title: Susceptibility of caffeine- and Ins(1,4,5)P3-induced contractions to oxidants in permeabilized vascular smooth muscle.
abstract: Two principal pathways of Ca2+ release from the sarcoplasmic reticulum of excitable and non-excitable cells have been described: one pathway dependent on the second messenger D-myo-inositol 1,4,5-trisphosphate (Ins(1,4,5)P3), and a second pathway sensitive to Ca2+ and regulated by caffeine and ryanodine. It was found that the Ca(2+)-pump activity of vascular smooth muscle sarcoplasmic reticulum is inhibited by superoxide anion radicals (O2.-); however, the effects of reactive oxygen intermediates on sarcoplasmic reticulum Ca2+ release in vascular muscle cells are not well defined. The purpose of the present study was to evaluate the effects of reactive oxygen intermediates generated from the hypoxanthine/xanthine oxidase reaction system on contractions induced by caffeine, Ins(1,4,5)P3 and norepinephrine in staphylococcal alpha-toxin-permeabilized rabbit mesenteric arteries. This system generates O2.-, H2O2, and hydroxyl radicals. We wished to identify which class of reactive oxygen intermediates is responsible for the associated loss of vascular smooth muscle contractile function. Caffeine and Ins(1,4,5)P3 produced a transient contraction when the sarcoplasmic reticulum of the permeabilized, preparations was preloaded with pCa 7.0 solution for 5 min before washing with 0.5 mM EGTA solution; norepinephrine also produced a transient contraction. Exposure of the preparations to hypoxanthine/xanthine oxidase (for 30 min) attenuated caffeine-induced contraction, but was without effect on Ins(1,4,5)P3-induced contraction. The observed effect of hypoxanthine/xanthine oxidase exposure was superoxide dismutase-inhibitable, suggesting O2.- involvement. Hypoxanthine/xanthine oxidase also inhibited norepinephrine-induced contraction. The effect of hypoxanthine/xanthine oxidase on norepinephrine contraction was protected by catalase, but not by superoxide dismutase and dimethyl sulfoxide; exogenously added H2O2 mimicked the effect of hypoxanthine/xanthine oxidase exposure. H2O2, added exogenously, was without effect on Ins(1,4,5)P3-induced contraction. It is suggested that the pathway of Ca2+ release from the sarcoplasmic reticulum dependent on Ins(1,4,5)P3 is insensitive to O2.-. Instead, caffeine-induced Ca2+ release mechanisms may be susceptible to O2.- and H2O2, rather than O2.- and hydroxyl radicals, may be the active agent in the norepinephrine-induced contraction. Our results are also consistent with the view that the attenuation by H2O2 of the norepinephrine-induced contraction may be linked to the receptor-associated pathway of Ins(1,4,5)P3 formation, but not to degradation processes of Ins(1,4,5)P3.
authors.affiliation: Department of Pharmacology, Kanagawa Dental College, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Wada
authors.forename: E
authors.initials: E
authors.lastname: Okabe
mesh_terms: D000818:Animals; D002110:Caffeine / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000378:metabolism / Q000494:pharmacology; D017665:Hydroxyl Radical / Q000378:metabolism; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology*; D008297:Male; D008638:Mesenteric Arteries / Q000187:drug effects* / Q000502:physiology; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000502:physiology; D009638:Norepinephrine / Q000494:pharmacology; D010539:Permeability; D011817:Rabbits; D017382:Reactive Oxygen Species / Q000378:metabolism*; D013481:Superoxides / Q000378:metabolism; D010738:Type C Phospholipases / Q000494:pharmacology; D014662:Vasoconstrictor Agents / Q000494:pharmacology
chemical_list: D017382:Reactive Oxygen Species; D014662:Vasoconstrictor Agents; D013481:Superoxides; D017665:Hydroxyl Radical; D002110:Caffeine; D015544:Inositol 1,4,5-Trisphosphate; D006861:Hydrogen Peroxide; D010738:Type C Phospholipases; D002118:Calcium; D009638:Norepinephrine