Ca2+ current expression in pituitary melanotrophs of neonatal rats and its regulation by D2 dopamine receptors.
1. We have examined the voltage-dependent Ca2+ channel activity of rat melanotrophs during the early postnatal period. The cells were dissociated from pituitary intermediate lobes, kept in culture for 5-24 h and then subjected to whole-cell patch-clamp experiments. 2. Like their adult counterparts, neonatal melanotrophs were able to generate Na+ currents, K+ currents and Ca2+ currents in response to membrane depolarization. Ca2+ currents were carried by both low- and high-threshold Ca2+ channels. 3. High-threshold Ca2+ current density decreased sharply between postnatal day 4 (P4) and P12. This period coincides with the onset of dopaminergic innervation within the intermediate lobe. Accordingly, the developmental decrease in Ca2+ current density was largely reversed by chronic in vivo treatment with sulpiride, a dopamine D2 receptor antagonist. 4. Prolonging the time in culture from 5 h to 8 days did not significantly alter the Ca2+ channel activity of P3 melanotrophs, whereas the high-threshold Ca2+ current in previously 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 protein synthesis and was prevented by adding D2 agonists to the culture medium. 5. These results provide evidence for a postnatal suppression of high-threshold Ca2+ current expression in pituitary melanotrophs mediated by presynaptic dopamine neurons through D2 dopamine receptors.
Gomora
J C
JC
Department of Physiology, Biophysics and Neuroscience, National Polytechnic Institute, Mexico City, Mexico.
Avila
G
G
Cota
G
G
D000818:Animals; D000831:Animals, Newborn; D001971:Bromocriptine / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D003513:Cycloheximide / Q000494:pharmacology; D018492:Dopamine Antagonists / Q000494:pharmacology; D004558:Electric Stimulation; D004594:Electrophysiology; D008544:Melanocytes / Q000187:drug effects / Q000378:metabolism; D018408:Patch-Clamp Techniques; D010902:Pituitary Gland / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D017448:Receptors, Dopamine D2 / Q000819:agonists / Q000378:metabolism*; D013469:Sulpiride / Q000494:pharmacology
D015220:Calcium Channels; D018492:Dopamine Antagonists; D017448:Receptors, Dopamine D2; D001971:Bromocriptine; D013469:Sulpiride; D003513:Cycloheximide