EXPRESSION AND FUNCTIONAL-CHARACTERIZATION OF A MELATONIN-SENSITIVE RECEPTOR IN XENOPUS OOCYTES

Melatonin (MEL) plays a central role in the regulation of seasonal cyc les and in the control of circadian rhythms in mammals. Functional MEL -sensitive receptors were expressed in Xenopus laevis oocytes followin g injection of poly (A)(+) RNA from rat brain. Administration of 0.1-1 00 mu mol/l MEL to voltage-clamped oocytes (holding potential: -70 mV) elicited oscillatory inward currents (reversal potential: -24 mV) whi ch could be blocked by 9-anthracenecarboxylic acid and caffeine, After preincubation with pertussis toxin (PTX) the MEL response disappeared . The expressed MEL-sensitive receptor probably activates Ca2+-depende nt chloride currents via a PTX-sensitive G protein and the phosphoinos itol pathway.