On the functional relationship between 45Ca2+ release and prolactin secretion in cultured rat pituitary tumour (GH3) cells.
We have evaluated the role of cellular Ca2+ transport associated with stimulus-secretion coupling in prolactin (PRL) producing rat pituitary adenoma cells (GH3 cells). The action of different substances, known to modify PRL secretion, on release of 45Ca2+ from preloaded cells were examined. Surface-bound 45Ca2+ was removed by pretreatment with trypsin in EDTA buffer. During the first 6 min, basal efflux of 45Ca2+ occurred at a constant rate (0.24 min-1) at 37 degrees C. Addition of TRH (5 X 10(-7) M) resulted in an immediate enhancement of 45Ca2+ release representing about 20% of the remaining cellular 45Ca2+. In the same experiments PRL secretion increased by 45%. The EDTA in the external medium reduced the basal rate of 45Ca2+ release by 60%, but did not apparently affect the TRH-stimulated release. Somatostatin (10(-6) M) and verapamil (5 X 10(-5) M) inhibited both basal and TRH-stimulated PRL secretion, whereas high extracellular concentration of K+ (5 X 10(-2) M) had a stimulatory effect. However, neither of these treatments changed cellular 45Ca2+ release. Interference with energy-dependent Ca2+ transport by using metabolic inhibitors (iodoacetate, 6 X 10(-3) M; and antimycin, 2 X 10(-6) M) or by replacing Na+ in the medium by choline or by lowering the incubation temperature from 37 to 25 degrees C, had no effect on TRH-stimulated 45Ca2+ release although basal and TRH-stimulated PRL secretion were reduced. Thus, TRH apparently releases 45Ca2+ from calcium binding sites in the cell membrane.
Iversen
J G
JG
Sletholt
K
K
Haug
E
E
Gautvik
K M
KM
D000236:Adenoma / Q000378:metabolism*; D000818:Animals; D001971:Bromocriptine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D007700:Kinetics; D010911:Pituitary Neoplasms / Q000378:metabolism*; D011388:Prolactin / Q000378:metabolism*; D051381:Rats; D013004:Somatostatin / Q000494:pharmacology; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology
D001971:Bromocriptine; D013004:Somatostatin; D013973:Thyrotropin-Releasing Hormone; D011388:Prolactin; D002118:Calcium