Superoxide anions inhibit intracellular calcium response in porcine airway smooth muscle cells.

BACKGROUND: Superoxide anions (O2-) have multiple effects on pulmonary parenchyma altering cell proliferation, cellular metabolism, and airway smooth muscle (ASM) contraction. Intracellular Ca2+ concentration ([Ca2+]i) plays a significant role in the regulation of ASM contraction, relaxation, proliferation, and gene expression. OBJECTIVE: We investigated the effects of O2- on agonist-stimulated changes in [Ca2+]i in ASM cells. DESIGN/METHODS: Fura-2 AM-loaded, freshly isolated porcine ASM (PASM) cells were used to examine [Ca2+]i release in response to acetylcholine (ACh), histamine, endothelin, caffeine, and thapsigargin in the presence or absence of extracellular calcium. RESULTS: Exposure of PASM cells to xanthine and xanthine oxidase (X+XO) resulted in a time-dependent generation of O2-, inhibited by superoxide dismutase (SOD). Pre-incubating PASM cells with X+XO for 15- or 45-min inhibited net [Ca2+]i responses to ACh, Histamine, Caffeine, and Thapsigargin compared to control cells. Pretreating PASM cells with SOD for 30 min mitigated the inhibitory effect of X+XO treatment on ACh-induced Ca2+ elevation suggesting role of O2-. X+XO treatment also inhibited caffeine-and thapsigargin-induced Ca2+ elevation suggesting effect of O2- on intracellular calcium release and reuptake mechanisms. CONCLUSIONS: Superoxide attenuates [Ca2+]i release, reuptake and may interfere with physiological functions of ASM cells.