Dopamine inhibits cell swelling-induced prolactin secretion in MMQ cells by blocking Ca2+ influx.
To evaluate the role of Ca2+ influx on hormone secretion induced by cell swelling, we have utilized a prolactin (PRL)-secreting rat tumor cell line, MMQ, which has plasmalemma dopamine receptors. Medium hyposmolarity or osmotically equivalent isotonic urea caused prompt cell swelling and a rise in both [Ca2+]i and PRL secretion in a dose-dependent manner. Dopamine inhibited the induced increase in both [Ca2+]i and PRL secretion in a dose-dependent manner but the maximum inhibition was only 50%. This effect of dopamine was prevented by haloperidol. Depletion of medium Ca2+ or blocking Ca2+ influx with nifedipine completely abolished the osmotically induced rise in both [Ca2+]i and PRL secretion. These data indicate that Ca2+ influx through nifedipine-sensitive Ca2+ channels is an essential component of PRL secretion induced by osmotic cell swelling in MMQ cells and that a dopaminergic receptor-linked mechanism influences the opening of these channels.
Sato
N
N
Department of Medicine, Oregon Health Sciences University, Portland 97201.
Wang
X B
XB
Greer
M A
MA
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D004298:Dopamine / Q000494:pharmacology*; D009994:Osmolar Concentration; D010902:Pituitary Gland / Q000166:cytology / Q000378:metabolism; D011388:Prolactin / Q000378:metabolism*; D051381:Rats; D014407:Tumor Cells, Cultured
D015220:Calcium Channels; D011388:Prolactin; D002118:Calcium; D004298:Dopamine