G alpha(q/11) and G beta gamma proteins and membrane signaling of calcitriol and estradiol

17 beta-estradiol and 1,25-dihydroxyvitamin D-3 (calcitriol) rapidly increa se (< 5 sec) the concentration of intracellular calcium by mobilizing Ca2from the endoplasmic reticulum and farming inositol 1, ct,5-trisphosphate ( InsP(3)) and diacylglycerol. Calcitriol increases InsP(3) formation via act ivation of phospholipase C (PLC)-beta 1 linked to a pertussis toxin (PTX)-i nsensitive C-protein, and estradiol via activation of PLC-beta 2 linked to a PTX-sensitive C-protein. Since PLC are effecters of different subunits of various C-proteins, we looked for and identified several G-subunits (G alp ha(q/11), G alpha s, G alpha i, G beta and G gamma) in female rat osteoblas ts using Western immunoblotting. The action of calcitriol on InsP(3) format ion and Ca2+ mobilization in Fura-2-loaded confluent osteoblasts involved G alpha(q/11). The membrane effects of estradiol involved G beta gamma; subu nits, and principally G beta subunits, but not alpha-subunits. These result s may provide additional evidence for membrane receptors of steroid hormone s. Since PLC-beta 1 is the target effector of G alpha(q/11), whereas PLC-be ta 2 is only activated by beta gamma subunits, this specificity may help to generate membrane receptor-specific responses in vivo. (C) 1999 Wiley-Liss , Inc.