GRF elevates cytosolic free calcium concentration in rat anterior pituitary cells.
The effect of human growth hormone-releasing factor (GRF) on intracellular free calcium concentration ([Ca2+]i) was examined in rat anterior pituitary cells. The [Ca2+]i was monitored directly by means of the intracellularly trapped fluorescent indicator, fura-2. GRF rapidly elevated [Ca2+]i, reaching a new plateau within approximately 30 s. The half-maximally effective concentration of GRF was approximately 130 pM. GRF produced a maximal increase in [Ca2+]i by approximately 120 nM. The GRF (2 nM)-induced elevation of [Ca2+]i was abolished by removal of extracellular calcium (Ca2+ omitted, 2 mM EGTA). The GRF (2 nM)-caused rise in [Ca2+]i was largely reduced in the presence of the calcium channel blockers Mg2+ (31.2 mM) or nifedipine (1 microM). An increase in [Ca2+]i by approximately 60 nM was elicited by the addition of prostaglandin E2 (1 microM), which can stimulate growth hormone secretion independent of GRF receptors. These data indicate that GRF elevates the [Ca2+]i, possibly in somatotrophs; this GRF-induced increase in [Ca2+]i may depend on an influx of extracellular Ca2+, largely through Mg2+- and nifedipine-sensitive calcium channels.
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000818:Animals; D001572:Benzofurans; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D015232:Dinoprostone; D004987:Ethers / Q000494:pharmacology; D005456:Fluorescent Dyes; D016257:Fura-2; D013007:Growth Hormone-Releasing Hormone / Q000494:pharmacology*; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism; D015759:Ionomycin; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D009543:Nifedipine / Q000494:pharmacology; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000378:metabolism*; D011458:Prostaglandins E / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D013050:Spectrometry, Fluorescence
D001572:Benzofurans; D004987:Ethers; D005456:Fluorescent Dyes; D007473:Ion Channels; D011458:Prostaglandins E; D015124:8-Bromo Cyclic Adenosine Monophosphate; D015759:Ionomycin; D013007:Growth Hormone-Releasing Hormone; D008274:Magnesium; D009543:Nifedipine; D015232:Dinoprostone; D002118:Calcium; D016257:Fura-2