Glutamatergic channels in locust muscle show a wide time range of desensitization and resensitization characteristics

Outside-out patches of membrane were excised from locust muscle. 10 mM L-glutamate applied to such patches in short pulses elicited rapidly a peak of channel opening, followed by desensitization with time constants between 1 ms and 20 ms for different channel subtypes. Slowly rising glutamate concentrations could produce almost complete desensitization without any channel openings. Desensitization thus proceeds from a closed channel state, prior to channel opening. Resensitization, i.e. recovery from desensitization, was tested by applying pairs of glutamate pulses, varying the pulse interval. Resensitization has a biphasic time course. While in rapidly desensitizing channels more than 50% of resensitization was achieved within a few milliseconds, in slowly desensitizing channels resensitization took seconds.