Effect of intracellular pH on ferret pulmonary arterial smooth muscle cell calcium homeostasis and pressure

In this study, we investigated the role of Na+/H+ antiport in regulating cytosolic (intracellular) pH (pH(i)) in isolated and cultured ferret pulmonary arterial smooth muscle cells (PSMC). We also studied the effects of modulating pH(i) on the cytosolic (intracellular) calcium concentration ([Ca2+](i)) in the PSMC and on the pulmonary arterial pressure (Ppa) of isolated ferret lungs. pH(i) was modulated by the NH4Cl washout method. To eliminate the contribution of Cl-/HCO3- exchangers, the PSMC and isolated lungs were perfused in HCO3--free buffer. Blocking the Na+/H+ antiporter decreased baseline pH(i) and prevented the recovery from NH4Cl washout-induced intracellular acidosis. Intracellular alkalinization caused an initial transient increase in both [Ca2+](i) and Ppa that were dependent on extracellular Ca2+ entry. Maintaining cytosolic alkalinization caused another increase in Ppa that was not associated with an increase in [Ca2+](i). Intracellular acidosis also caused an increase in [Ca2+](i) and Ppa. The cytosolic acidosis-induced increase in [Ca2+](i) and Ppa were mediated by both extracellular Ca2+ influx and release of stored intracellular Ca2+. Cytosolic acidosis also appears to have a direct effect on the smooth muscle contractile elements. Both cytosolic alkalosis and acidosis increased vascular reactivity.