Non-random openings and concentration-dependent lifetimes of glutamate-gated channels in muscle membrane

Our preliminary results¹ with a single concentration (10 ^-4 M) of L-glutamate suggested that a glutamate receptor-gated channel (glutamate channel) in locust extrajunctional muscle membrane could suddenly change its kinetic properties and switch from a short to a long lifetime mode. These results were obtained from denervated muscle² pretreated with the lectin concanavalin A^3,4 (Con A) to block glutamate receptor desensitization. We have since extended our patch clamp studies of locust muscle to cover a range of glutamate concentrations and to include innervated muscle and muscle which has not been treated with Con A. These new studies show that the lifetime of the glutamate channel depends on the concentration of glutamate in the patch electrode, which we explain by a multi-binding site receptor model. This model, and our finding that channel openings occur non-randomly, also accounts for the apparent transitions in channel lifetime described in our earlier publication.