Channel blocking drugs as tools to study glutamate receptors in insect muscles and molluscan neurons
The action of three dicationic drugs, derivatives of adamantane (IEM-1460 and IEM-1754) and phencyclidine (IEM-1925), on glutamate receptors (GluRs) at the insect neuromuscular junction (Calliphora vicina larva) and on neurons of the freshwater gastropodian molluscPlanorbarius corneus has been studied using the voltage clamp technique. In the presence of concanavalin A complex glutamate-induced currents recorded from molluscan neurons reflected mainly the opening of cationic channels as a result of decreased desensitisation and inhibition of a chloride component. Under these conditions all drugs studied inhibited the stationary component of glutamate-gated cationic currents in a dose-dependent manner (IC50s were 0.1 μM, 1.0 μM and 19.2 μM for the action of IEM-1925, IEM-1460 and IEM-1754 respectively). The same rank order of potency: IEM-1925 > IEM-1460 > IEM-1754 was observed in both the insect and mollusc. The results of these experiments are compared with those obtained earlier on vertebrate GluRs. Open-channel blocking drugs may help to identify and classify GluRs of invertebrates, and could be used as tools to elucidate the involvement of GluRs in the transmission at certain synapses.