ETA RECEPTOR MEDIATES THE SIGNALING OF ENDOTHELIN-1 IN OSTEOBLAST-LIKE CELLS

We previously reported that endothelin-1 (ET-1) stimulates phosphatidy lcholine-hydrolyzing phospholipase D independently of phosphoinositide hydrolysis in osteoblast-like MC3T3-E1 cells, In the present study, w e investigated the characteristics of the receptors mediating ET-1-ind uced intracellular signaling pathway in MC3T3-E1 cells, Cyclo-D-Trp-D- Asp-Pro-D-Val-Leu (BQ123), a selective ETA receptor antagonist, signif icantly inhibited the ET-1-induced formation of inositol phosphates in a dose-dependent manner in the range between 22 nmol/L (IC50) and 2.2 mu mol/L (IC50 x 100). On the contrary, N-cis-2,6-dimethylpiperidinoc arbonyl-L-gamma MeLeu-D-Trp(COOMe)-D-Nle-ONa (BQ788), a selective ETB receptor antagonist, had no effect on the ET-1-induced formation of in ositol phosphates in the range between 1.2 nmol/L (IC50) and 120 nmol/ L (IC50 x 100), BQ123 significantly suppressed the ET-1-induced format ion of choline dose-dependently, however, BQ788 did not affect the cho line formation. BQ123 also inhibited the ET-1-induced release of arach idonic acid, but BQ788 had little effect, The results strongly suggest that ETA receptor mediates the three intracellular signaling pathways of ET-1: (1) phosphoinositide hydrolysis by phospholipase C; (2) phos phatidylcholine hydrolysis by phospholipase D; and (3) arachidonic aci d release in osteoblast-like cells. (C) 1997 by Elsevier Science Inc. All rights reserved.