Hyperpolarization slowly activates a potassium current in locust skeletal muscle

Abstract

An inward current activated by hyperpolarization, I_K,H, was studied under voltage clamp in locust skeletal muscle. The dependence of its reversal potential on [K⁺]_o and its insensitivity to changes in [Na⁺]_o indicate that the underlying conductance is a K⁺ conductance. The instantaneous currentvoltage (I–V)-relationship exhibits outward rectification. Activation and deactivation take seconds and have complex time courses. At 10 mM [K⁺]_o activation seems to start at a voltage ≥ mV more positive than the resting potential (∼ −68 mV). Ba⁺⁺ blocks I_K,H strongly; so do Rb⁺ and Cs⁺, the latter in a voltage dependent manner. The slow inward current bears similarities to anomalous rectifiers as well as to mixed, hyperpolarization-activated K⁺/Na⁺ currents in other tissues.