EDN1 and pulmonary arterial hypertension: Despite the fact that overwhelming evidence suggests that alterations in pHi and Na+/H+ exchange are necessary for vascular smooth muscle cell growth, and that ET-1 levels are elevated pulmonary hypertension patients and animal models of pulmonary hypertension, the effect of ET-1 on basal pHi and NHE activity has yet to be examined in PASMCs.