Abstract
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.