Superoxide Anions Inhibit Intracellular Calcium Response in Porcine Airway Smooth Muscle Cells.

Background  Superoxide anions (O 2 - ) have multiple effects on pulmonary parenchyma altering cell proliferation, cellular metabolism, and airway smooth muscle (ASM) contraction. Intracellular calcium ([Ca 2+ ] i ) concentration plays a significant role in the regulation of ASM contraction, relaxation, proliferation, and gene expression. Objective  We investigated the effects of O 2 - on agonist-stimulated changes in [Ca 2+ ] i in ASM cells. Design/Methods  Fura-2 AM-loaded, freshly isolated porcine ASM (PASM) cells were used to examine [Ca 2+ ] i release in response to acetylcholine (ACh), histamine, endothelin, caffeine, and thapsigargin (TPG) in the presence or absence of extracellular Ca 2+ . Results  Exposure of PASM cells to xanthine and xanthine oxidase (X + XO) resulted in a time-dependent generation of O 2 - , inhibited by superoxide dismutase (SOD). Preincubating PASM cells with X + XO for 15- or 45-minute inhibited net [Ca 2+ ] i responses to ACh, histamine, caffeine, and TPG compared with control cells. Pretreating PASM cells with SOD for 30 minutes mitigated the inhibitory effect of X + XO treatment on ACh-induced Ca 2+ elevation suggesting role of O 2 - . X + XO treatment also inhibited caffeine- and TPG-induced Ca 2+ elevation suggesting effect of O 2 - on [Ca 2+ ] i release and reuptake mechanisms. Conclusion  Superoxide attenuates [Ca 2+ ] i release, reuptake, and may interfere with physiological functions of ASM cells.