Printed in Great Britain SHORT COMMUNICATIONS IONIC SELECTIVITY OF THE CALCIUM CHANNELS IN INSECT LARVAL MUSCLE FIBRES

It is well known that the action potentials of insect muscle fibres are generally Ca-dependent (Washio, 1972; and others). The calcium channels involved in these spikes have recently been shown to pass Na as well as Ca ions in the larvae of the beetle Tenebrio molitor (Yamamoto & Washio, 1979) and in the locust (Mathers & Thesleff, 1979). In this report we examine whether the Ca channels of Tenebrio can pass Li+, NH4+, guanidine, choline and TEA. Li+, NH4+ and guanidine have been shown to negotiate Na channels (Binstock & Lecar, 1969; Hille, 1971, 1972). Membrane potentials were recorded from the segmental muscle fibres of the larva of a beetle, Tenebrio molitor, in similar fashion to that described previously (Yamamoto & Washio, 1979). The standard saline had the following composition (mmol/1)