Zn2+ differentially modulates kinetics of GABA(C) vs GABA(A) receptors in carp retinal bipolar cells.

GABA(C) and GABA(A) receptors co-exist in retinal bipolar cells. In the present study the effects of zinc on the kinetics of currents mediated by GABA(C) and GABA(A) receptors were investigated in isolated carp bipolar cells, using whole-cell patch-clamp technique. We observed for the first time that zinc exerted opposite effects on kinetics of the GABA(C) and GABA(A) responses: zinc significantly slowed down activation and desensitization of the GABA(C) response, but accelerated those of the GABA(A) response; zinc dramatically accelerated deactivation of the GABA(C) response, whereas it had no apparent effect on deactivation of the GABA(A) response. These results suggest that zinc may be functionally important in regulating retinal signal transmission.