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

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