Endothelin-1 (ET-1) has been reported to modulate bone metabolism both in vivo 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 now considered to be important for the initiation of bone matrix calcification. 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 indicated 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 antagonist for ET(A) receptor, suppressed the ET-1-induced Pi transport, but BQ788, a selective antagonist for ET(B) receptor, had no effect. The inhibition of phosphoinositide hydrolysis by phospholipase C (PLC) partially attenuated the Pi transport by ET-1. Propranolol, which inhibits phosphatidic acid phosphohydrolase, also suppressed ET-1-induced Pi transport. On the contrary, indomethacin did not affect the stimulatory effect of Pi transport by ET-1. Calphostin 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 suppressed in PKC down-regulated cells. In conclusion, the results of the present study indicate that in MC3T3-E1 osteoblast-like cells, ET-1 acting through ET receptor links to a stimulation of Pi transport via activation of PKC through both phosphoinositide and phosphatidylcholine hydrolyses.
Copyright 2001 Wiley-Liss, Inc.