A tremendous volume of work has been published on the opposing effects of potassium and calcium in various biological systems, including nervous tissue. The investigatiens on nerve have covered a number of its properties but have rarely includcd systematic study of the extent to which the effects of an excess of one cation can be offset by an excess of the opposing cation, or on the other hand can be duplicated by a deficit of the opposing cation. It therefore is uncertain whether the different properties of nerve are affected independently by the concentration of potassium ions and that of calcium ions, or by the ratio between these two concentrations. Obviously the effects of t~o kinds of ions might be antagonistic grossly even though they act characteristically on different parts of the nerve mechanism.The experiments on frog sciatic nerves reported here represent an investigation into the opposing actions of potassium and calcium on certain nerve functions known to be very sensitive to cations: the recovery process after stimulation in particular, the negative after-potential and incidentally the spike. When the experiments were begun it was thought that in addition to providing information cn the activity of potassium and calcium relative to each other, t h e y might serve to differentiate between otherwise hardly separable aspects of nerve behavior, ff some features proved to be controlled by the ratio between the two cationic concentrations, and others by the potassium or calcium concentration alone. In the group of functions selected for study, however, no classification according to form of cationic control and but slight differentiation proved to be possible.
MethodsSingle sciatic nerves isolated from green frogs (Rana pipiens) were immersed in "standard" Ringer's solution (NaC1 0.120 molar, KC1 0.0044 molar, CaCI~ 0.0032 molar) until mounted on recording and stimulating electrodes in air in a moist chamber, In an attempt to secure some constancy of condition in the nerve, the mounted nerve was left for some time with occasional stimulation (9) before the observations regarded as normal were begun. The time elapsed between isolation of the nerve and these observations was at least half an hour. Following these observations, the 493