AIM　To study the effects of superoxide anion (O.2) on Ca2+ homeostasi and contractility in cultured bovine aortic smooth muscle cell. METHODS　Using Fura-2 fluorescence technique to determine Ca2+ level and collagen gel contraction system to analyze muscle contractility. RESULTS　ATP (10 μmol*L-1 )-induced Ca2+ transient was smaller in xanthine oxidase treated cells(X/XO) than control. The mean peak increment of ［Ca2+］i(△［Ca2+］i peak) and the time integral of the elevated ［Ca2+］i(∫△［Ca2+］i dt) for 5 min were decreased from (206.1±10.2) to (147.4±14.7) nmol·L-1,and from (12.2±0.5) to (9.8±0.8) μmol·L-1·s-1. Δ［Ca2+］i peak induced by thapsigargin（1 μmol·L-1 ）in Ca2+-free solution was not affected by X/XO, but was decreased from (27.3±1.0) nmol·L-1 to (13.5±1.0) nmol·L-1 in Ca2+-containing solution because of the activation of CRAC(△［Ca2+］i CRAC). X/XO accelerated the velocity of thapsigargin-induced Ca2+ leak from (78.7±3.4) s to (64.8±4.40) s. Gel contraction area in X/XO-treated cells induced by ATP or thapsigargin (in Ca2+ free solution and in Krebs solution)was decreased from 23.6%±4.6% to 7.4%±0.2%, from 3.5%±0.6% to -1.0%±0.5%, and from 7.9%±1.4% to -0.5%±0.7%, respectively. CONCLUTION　O.2 attenuats smooth muscle contraction by impairing some of Ca2+ mobilization pathways.

AIM To study the effects of superox- ide anion (O ) on Ca2+ homeostasi and contractility in cultured bovine aortic smooth muscle cell. METHODS Using Fura-2 fluorescence technique to determine Ca2+ level and collagen gel contraction system to analyze muscle contractility. RESULTS ATP (10 ?mol? L-1 )-induced Ca2+ transient was smaller in xanthine oxidase treated cells(X/XO) than control. The mean peak increment of [Ca2+ ]i (△[Ca2+ ], peak) and the time integral of the elevated [Ca2+ ], (∫ △[Ca2+ ]i dt) for 5 min were decreased from (206. 1 ? 10.2) to (147.4 ? 14.7) nmol? L-1, and from (12.2 ?0.5) to (9.8 ? 0.8) ?mol?L-1 .s-1. △ [Ca2+ ], peak induced by thapsigargin(1 ?mol. L- 1 ) in Ca2+ -free solution was not affected by X/XO, but was decreased from (27. 3 ? 1 .0) nmol? L－l to (13 .5 ? 1 .0 ) nmol? L- １ in Ca2+ -containing solution be cause of the activation of CRAC(△［Ｃa2+ ], CRAC). X/XO accelerated the velocity of thapsigargin-induced Ca2+ leak from (78.7 ? 3.4) s to (64.8 ? 4.40) s. Gel contraction area in X/XO-treated cells induced by ATP or thapsigargin (in Ca2+ free solution and in Krebs solution) was decreased from 23.6% ? 4.6% to 7.4% ?0.2%, from 3.5% ?0.6% to － l.0% ? 0.5%, and from 7.9% ? l.4% to － 0.5% ? 0.7%, respectively. CONCLUTION O2- attenuats smooth muscle contraction by impairing some of Ca2+ mobilization pathways.

SUMMARY AND PERSPECTIVE We demonstrated two kinds of impairing effect of glucose overload on endothelial Ca2+ mobilization; i.e., 02- mediated and protein kinase C-mediated ones. As already mentioned in the previous sections, endothelium-dependent vasodilation was impaired in aorta by the hyperglycemia-induced production of 02- (Tesfamariam & Cohen, 1992). In contrast, vasodilation in response to agonists such as acetylcholine and histamine was impaired by hyperglycemic condition in cerebral microvessels by the production of protein kinase C (Mayhan & Patel, 1995). Our observations happened to support these reports; i.e.,02-was responsible for glucose overload-induced impairment of Ca2+ mobilization in aortic endothelium and protein kinase C in brain microvascular endotheluim. However, because each mechanism affects Ca2+ mobilization in a quite different mauler, we suppose that this does not simply imply the site-specificity of the impairing action of glycose overload, but is due to the difference of Ca2+ mobilization mechanism. In other words,02- mainly affects Ca2+ pathways such as channels and pumps, and protein kinase C affects the signaling cascade which is related to Ca2+ mobilization. As summarized above, many Ca2+ mobilizing pathways, which are regulated by various biochemical and biomechanical stimulation, are involved in the regulation of endothelial [Ca2+]i. However, the details of such Ca2+mobilizing mechanism are not fully clarified. For instance, it is not known whether the cyclic AMP-mediated Ca2+ release observed in brain microvascular endothelium plays a significant role also in other vessels such as aortic endothelium. Therefore, the detailed clarification of the mechanisms of Ca2+ mobilization in vascular endothelium has an essential importance in vascular biology not only for physiological reason but also for pathophysiological reason.
Acetylcholine ; Aorta ; Biology ; Brain ; Calcium* ; Endothelial Cells* ; Endothelium ; Endothelium, Vascular ; Glucose* ; Histamine ; Homeostasis* ; Microvessels ; Protein Kinase C ; Protein Kinases ; Vasodilation