维生素C对蟾蜍腓肠肌连续等长收缩期间松弛能力的影响

Effects of ascorbic acid on relaxation of ex vivo Bufo gastrocnemius during sustained isometric contraction

目的考察维生素C(VC)对离体蟾蜍腓肠肌连续等长收缩期间松弛能力的影响。方法药物处理30 min后,记录恒压电刺激蟾蜍腓肠肌等长收缩7.0 min内的张力变化,单指数函数加权拟合90%峰张力后的松弛过程,用对应松弛速度和静息张力表征松弛能力。结果抑制内源性抗氧化酶或用2.0 mmol/L VC单独处理对肌肉松弛能力影响很小。抑制超氧化物歧化酶(SOD)后VC可显著升高静息张力并大幅降低松弛速度,但抑制谷胱甘肽过氧化物酶和过氧化氢酶后VC效应很弱。同时抑制SOD、过氧化氢酶和谷胱甘肽过氧化物酶后,VC的效应同只抑制SOD相当。结论高浓度VC对富含过渡金属离子复合物而抗氧化能力低的生物体系有氧化毒性,此毒性可能涉及超氧阴离子介导的氧化损伤。

Objective To investigate the effect of ascorbic acid （VC） on relaxation of ex vivo Bufo gastrocnemius during sustained isometric contraction, Methods Dynamic tension of the muscle was recorded under constant voltage stimulation within 7.0 min at 2 s intervals. The rest tension and relaxation rate of the muscle was obtained by weighted fitting to the relaxation process of tension 〈90% of its peak with a mono-exponential model to characterize the muscular relaxation. Results VC at 2.0 mmol/L alone or in combination with the inhibitors of the antixoidation enzymes （surperoxide dismutase, glutathione peroxidase and catalase） resulted in negligible alterations in the muscular relaxation kinetics. VC combined with the inhibitor of surperoxide dismutase resulted in significantly lowered relaxation rate while increased rest tension, but VC with the inhibitor of either catalase or glutathione peroxidase showed negligible action. VC combined with the inhibitors of all the 3 enzymes also caused significant effect on the muscular relaxation kinetics, which was similar the effect of VC with superoxide dismutase inhibitor. Conclusion VC at high concentration may result in oxidative toxicity to the biological system rich in transitional metal ion complexes but with low antioxidation capacity by causing superoxide-mediated oxidative damages.