Melatonin modulates gamma-aminobutyric acid(A) receptor-mediated currents on isolated carp retinal neurons

Modulation by melatonin of gamma -aminobutyric acid(A) (GABA(A)) receptor-m ediated responses was studied in bipolar and amacrine-like cells acutely is olated from carp retina, using the whole-cell patch-clamp technique. Melato nin of 1 mM accelerated desensitization of the GABA(A) receptors at both bi polar and amacrine-like cells. In addition, 1 mM melatonin hardly changed t he GABA(A) receptor-mediated response amplitude of bipolar cells, while it increased or decreased that of amacrine-like cells, depending on the concen tration of GABA applied. These modulatory effects, which can not be blocked by luzindole, a melatonin receptor antagonist, may be due to the allosteri c action caused by melatonin bound to a site of the GABA(A) receptors. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.