Mechanisms controlling vascular tone in pulmonary arterial hypertension: implications for vasodilator therapy

Pulmonary vasoconstriction is believed to be an early component of pulmonary arterial hypertension. Intracellular calcium concentration ([Ca(2+)](i)) is a major trigger for pulmonary vasoconstriction; however, it is now well known that contractions and relaxations may also be elicited through Ca(2+)-independent mechanisms. A variety of intracellular protein kinases and cyclic nucleotides have been identified as key determinants in controlling pulmonary vascular tone. Herein, we provide an overview of the main signaling pathways, which include protein kinase C, Rho kinases and cyclic nucleotides (cAMP and cGMP). This review also focuses on the role of store-operated Ca(2+) channels and voltage-gated K(+) channels, which are currently considered especially attractive in the pulmonary circulation and may represent new targets in the treatment of pulmonary arterial hypertension.