Depression of peak force without altering calcium sensitivity by the superoxide anion in chemically skinned cardiac muscle of rat.

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Abstract
Among the mechanisms postulated to contribute to myocardial "stunning" is a depression of contractility by oxygen-derived free radicals. It has been suggested that these radicals might depress the calcium sensitivity of the contractile proteins. We have exposed the myofilaments (in chemically "skinned" rat cardiac muscle) to the superoxide anion and measured isometric force at controlled degrees of activation. Superoxide was generated by the xanthine/xanthine oxidase system: the effects to be described were shown to be specifically attributable to superoxide. Maximum calcium-activated force is reduced, or even completely abolished, in a dose-dependent fashion and without any alteration in calcium sensitivity. The myofilaments are highly sensitive to superoxide: significant force reduction has been shown to be caused by enzyme concentrations as low as 2 microunits/ml xanthine oxidase and with exposures of less than 1 minute to the generating system (at higher enzyme concentrations). Once force has been dep...