Ca²⁺-Dependent and Independent Mechanisms of Sustained Contraction in Vascular Smooth Muscle of Rat Aorta

Abstract

Norepinephrine (NE), prostaglandin F_2α (PG), 12-deoxyphorbol 13-isobutyrate (DPB) and high K⁺ induced sustained increase in cytosolic Ca²⁺ ([Ca²⁺]_i) and muscle tension in rat aorta. Verapamil, at the concentration which abolished the high K⁺-induced changes, also abolished the increase in [Ca²⁺]_i due to NE, PG and DPB although contractions were only partially inhibited. Excess EGTA further decreased [Ca²⁺]_i although a part of the contraction was not inhibited. These results indicate that the sustained contractions induced by NE, PG and DPB are due to increase in [Ca²⁺]_i, increase in Ca²⁺ sensitivity of contractile elements, and a Ca²⁺-independent mechanism.