Membrane binding sites and non-genomic effects of estrogen in cultured human pre-osteoclastic cells

Besides functional estrogen receptors, the presence of signalling cell surface binding sites for 17 beta-estradiol (17 beta E(2)) has been reported in osteoblast- and osteoclast-like cells, suggesting that 17 beta E(2) may influence bone remodelling by a dual mechanism of action: to affect gene expression mediated by the nuclear activity of the steroid-receptor complex, and to initiate rapid responses triggered by a signal-generating receptor on the cell surface. Recently, we demonstrated that the human preosteoclastic cell line FLG 29.1 bears functional estrogen receptors. In this study we examined FLG 29.1 cells for the presence of cell surface binding sites for 17 beta E(2), and whether 17 beta E(2) could elicit cell signalling. Using a cell-impermeant and fluorescent estrogen conjugate, 17 beta-estradiol-6-carboxymethyloxime-bovine serum albumin-fluorescein isothiocyanate, we demonstrated the presence of specific plasma membrane binding sites for 17 beta E(2). Stimulation of FLG 29.1 cells with low (1 nM) and high (1 mu M) doses of 17 beta E(2) induced a prompt and significant (P < 0.05) increase of cellular pH, as measured in single cells using an image analysis system. In addition, both cAMP and cGMP were significantly increased by 17 beta E(2) with a dose-dependent response. Finally, a rapid increase of intracellular calcium ion concentration [Ca2+] was also induced by 1nM 17 beta E(2), as measured in single cells using an image analysis system. Our findings strongly suggest a non-genomic action of 17 beta E(2) on osteoclast precursors. Copyright (C) 1996 Elsevier Science Ltd.