A GUANINE NUCLEOTIDE-BINDING PROTEIN MEDIATES THE INHIBITION OF VOLTAGE-DEPENDENT CALCIUM CURRENTS BY DOPAMINE IN RAT LACTOTROPHS

The present study examines the effect of dopamine (DA), known to inhibit prolactin (PRL) release, on voltage-actiaated calcium currents an identified rat lactotrophs. Two types of voltage-dependent Ca2+ currents were recorded using the whole-cell mode of the patch-clamp technique. Both reversibly inhibited by DA application. The inhibitory action of DA was reduced by (i) sulpiride (D2 antagonists), (ii) preincubation of the cells with pertussis toxin (PTX), and (iii) inclusion of guanosine 5′-O-(2-thiodiphosphate) (GDP-β-S) in the pipette solution, whereas it was potentiated by guanosine 5′-O-(3-thiotriphosphate) (GTP-γ-S). This DA-induced response could not be overcome by changing the adenosine 3′,5′-cyclic monophosphate level. These findings suggest that DA can inhibit Ca2+ entry through voltage-activated channels via a PTX-sensitive G protein(s) pathway thereby affecting PRL release from rat lactotrophs. © 1990.