_Kbeing smaller (about 0.7) than P_Na/P_KThe delayed and gradual depolarization is attributed to a decrease in the active Na efflux resulting from a decrease in the internal Na concentration and from accumulation of Li inside the cell, which cannot extrude Li ions. 4) On re-immersion of the muscle, which had been soaked in Li Ringer's solution for 2 hr, in normal Ringer's solution at room temperature the muscle fiber was hyperpolarized. This is considered to result mainly from an increase in the active Na efflux, because at low temperature little hyperpolarization was seen. 5) The rates of Li influx and Na efflux, when muscles were immersed in Li Ringer's solution at normal and cold temperature, were calculated from the measurements on the ion content of the muscle. The rates of Li influx and Na efflux were found to be very fast during the initial 30 min after the immersion. They are several times faster than those reported previously. 6) The rates of Li efflux and Na influx were measured, when muscles, previously soaked in Li Ringer's solution for 2 hr, were re-immersed in normal Ringer's solution. The Li efflux rate was also fast during the initial 30 min after the re-immersion. It is smaller than the Na efflux rate, but of the similar order of magnitude. Thus it has been concluded that Li ions can cross the membrane passively at a rate comparable to that for Na.