Stimulatory effect of endothelin-1 on Na-dependent phosphate transport andits signaling mechanism in osteoblast-like cells

Endothelin-1 (ET-1) has been reported to modulate bone metabolism both in v ivo and in vitro. In the present study, we investigated the effect of ET-1 on inorganic phosphate (Pi) transport in osteoblast-like cells, which is no w considered to be important for the initiation of bone matrix calcificatio n. ET-1 time- and dose-dependently stimulated Na-dependent Pi transport in mouse calvaria-derived osteoblast-like MC3T3-E1 cells, and this effect was dependent on transcriptional and translational process. Kinetic analysis in dicated that the change in Pi transport activity induced by ET-1 was due to alteration in the number of the Pi transporter. BQ123, a selective antagon ist for ETA receptor, suppressed the ET-1-induced Pi transport, but BQ788, a selective antagonist for ETB receptor, had no effect. The inhibition of p hosphoinositide hydrolysis by phospholipase C (PLC) partially attenuated th e Pi transport by ET-1. Propranolol, which inhibits phosphatidic acid phosp hohydrolase, also suppressed ET-1-induced Pi transport. On the contrary, in domethacin did not affect the stimulatory effect of Pi transport by ET-1. C alphostin C, a protein kinase C (PKC) inhibitor, significantly blunted the stimulatory effect of ET-1 on Pi transport. Combined effect of PMA and ET-1 on Pi transport was not additive. Pi transport induced by ET-1 was also su ppressed in PKC down-regulated cells. In conclusion, the results of the pre sent study indicate that, in MC3T3-E1 osteoblast-like cells, ET-1 acting th rough ETA receptor links to a stimulation of Pi transport via activation of PKC through both phosphoinositide and phosphatidylcholine hydrolyses. J. C ell. Biochem. 83: 47-55, 2001. (C) 2001 Wiley-Liss, Inc.