Effects of internal potassium and sodium on the anomalous rectification of the starfish egg as examined by internal perfusion.

Abstract

The effects of alterations of the intracellular ionic composition on the properties of anomalous (or inward) rectification of the egg membrane of the starfish, M. aequalis, were studied using an intracellular perfusion technique combined with analysis of the membrane current with the voltage-clamp technique. The inward rectification of the K conductance depends only on the membrane potential, V, when the K equilibrium potential, VK, is altered by changing the internal K+ concentration at a fixed external K+ concentration, while it depends on V - VK when VK is altered by changing the external K+ at a fixed internal K+ concentration. The gating of the K channel of the inward rectification depends on V and the external K+ concentration. The conductance of the K channel at a given voltage is roughly proportional to the square root of [K+]i when the latter is altered at a fixed external K+ concentration. Since the conductance is proportional to the square root of [K+]o when this is altered at a fixed internal K+ concentration, this conductance is proportional to the geometrical mean of the external and internal K+ concentrations. Intracellular Na+ ions are necessary for the activation of inward rectification; the K conductance increases sharply with internal Na+ concentration, reaching saturation at 200 mM. A similar potentiating effect is found for Li+, although it is weaker. Rb+, Cs+ and organic cations e.g., arginine, do not have this effect.