Pulmonary artery smooth muscle cell [Ca2+](i) and contraction: responses to diphenyleneiodonium and hypoxia

To investigate mechanisms of inhibition of hypoxic pulmonary vasoconstriction (HPV), we studied pulmonary artery smooth muscle cell (PASMC) responses to hypoxia, utilizing diphenyleneiodonium (DPI), which blocks HPV. We measured cell contraction in primary cultures of rat PASMC grown on collagen gels and cytosolic free Ca2+ concentration ([Ca2+](i)) in PASMC grown on glass. DPI (5 and 20 mu M) caused contraction of PASMC and increased [Ca2+](i). Omission of extracellular Ca2+ diminished the DPI-induced PASMC contraction and greatly reduced the increase in [Ca2+](i). DPI substantially inhibited KCl-induced PASMC contraction (1 mu M DPI) and the increase in [Ca2+](i) (5 mu M DPI). Severe hypoxia contracted PASMC and quadrupled [Ca2+](i). DPI, 1 mu M, substantially inhibited hypoxic contraction, but neither 1 nor 5 mu M DPI diminished the hypoxia-induced increase in [Ca2+](i), which was greatly attenuated by 20 mu M DPI. These data show 1) that DPI increases [Ca2+](i), accounting for DPI-induced PASMC contraction and 2) that 1 and 5 mu M DPI inhibit the hypoxia-induced contraction but not the hypoxia-induced increase in [Ca2+](i), suggesting that DPI inhibits hypoxic PASMC contraction downstream of the Ca2+ signal by desensitizing the contractile apparatus and indicating a potential control point for modulation of HPV.