Superoxide, hydroxyl radical, and hydrogen peroxide effects on single-diaphragm fiber contractile apparatus

Reactive oxygen species contribute to diaphragm dysfunction in certain path ophysiological conditions (i.e., sepsis and fatigue). However, the precise alterations induced by reactive oxygen species or the specific species that are responsible for the derangements in skeletal muscle function are incom pletely understood. In this study, we evaluated the effect of the superoxid e anion radical (O-2(-.)), hydroxyl radical (. OH), and hydrogen peroxide ( H2O2) on maximum calcium-activated force (F-max) and calcium sensitivity of the contractile apparatus in chemically skinned (Triton X-100) single rat diaphragm fibers. O-2(-.) was generated using the xanthine/xanthine oxidase system; . OH was generated using 1 mM FeCl2, 1 mM ascorbate, and 1 mM H2O2 ; and H2O2 was added directly to the bathing medium. Exposure to O-2(-.) or . OH significantly decreased F-max by 14.5% (P < 0.05) and 43.9% (P < 0.00 5), respectively. . OH had no effect on Ca2+ sensitivity. Neither 10 nor 1, 000 muM H2O2 significantly altered F-max or Ca2+ sensitivity. We conclude t hat the diaphragm is susceptible to alterations induced by a direct effect of . OH and O-2(-.), but not H2O2, on the contractile proteins, which could , in part, be responsible for prolonged depression in contractility associa ted with respiratory muscle dysfunction in certain pathophysiological condi tions.