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This Article Full Text Full Text (PDF) All Versions of this Article: 295/1/L104    most recent 00058.2008v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Lu, W. Articles by Sylvester, J. T. PubMed PubMed Citation Articles by Lu, W. Articles by Sylvester, J. T.

Differences in STIM1 and TRPC expression in proximal and distal pulmonary arterial smooth muscle are associated with differences in Ca²⁺ responses to hypoxia

Division of Pulmonary and Critical Care Medicine, Department of Medicine, The Johns Hopkins School of Medicine, Baltimore, Maryland

Submitted 3 February 2008 ; accepted in final form 16 April 2008

Hypoxic pulmonary vasoconstriction (HPV) requires Ca²⁺ influx through store-operated Ca²⁺ channels (SOCC) in pulmonary arterial smooth muscle cells (PASMC) and is greater in distal than proximal pulmonary arteries (PA). SOCC may be composed of canonical transient receptor potential (TRPC) proteins and activated by stromal interacting molecule 1 (STIM1). To assess the possibility that HPV is greater in distal PA because store-operated Ca²⁺ entry (SOCE) is greater in distal PASMC, we measured intracellular Ca²⁺ concentration ([Ca²⁺]_i) and SOCE in primary cultures of PASMC using fluorescent microscopy and the Ca²⁺-sensitive dye fura 2. Both hypoxia (4% O₂) and KCl (60 mM) increased [Ca²⁺]_i. Responses to hypoxia, but not KCl, were greater in distal cells. We measured SOCE in PASMC perfused with Ca²⁺-free solutions containing cyclopiazonic acid to deplete Ca²⁺ stores in sarcoplasmic reticulum and nifedipine to prevent Ca²⁺ entry through L-type voltage-operated Ca²⁺ channels. Under these conditions, the increase in [Ca²⁺]_i caused by restoration of extracellular Ca²⁺ and the decrease in fura 2 fluorescence caused by Mn²⁺ were greater in distal PASMC, indicating greater SOCE. Moreover, the increase in SOCE caused by hypoxia was also greater in distal cells. Real-time quantitative polymerase chain reaction analysis of PASMC and freshly isolated deendothelialized PA tissue demonstrated expression of STIM1 and five of seven known TRPC isoforms (TRPC1 > TRPC6 > TRPC4 >> TRPC3 TRPC5). For both protein, as measured by Western blotting, and mRNA, expression of STIM1, TRPC1, TRPC6, and TRPC4 was greater in distal than proximal PASMC and PA. These results provide further support for the importance of SOCE in HPV and suggest that HPV is greater in distal than proximal PA because greater numbers and activation of SOCC in distal PASMC generate bigger increases in [Ca²⁺]_i.

hypoxic pulmonary vasoconstriction; calcium signaling; vascular smooth muscle; potassium chloride; stromal interacting molecule 1; canonical transient receptor potential; calcium ion