Effects of calmodulin antagonist (W-7) on phorbol ester (PMA)-induced contractile response in isolated rat aorta.

The aim of this study was to investigate effects of calmodulin antagonist (W-7) on the contractile response of the rat aorta induced by activation of protein kinase C (PKC) by phorbol ester. Phorbol 12-myristate 13-acetate (PMA) produced biphasic contraction i.e., a sustained contraction (initial contraction) and 17.9 +/- 1.7 min later, this progressively developed contraction was changed to a delayed contraction superimposed on the initial contraction. The delayed contraction was completely inhibited by treatment with nicardipine. The onset of the delayed contraction was significantly delayed by treatment with W-7, whereas same concentration of W-7 showed a weak relaxant effect (10%) on the PMA-induced maximal contraction of aorta. Higher concentration of W-7 strongly inhibited PMA-induced sustained contraction. These results suggest that PMA-induced biphasic contractile response may be regulated by calmodulin.