Osmotic properties of frog nerve

Abstract

1. 1. Sciatic nerves of Rana pipiens were immersed in anisotonic Ringer solutions, 1 1 2 %–400% , and weight changes followed with a torsion balance. After attainment of equilibrium, reversibility in normal Ringer was determined. In 30% Ringer at 24°C, swelling equilibrium was attained in about 18 min. In very dilute solutions, equilibrium was reached at much longer times. 2. 2. The equilibrium volume appeared to follow Boyle's law, P( V − b) = k, up to dilutions as high as 15% Ringer; beyond that significant deviation was observed. 3. 3. The osmotically inactive fraction b = 86 per cent, in Ringer 50% and above; in more dilute solutions b increased progressively with the degree of hypotonicity. It is of greater magnitude in frog nerve than in other cells, such as marine eggs. 4. 4. Participation of the axones in the swelling was observed by microscopic measurement. In dilute solutions, changes in myelin sheath configuration were observed microscopically during swelling. 5. 5. Slowing of conduction velocity and lenghtening of absolute refractoriness were observed in both hyper- and hypotonic Ringer solutions, and, within limits, good reversal of electrical and weight changes were obtained in normal Ringer. 6. 6. The interpretation is advances that the observed electrophysiological changes in anisotonic solutions are attributable to altered axonal membrane ion permeability.