VOltage Clamp Studies on Insect Skeletal Muscle: I. The Inward Current

Abstract

Membrane currents in the muscle fibre of larval mealworm, Tenebrio molitor were investigated under voltage-clamp conditions. An initial inward current, a transient outward current and a delayed outward current were distinguished. Increasing external calcium concentration increased the size of the inward current and shifted the reversal potential in a positive direction. The inward current persisted in Na-free media and TTX-saline. However, the current was suppressed by 15 mM-cobalt ions. Therefore, it was concluded that the inward current was carried by calcium ions. Although the inward current was markedly reduced when external sodium was replaced with glucose, it was concluded that the contribution of Na ions to the current was small. Calcium conductance showed voltage and time dependence. The inactivation variable fell below unity with increasing strength of hyperpolarizing prepulses.