Activation of GabaA receptors increases [Ca2+]i in frog pituitary melanotropes

The neurotransmitter GABA regulates the activity of the pars intermedia in mammals and in submammalian vertebrates. In frog melanotrope cells, GABA acting through GABAA receptors causes a biphasic effect, that is, a rapid stimulation followed by a sustained inhibition of alpha MSH secretion. The present study investigates the intracellular events associated with the stimulatory phase of the response to GABA. Although our data demonstrate that, in frog pituitary melanotrophs, the stimulation of alpha-MSH secretion induced by GABA is coupled to a Cl- dependent influx of Ca2+ via nifedipine-sensitive channels.