Differences in kinetics between GABAC and GABAA receptors on carp retinal bipolar cells

The present work was undertaken to characterize kinetics, including activation, desensitization and deactivation, of responses mediated by GABA(A) and GABA(C) receptors on carp retinal bipolar cells, using the whole-cell patch-clamp technique. It was revealed that the GABA(C) response was generally slower in kinetics than the GABA(A) response. Activation kinetics of both the receptors could be well fit by monoexponential functions with time constants tau, being 44.57 ms (GABA(C)) and 10.86 ms (GABA(A)) respectively. Desensitization of the GABA(A) response was characterized by a fast and a slow exponential component with time constants of tau (fast) = 2.16 s and tau (slow) = 19.78 s respectively whereas desensitization of the GABA(C) response was fit by a monoexponential function of the time constant = 6.98 s. Deactivation at both the receptors was adequately described by biexponential functions with time constants being much higher for the GABA(C) response (tau (fast) = 674.8 ms; tau (slow) = 2 090 ms) than those for the GABA(A) response (tau (fast) = 42.07 ms; tau (slow) = 275.1 ms). These differences in kinetics suggest that GABA(C) and GABA(A) receptors may be involved in processing signals in different frequency domains.