The effects of calmodulin antagonists on prostaglandin E2-induced responses in rat calvarial bone cells

Osteoclastic (OC) and osteoblastic (OB) cells were isolated by sequential collagenase digestions of new-born rat calvaria. Prostaglandin E2(PGE2) did not alter total calmodulin levels after a 5 or 60 min incubation. The calmodulin antagonists, trifluoperazine (TFP) at 10-50 microM and W-7 (50 microM) inhibited PGE2-induced increases in calcium uptake by OC cells, but had no effect on control OC or OB calcium levels. W-5 (50 microM), a chlorine-deficient analogue of W-7 with weak anti-calmodulin activity, had no effect. Compound 48/80 (100-500 micrograms/ml), a highly effective calmodulin antagonist in other systems, had no effect on PGE2-induced calcium levels or control calcium uptake. There was inhibition of PGE2-induced increases in cyclic AMP by compound 48/80 (100 micrograms/ml) in both OC and OB cells but no effect on control levels. TFP at 50 microM inhibited both control and PGE2-induced increases in cyclic AMP but at 10 microM it lessened only the hormone-induced effect. W-7 (100 microM) inhibited PGE2-induced increases in OC and OB cyclic AMP but had no effect on control levels; W-5 (50 microM) had no effect on either of these. Dibutyryl cyclic AMP had no effect on control calcium uptake, PGE2-induced increases or W-7 inhibition of the PGE-2 effect on calcium uptake. The calmodulin antagonists, at doses which had affected only PGE2-induced increases in calcium uptake and/or cyclic AMP production, had no effect on leucine uptake by OC or OB cells.(ABSTRACT TRUNCATED AT 250 WORDS)