ENDOTHELINS INHIBIT THE MINERALIZATION OF OSTEOBLASTIC MC3T3-E1 CELLSTHROUGH THE A-TYPE ENDOTHELIN RECEPTOR

We examined the effects of various endothelins on the mineralization o f mouse clonal preosteoblastic MC3T3-E1 cells. MC3T3-E1 cells expresse d mRNAs for endothelin (ET)-1 and the A-type receptor for ET (ETA). A pharmacological study also demonstrated the predominant expression of the ETA receptor. Northern blotting analysis revealed that ETs decreas ed the expression of mRNA for osteocalcin, which is a marker protein f or the maturation of osteoblastic cells. ET-1 also decreased in the de position of calcium by MC3T3-E1 cells in a dose-dependent manner and i t had an inhibitory effect even at 10(-11) M. The rank order of potenc y of ETs was ET-1 = ET-2 > ET-3. Brief treatment with 10(-7) M ET-1 on days 6-8 alone suppressed mineralization. ET-1 enhanced the rate of p roduction of inositol 1,4,5-trisphosphate (IP3) in MC3T3-E1 cells, but it had no effect on the rate of production of cAMP. Taken together, o ur data indicate that ET-1 might inhibit the mineralization of osteobl astic cells via an interaction with the ETA receptor, with generation of IP3 as the intracellular signal.