Thyrotropin-releasing hormone stimulation of prolactin release from clonal rat pituitary cells: evidence for action independent of extracellular calcium.

Content Provider	Semantic Scholar
Author	Gershengorn, Marvin C. Hoffstein, Sylvia T. Rebecchi, Mario J. Geras, E. Rubin, Brian G.
Copyright Year	1981
Abstract	Thyrotropin-releasing hormone (TRH) stimulates prolactin release and (45)Ca(2+) efflux from GH(3) cells, a clonal strain of rat pituitary cells. Elevation of extracellular K(+) also induces prolactin release and increases (45)Ca(2+) efflux from these cells. In this report, we distinguish between TRH and high K(+) as secretagogues and show that TRH-induced release of prolactin and (45)Ca(2+) is independent of the extracellular Ca(2+) concentration, but the effect of high K(+) on prolactin release and (45)Ca(2+) efflux is dependent on the concentration of Ca(2+) in the medium. The increment in (45)Ca(2+) efflux induced by 50 mM K(+) during perifusion was reduced in a concentration-dependent manner by lowering extracellular Ca(2+) from 1,500 to 0.02 muM (by adding EGTA), whereas 1 muM TRH enhanced (45)Ca(2+) efflux similarly over the entire range of extracellular Ca(2+) concentrations. Although 50 mM K(+) caused release of 150 ng prolactin from 40 x 10(6) GH(3) cells exposed to 1,500 muM Ca(2+) (control), reduction of extracellular Ca(2+) to 2.8 muM decreased prolactin release caused by high K(+) to <3% of controls and no prolactin release was detected after exposure to 50 mM K(+) in medium with 0.02 muM free Ca(2+). In contrast, TRH caused release of 64 ng of prolactin from 40 x 10(6) GH(3) cells exposed to medium with 1,500 muM Ca(2+), and release caused by TRH was still 50 and 35% of control in medium with 2.8 and 0.02 muM Ca(2+), respectively. Furthermore, TRH transiently increased by 10-fold the fractional efflux of (45)Ca(2+) from GH(3) cells in static incubations with 1,500 or 3.5 muM Ca(2+), hereby confirming that the enhanced (45)Ca(2+) efflux caused by TRH in both low and high Ca(2+) medium was not an artifact of the perifusion system.Data obtained with chlortetracycline (CTC), a probe of membrane-bound Ca(2+), were concordant with those obtained by measuring (45)Ca(2+) efflux. Cellular fluorescence of CTC varied with the extracellular Ca(2+) concentration and the duration of incubation. TRH decreased the fluorescence of cell-associated CTC in a manner strongly suggesting stimulus-induced mobilization of Ca(2+), and this effect was still demonstrable in GH(3) cells incubated in 50 mM K(+). These data suggest that TRH acts to mobilize sequestered cell-associated Ca(2+) reflected as a (45)Ca(2+) efflux which is independent of the extracellular Ca(2+) concentration. Mobilization of sequestered Ca(2+) into the cytoplasm may elevate free intracellular Ca(2+) and serve to couple stimulation by TRH to secretion of prolactin.
File Format	PDF HTM / HTML
DOI	10.1172/JCI110216
PubMed reference number	6787084
Journal	Medline
Volume Number	67
Issue Number	6
Alternate Webpage(s)	https://dm5migu4zj3pb.cloudfront.net/manuscripts/110000/110216/cache/110216.1-20141229145633-covered-253bed37ca4c1ab43d105aefdf7b5536.pdf
Alternate Webpage(s)	https://doi.org/10.1172/JCI110216
Journal	The Journal of clinical investigation
Language	English
Access Restriction	Open
Content Type	Text
Resource Type	Article