Kinetic analysis of glutamate-induced chloride current in Aplysia neurones: a 'concentration clamp' study

L-Glutamate (Glu) applied by the 'concentration clamp' technique to isolated neurones of Aplysia induced a chloride current (ICl) by activating a single population of the channel. The concentration-response curve for the peak ICl gave a dissociation constant of 1.3 x 10(-4) M and a Hill coefficient of 1.8. The current-voltage relationship was linear in the voltage range examined (-60 to +10 mV). The activation phase of the ICl followed a single-exponential time course and desensitization was complete with a double-exponential time course. The time constants for activation and desensitization decreased with increasing concentrations of Glu but were voltage-independent. The process of recovery from desensitization was also double-exponential. The single-channel conductance estimated by ensemble noise analysis was 50 +/- 4.7 pS (n = 4). These results suggest that the Glu receptor-Cl channel complex in Aplysia neurones consists of a single population with two binding sites for the agonist.