The existence of distinct classes of prostaglandin E 2 receptors mediating adenylate cyclase and phospholipase C pathways in osteoblastic clone MC3T3-E1

Abstract

We have reported previously that PGE 2 evoked an increase in intracellular calcium level ([Ca 2+] i) in mouse osteoblastic cells (1). Here, we investigated the effects of PGE 1 and PGF 2α on cAMP production and [Ca 2+] i in comparison with those of PGE 2. In osteoblastic clone, MC3T3-E1 cells, PGE 1 stimulated cAMP production, but had no effect on [Ca 2+] i, whereas PGF 2α evoked only [Ca 2+] i increase. In contrast, PGE 2 not only stimulated cAMP production, but also increased [Ca 2+] i. From the Scatchard plot analysis of PGE 2 it was confirmed that there were two classes of PGE 2 binding sites (Kd value, 9.2 nM; binding site, 29 fmole/mg protein, and Kd value, 134 nM; binding site, 148 fmole/mg protein). As the increase in [Ca 2+] i was caused by PGF 2α and PGE 2, but not by PGE 1, we investigated the displacement of [ 3H]-PGF 2α binding. The displacement capacity of unlabeled PGE 2 was about 110 of that of PGF 2α, while that of PGE 1 was very low even at 500-fold excess. These data indicate the possibility that the dual action of PGE 2 is mediated by distinct receptor systems.