Ca2+-mediated suppression of the GABA-response through modulation of chloride channel gating in frog sensory neurones.

A suppressant effect of intracellular free Ca2+ on the gamma-aminobutyric acid (GABA)-induced chloride inward current (ICI(GABA)) was studied in isolated frog sensory neurones under whole cell voltage clamp. Voltage-dependent Ca2+ influx elicited during the steady state of ICI(GABA)-induced a fast, slowly recovering current relaxation in the outward direction, the amplitude of which was dependent on total Ca2+ influx. This suppressant effect showed specificity for different divalent cations, suggesting action at a specific intracellular effector. Single channel recording revealed a Ca2+-dependent decrease in the duration of the open time of the GABA-gated Cl- channel without change in single channel conductance.