Acute hypoxia increases intracellular [Ca ] in pulmonary arterial smooth muscle by enhancing capacitative Ca entry

Wang, Jian, Larissa A. Shimoda, Letitia Weigand, Wenqian Wang, Dejun Sun, and J. T. Sylvester. Acute hypoxia increases intracellular [Ca ] in pulmonary arterial smooth muscle by enhancing capacitative Ca entry. Am J Physiol Lung Cell Mol Physiol 288: L1059 –L1069, 2005. First published January 21, 2005; doi:10.1152/ajplung.00448.2004.—Hypoxic pulmonary vasoconstriction (HPV) requires influx of extracellular Ca in pulmonary arterial smooth muscle cells (PASMCs). To determine whether capacitative Ca entry (CCE) through store-operated Ca channels (SOCCs) contributes to this influx, we used fluorescent microscopy and the Ca -sensitive dye fura-2 to measure effects of 4% O2 on intracellular [Ca ] ([Ca ]i) and CCE in primary cultures of PASMCs from rat distal pulmonary arteries. In PASMCs perfused with Ca -free Krebs Ringer bicarbonate solution (KRBS) containing cyclopiazonic acid to deplete Ca stores in sarcoplasmic reticulum and nifedipine to prevent Ca entry through L-type voltage-operated Ca channels (VOCCs), hypoxia markedly enhanced both the increase in [Ca ]i caused by restoration of extracellular [Ca ] and the rate at which extracellular Mn quenched fura-2 fluorescence. These effects, as well as the increased [Ca ]i caused by hypoxia in PASMCs perfused with normal salt solutions, were blocked by the SOCC antagonists SKF-96365, NiCl2, and LaCl3 at concentrations that inhibited CCE 80% but did not alter [Ca ]i responses to 60 mM KCl. In contrast, the VOCC antagonist nifedipine inhibited [Ca ]i responses to hypoxia by only 50% at concentrations that completely blocked responses to KCl. The increased [Ca ]i caused by hypoxia was completely reversed by perfusion with Ca -free KRBS. LaCl3 increased basal [Ca ]i during normoxia, indicating effects other than inhibition of SOCCs. Our results suggest that acute hypoxia enhances CCE through SOCCs in distal PASMCs, leading to depolarization, secondary activation of VOCCs, and increased [Ca ]i. SOCCs and CCE may play important roles in HPV.