Mechanisms of membrane estrogen receptor-α-mediated rapid stimulation of Ca2+ levels and prolactin release in a pituitary cell line

The role of membrane estrogen receptor-alpha (mERalpha) in rapid nongenomic responses to 17beta-estradiol (E-2) was tested in sublines of GH3/B6 rat prolactinoma cells selected for high (GH3/ B6/F10) and low (GH3/B6/D9) mERalpha expression. E-2 elicited rapid, concentration-dependent intracellular Ca2+ concentration ([Ca2+](i)) increases in the F10 subline. Lack of inhibition by thapsigargin depletion of intracellular Ca2+ pools, together with abrogation of the response in Ca2+-free medium, suggested an extracellular source of Ca2+ for this response. The participation of voltage-dependant channels in the E-2-induced [Ca2+](i) increase was confirmed by the specific L-type Ca2+ channel inhibitor nifedipine. For comparison, the D9 mERalpha-depleted subline was insensitive to steroid action via this signaling mechanism. [Ca2+](i) elevation was correlated with prolactin (PRL) release in the F10 cell line in as little as 3 min. E-2 caused a much higher PRL release than KCl treatment ( which caused maximal Ca2+ elevation), suggesting that secretion was also controlled by additional mechanisms. Participation of mERalpha in these effects was confirmed by the ability of E-2-peroxidase ( a cell-impermeable analog of E-2) to cause these responses, blockage of the responses with the ER antagonist ICI 182 780, and the inability of the E-2 stereoisomer 17alpha-E-2 to elicit a response. Thus rapid exocytosis of PRL is regulated in these cells by mERalpha signaling to specific Ca2+ channels utilizing extracellular Ca2+ sources and additional signaling mechanisms.