Calcium Channel Currents In Neurones From Locust ( Schistocerca Gregaria ) Thoracic Ganglia

Abstract

Using the patch-clamp technique, Ca2+ channel currents were recorded from neurones freshly isolated from the thoracic ganglia of the desert locust Schistocerca gregaria. In solutions containing 10mmol l−1Ba2+ we observed high-voltage-activated whole-cell inward currents with sustained and transient components, both of which had similar steady-state inactivation properties. Substitution of Ca2+ for Ba2+ was found to reduce whole-cell currents, whereas removal of monovalent cations had no effect. Cd2+ (1mmol l−1) completely blocked the whole-cell current, but at 10 μmol l−1 preferentially inhibited the sustained component without affecting the transient component. Verapamil (1 μmol l−1) inhibited both current components but appeared to be more selective for the sustained component, whereas nitrendipine (1 μmol l−1) had no effect on either component. A single-channel recording suggested that the transient component was carried by a low-conductance channel. Certain compounds with insecticidal action (ryanodine, S-bioallethrin, deltamethrin and avermectin) did not affect calcium channel currents in these cells. These data suggest that there are two types of Ca2+ channels present in locust neurones. These channel types have properties differing from the T-, L- and N-type channels found in vertebrates and, furthermore, were not targets for the insecticides we tested.