Potassium current and the effect of cesium on this current during anomalous rectification of the egg cell membrane of a starfish.

Abstract

The kinetics of the membrane current during the anomalous or inward-going rectification of the K current in the egg cell membrane of the starfish Mediaster aequalis were analyzed by voltage clamp. The rectification has instantaneous and time-dependent components. The time-dependent increase in K conductance for the negative voltage pulse as well as the decrease in the conductance for the positive pulse follows 1st-order kinetics. The steady-state conductance increases as membrane potential becomes more negative and reaches the saturation value at about -40 mV more negative than the K equilibrium potential, VK. The entire K conductance can be expressed by .hivin.gK .cntdot. n; .hivin.gK represents the component for the time-independent conductance which depends on V-VK and [K+]o, and n is a dimensionless number (1 .gtoreq. n .gtoreq. 0) and determined by 2 rate constants which depend only on V-VK. Cs+ does not carry any significant current through the K channel but blocks the channel at low concentration in the external medium. The blocking effect increases as the membrane potential is made more negative and the potential-dependent blocking by the external Cs+ also has instantaneous and time-dependent components.