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

A suppressant effect of intracelullar free Ca²⁺ on the γ-aminobutyric acid (GABA)-induced chloride inward current (I_Cl(GABA)) was studied in isolated frog sensory neurones under whole cell voltage clamp. Voltage-dependent Ca²⁺ influx elicited during the steady state of I_Cl(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 actions, 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.