Endothelin- and sarafotoxin-induced receptor-mediated calcium mobilization in a clonal murine osteoblast-like cell...

Previous studies have demonstrated that, in osteoblast-like MC3T3-E1 cells, various endothelin peptides and their homologous sarafotoxins generate prostaglandin E(2) (PGE(2)) release through an ET(A) receptor subtype. In this study, biphasic Ca(2+) signals elicited with endothelin (ET)-1, ET-2, ET-3, beta-ET, S6a1, and S6b (ET/S6) were measured by microspectrofluorimetric methods in cell suspensions loaded with Fura-2 acetoxymethylester (Fura-2 AM). Phospholipase C (PLC)-dependent calcium activation mechanisms seem to be involved. We found evidence of Ca(2+) release from thapsigargin-sensitive and non-thapsigargin-sensitive intracellular Ca(2+) stores as well as Ca(2+) transmembrane inflow through multiple voltage-independent and Ni(2+)-sensitive cation channels. Using an ET(A) receptor antagonist, BQ-123, we showed that this receptor was coupled to Ca(2+) mobilization. All agonists tested, except S6c (an ET(B)-receptor-specific agonist) induced receptor desensitization. Our results demonstrate that the ET/S6-induced Ca(2+) signaling pathway is mediated via an ET(A)-receptor subtype in MC3T3-E1/B cells.