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 μM and W-7 (50 μM) inhibited PGE₂-induced increases in calcium uptake by OC cells, but had no effect on control OC or OB calcium levels. W-5 (50 μM), a chlorine-deficient analogue of W-7 with weak anti-calmodulin activity, had no effect. Compound 48 80 (100-500 μg/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 μg/ml) in both OC and OB cells but no effect on control levels. TFP at 50 μM inhibited both control and PGE₂-induced increases in cyclic AMP but at 10 μM it lessened only the hormone-induced effect. W-7 (100 μM) inhibited PGE₂-induced increases in OC and OB cyclic AMP but had no effect on control levels; W-5 (50 μM) 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. Lactic-acid production by OC or OB cells only decreased after 50 μM TFP, which suggests a specific, non-metabolic effect related to the other treatments.