Endothelin- and sarafotoxin-induced receptor-mediated calcium mobilization in a clonal murine osteoblast-like cell line, MC3T3-E1/B

Previous studies have demonstrated that, in osteoblast-like MC3T3-E1 cells, various endothelin peptides and their homologous sarafotoxins generate prostaglandin E2 (PGE2) release through an ETA receptor subtype. In this study, biphasic Ca2+ signals elicited with endothelin (ET)-1, ET-2, ET-3, β-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 Ca2+ release from thapsigargin-sensitive and non-thapsigargin-sensitive intracellular Ca2+ stores as well as Ca2+ transmembrane inflow through multiple voltage-independent and Ni2+-sensitive cation channels. Using an ETA receptor antagonist, BQ-123, we showed that this receptor was coupled to Ca2+ mobilization. All agonists tested, except S6c (an ETB-receptor-specific agonist) induced receptor desensitization. Our results demonstrate that the ET/S6-induced Ca2+ signaling pathway is mediated via an ETA-receptor subtype in MC3T3-E1/B cells.