Effects of superoxide anion on intracellular Ca2+ concentration in rabbit pulmonary arterial smooth muscle cells

AIM: To study the effect of superoxide anion on the Ca2+ homeostasis in smo oth muscle cells isolated from the rabbit pulmonary artery. METHODS: Intracellular Ca2+ concentration ([Ca2+](i)) was investigated usin g cell suspension of freshly isolated smooth muscle cells from rabbit pulmo nary artery (PASMC). Fura-2 fluorescent ratio obtained at 340 nm and 380 nm wave lengths was measured as an indicator of [Ca2+](i). RESULTS: ATP 30 mu mol.L-1 induced a transient increase in the ratio (Ca2transient). Thapsigargin, an inhibitor of sarcoplasmic Ca2+ ATPase, induced a phasic increase in the ratio due to Ca2+ leak from intracellular store s ites, but not the sustained increase, thereby suggesting the absence of Ca2 + release-activated Ca2+ entry (CRAC) mechanism in PASMC. When PASMC were e xposed to superoxide anion by the pretreatment with xanthine and xanthine o xidase (X/XO) for 30 min, sustained component of ATP-induced Ca2+ transient was elevated. The ratios at 5 and 10 min after ATP application (Delta rati o(5) (min) and Delta ratio(10) (min)) were increased from 0.091 +/- 0.022 t o 0.149 +/- 0.048 (P < 0.05) and from 0.021 +/- 0.020 to 0.117 +/- 0.047 (P < 0.01), respectively. But, thapsigargin-induced [Ca2+](i) transient was n ot affected by X/XO. CONCLUSION: Superoxide anion makes ATP-induced Ca2+ transient sluggish, and does not affect Ca2+ leak pathway in PASMC.