Differences in kinetics between GABA(C) and GABA(A) receptors on carp retinal bipolar cells

The present work was undertaken to characterize kinetics, including activat ion, desensitization and deactivation, of responses mediated by GABA(A) and GABA(C) receptors on carp retinal bipolar cells, using the whole-cell patc h-clamp technique. It was revealed that the GABA(C) response was generally slower in kinetics than the GABA(A) response. Activation kinetics of both t he receptors could be well fit by monoexponential functions with time const ants tau, being 44.57 ms (GABA(C)) and 10.86 ms (GABA(A)) respectively. Des ensitization 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) respons e was fit by a monoexponential function of the time constant = 6.98 s. Deac tivation at both the receptors was adequately described by biexponential fu nctions 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) respo nse (tau (fast) = 42.07 ms; tau (slow) = 275.1 ms). These differences in ki netics suggest that GABA(C) and GABA(A) receptors may be involved in proces sing signals in different frequency domains.