Dibutyryl Cyclic AMP and Forskolin Inhibit Phosphatidylinositol Hydrolysis, Ca²⁺ Influx and Contraction in Vascular Smooth Muscle

Abstract

Dibutyryl cyclic AMP and forskolin inhibited the contraction induced by norepinephrine (NE) more strongly than the high K⁺-induced contraction in isolated rat aorta. These inhibitors inhibited the ⁴⁵Ca²⁺ influx stimulated by NE but not that by high K⁺, and they inhibited NE-induced inositol monophosphate accumulation. These results suggest that cAMP inhibits NE-induced contraction, at least partly, by inhibiting the α-adrenoceptor-mediated signal transduction and high K⁺-induced contraction by decreasing Ca²⁺ sensitivity but not Ca²⁺ influx.