CA2-2 DOPAMINE-RECEPTORS( CURRENT EXPRESSION IN PITUITARY MELANOTROPHS OF NEONATAL RATS AND ITS REGULATION BY D)

1 We have examined the voltage-dependent Ca2+ channel activity of rat melanotrophs during the early postnatal period. The cells were dissoci ated from pituitary intermediate lobes, kept in culture for 5-24 h and then subjected to whole-cell patch-clamp experiments. 2. Like their a dult counterparts, neonatal melanotrophs were able to generate Na+ cur rents, K+ currents and Ca2+ currents in response to membrane depolariz ation. Ca2+ currents were carried by both low- and high-threshold Ca2 channels. 3. High-threshold Ca2+ current density decreased sharply be tween postnatal day 4 (P4) and P12. This period coincides with the ons et of dopaminergic innervation within the intermediate lobe. According ly, the developmental decrease in Ca2+ current density wax largely rev ersed by chronic in vivo treatment with sulpiride, a dopamine D-2 rece ptor antagonist. 4. Prolonging the time in culture from 5 h to 8 days did not significantly alter the Ca2+ channel activity of P3 melanotrop hs, whereas the high-threshold Ca2+ current in preciously innervated ( P14) melanotrophs stayed small for the first 24 h and then increased 3 -fold during the subsequent 4-5 days. This increase required RNA and p rotein synthesis and was prevented by adding D-2 agonists to the cultu re medium. 5. These results provide evidence for a postnatal suppressi on of high-threshold Ca2+ current expression in pituitary melanotrophs mediated by presynaptic dopamine neurons through D-2 dopamine recepto rs.