Effects of acute hypoxia on calcium signal of sarcoplasmic reticulum in pulmonary artery smooth muscle in rats

AIM:To investigate the effects of acute hypoxia on calcium of sarcoplasmic reticulum in pulmonary artery smooth muscle in rats.METHODS:The fluorescence Ca2+ indicator Fura-2/AM was used to observe intracellular free Ca2+ concentration([Ca2+]i)in rat pulmonary artery smooth muscle cells(PASMCs)in the presence of ryanodine(RD)and cyclopiazonic acid(CPA)in normal(37 ℃,5%CO2,21%O2,74%N2),acute hypoxic(37 ℃,5%CO2,2%O2,93%N2)under Ca2+ and Ca2+ free conditions.Pulmonary artery ring was used to determine the pulmonary artery tension by using routine blood vascular perfusion in vitro under the same conditions.RESULTS:(1)Under acute hypoxic conditions,[Ca2+]i was increased [(96.99±7.16)nmol/L in normoxic condition and(257.06±32.48)nmol/L in hypoxic condition,P0.01].(2)Ryanodine or procain,an agent that blocks ryanodine receptor-seneitive(RyR)Ca2+ stores,inhibited hypoxia-induced increases in [Ca2+]i { [Ca2+]i decreased to(100.91±11.21)nmol/L,P0.01}.CPA or thapsigargin(TG),the agent that inhibits sarcoplasmic reticulum(SR)Ca2+-ATPase and inhibits SR uptake Ca2+,increased [Ca2+]i.Under acute hypoxic and Ca2+ conditions,CPA or thapsigargin(TG)increased [Ca2+]i more than that in Ca2+ free conditions.(3)Acute hypoxia evoked pulmonary artery contractions.Pulmonary artery tension had no effects under normoxic and increased under acute hypoxia condition.(4)Ryanodine or procain inhibited hypoxia-evoked contractions in the pulmonary artery.CPA or TG increased artery tension.Under acute hypoxic and Ca2+ conditions,CPA or TG increased tension more than that in Ca2+ free condition.CONCLUSION:The results indicate that release of Ca2+ from the SR,at least,RyR Ca2+ store,contributes to the mechanism of hypoxic pulmonary vasoconstriction in rat.This is a mechanism intrinsic to pulmonary artery without the need for Ca2+ influx across the plasmalemma or an endothelial factor.