Superoxide anion impairs contractility in cultured aortic smooth muscle cells

We examined the effects of superoxide anion (O-2(-)) generated by xanthine plus xanthine oxidase (X/XO) on the intracellular Ca2+ concentration ([Ca2+](i)) and muscle contractility in cultured bovine aortic smooth muscle cells (BASMC). Cells were grown on collagen-coated dish for the measurement of [Ca2+](i). Pretreatment with X/XO inhibited ATP-induced Ca2+ transient and Ca2+ release-activated Ca2+ entry (CRAC) after thapsigargin-induced store depletion, both of which were reversed by superoxide dismutase (SOD). In contrast, Ca2+ transients induced by high-K+ solution and Ca2+ ionophore A-23187 were not affected by X/XO. BASMC-embedded collagen gel lattice, which was pretreated with xanthine alone, showed contraction in response to ATP, thapsigargin, high-K+ solution, and A-23187. Pretreatment of the gel with X/XO impaired gel contraction not only by ATP and thapsigargin, but also by high-K+ solution and A-23187. The X/XO-treated gel showed normal contraction; however, when SOD was present during the pretreatment period. These results indicate that O-2(-) attenuates smooth muscle contraction by impairing CRAC, ATP-induced Ca2+ transient, and Ca2+ sensitivity in BASMC.