Injection of Alkaline Cations into Cat Spinal Motoneurones

Abstract

THE effects of electrophoretic injection of some cations into cat spinal motoneurones have already been reported¹. The injection of K⁺ displaces only the equilibrium potential of the inhibitory post-synaptic potential because of the increased intracellular chloride concentration which is caused by the inward movement of Cl⁻ ions during the flow of the potassium-injecting current. On the other hand, the effects of Na⁺ injections are characterized by changes in the resting-, spike-, and after-potentials and the inhibitory post-synaptic potential, which can be explained by the intracellular increase of Na⁺, the reciprocal decrease of K⁺, and the secondary increase of Cl⁻. The recovery of these potentials subsequent to a Na⁺ injection represents the time-course of the sodium extrusion from the motoneurones. According to a recent analysis, the increased intracellular sodium concentration decreases exponentially with a mean time constant of 91 sec; virtually full recovery being attained after about 6 min². Several other cations have now been injected into cat motoneurones, and this article will describe the effects of injections of Li⁺, Cs⁺, and Rb⁺ ions on the motoneurone potentials and the rates of their removal from the cells.