The action of potassium and other ions on the injury potential and action current in maia nerve

Abstract

Analyses of Maia squinado blood serum and nerve show a K concn. per 100 gm. of water at least 13 times as great in the nerve as in the serum. The observed injury potential of Maia nerve was about 30 millivolts; at 17[degree]C a [plus or minus]5% reproducibility persisted for about 2 hrs., precautions being taken to eliminate the "crush sealing over" effect (Gerard, 1930). Solns. rich in KCl depressed both the injury potential and the action current rapidly and reversibly. The K concn. required to abolish the action current was about 5 times that in Maia serum; the depression of the action current could be partly prevented by the addition of an equimolecular concn. of CaCl2. Probably the reversible inexcitability which occurs in freshly dissected Maia nerves is due to an abnormal concn. of K ions at the external surfaces of the fibers; the K ions may have escaped either from the nerve or from the surrounding muscle fibers, as a result of small unavoidable injuries during the dissecfion. Rubidium and Cs ions also produced a reversible abolition of the action current, but 2.0 Rb or 3.2 Cs ions were required to give the effect of one K ion: the depressing action of these ions could be partly prevented by Ca ions. Nerves which had been immersed in K rich solns. gave an approximately linear relation between the logarithm of the KC1 concn. and the depression of the injury potential, although higher concns. than expected from the chemical analyses were required to make the potential zero. Probably the discrepancy is mainly due to the difficulty of isolating nerves uncontaminated by connective tissue and sea water, but other factors, such as the Donnan effect, may also operate. Resting nerves in sea water leaked little K salt, but nerves stimulated to fatigue leaked considerable amounts. Assuming that the long-continued recovery heat production of these nerves is due to a "secretory" process whereby ions are restored to their original positions, the thermodynamical efficiency is calculated to be 0.02. Severe asphyxia could produce a reversible in-excitability only to be removed by washing the nerve; it is suggested that K salts had escaped from the interior of the fibers.