Pharmacological profile of store-operated Ca2+ entry in intrapulmonary artery smooth muscle cells

Store-operated Ca2+ entry (SOCE) plays an important role in the contraction and proliferation of pulmonary artery smooth muscle cells (PASMCs). The aim of this study was to characterise the pharmacological properties of the SOCE pathway in freshly isolated PASMCs from rat lung and to determine whether this Ca2+ entry pathway is sensitive to nitric oxide donor drugs. Following depletion of Ca2+ from the sarcoplasmic reticulum, by treating cells with thapsigargin, re-addition of Ca2+ produced an increase in cytosolic fluo-4 fluorescence that was sustained for the period that extracellular Ca2+ was present. Thapsigargin also increased the rate of quench of fura-2 fluorescence, confirming that SOCE was activated. The SOCE pathway was not affected by nifedipine or verapamil; however, it was inhibited by the divalent cations Ni2+ (10 μM) and Cd2+ (10 μM) by 47 ± 5% and 49 ± 5% respectively. SOCE was also inhibited 42 ± 5% by 2-aminoethoxydiphenyl borate (2-APB; 75 μM) and 58 ± 4% by Gd3+ (10 μM), although La3+ (100 μM) had little effect. None of the NO donors examined, including sodium nitroprusside, glyceryl trinitrate, and 2-(N,N-diethylamino)-diazenolate-2-oxide had any effect on SOCE. Thus, the pulmonary vasorelaxation produced by NO does not involve direct inhibition of SOCE in PASMCs. Western blot and immunocytochemistry using antibodies directed against specific TRPC subunits detected the presence of TRPC1, 3, and 6 in pulmonary artery and the pharmacological profile of SOCE in PASMCs favours a role for TRPC1 in mediating the underlying channels that are activated by store depletion.