Difference in calcium requirements for forskolin-induced release of prolactin from normal pituitary cells and GH4C1 cells in culture.
We investigated the role of Ca++ in cAMP-stimulated PRL release from 1) primary cultures of male rat pituitary glands, 2) primary cultures of estrogen-induced pituitary tumors from Fischer rats, and 3) the pituitary tumor cell line GH4C1. Forskolin, an activator of adenylate cyclase, increased intracellular cAMP concentrations in GH4C1 cells at least 20-fold within 15 min. This increase occurred in the presence or absence of added extracellular Ca++ or in the presence of D600 or Co++. Forskolin increased PRL release from the three types of cells. The three systems differed in the Ca++ sensitivity of forskolin-induced release, but showed little difference in the Ca++ sensitivity of K+-induced release. This was shown in two ways. The cells were incubated either 1) in a medium without added Ca++ or 2) in the presence of a Ca++ channel inhibitor, D600. In normal cells, K+- and forskolin-induced release were equally inhibited when extracellular Ca++ was removed or D600 was added. In GH4C1 cells, Ca++ removal or D600 addition (100 microM) completely blocked K+-induced release, but had little effect on forskolin-induced release. The response of Fischer tumor cells was intermediate between those of normal and GH4C1 cells. 45Ca++ uptake by GH4C1 cells was not affected by forskolin, whereas the release of 45Ca++ from preloaded cells was increased slightly only 30 min after the addition of forskolin in three of four experiments. The difference in Ca++ requirements between normal and GH4C1 cells for forskolin stimulation may be due to the release of cellular Ca++ stores by cAMP. These stores may not be as large in normal cells as they are in GH4C1 cells, and therefore the requirement for extracellular Ca++ occurs. Alternatively, GH4C1 cells may release PRL by a mechanism different from that which normal cells use.
D000818:Animals; D000959:Antihypertensive Agents / Q000494:pharmacology*; D002118:Calcium / Q000494:pharmacology*; D002460:Cell Line; D002478:Cells, Cultured; D005576:Colforsin; D000242:Cyclic AMP / Q000378:metabolism; D004224:Diterpenes / Q000494:pharmacology*; D005711:Gallopamil / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000378:metabolism*; D010911:Pituitary Neoplasms / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains
D000959:Antihypertensive Agents; D004224:Diterpenes; D005576:Colforsin; D005711:Gallopamil; D000242:Cyclic AMP; D011188:Potassium; D002118:Calcium