Hypochlorous acid inhibits Ca2+-ATPase from skeletal muscle sarcoplasmic reticulum

Favero, Terence G., David Colter, Paul F. Hooper, andJonathan J. Abramson. Hypochlorous acid inhibitsCa²⁺-ATPase from skeletal musclesarcoplasmic reticulum. J. Appl. Physiol. 84(2): 425-430, 1998.Hypochlorous acid(HOCl) is produced by polymorphonuclear leukocytes that migrate andadhere to endothelial cells as part of the inflammatory response totissue injury. HOCl is an extremely toxic oxidant that can react with avariety of cellular components, and concentrations reaching 200 µMhave been reported in some tissues. In this study, we show that HOClinteracts with the skeletal sarcoplasmic reticulumCa²⁺-adenosinetriphosphatase(ATPase), inhibiting transport function. HOCl inhibits sarcoplasmicreticulum Ca²⁺-ATPase activity ina concentration-dependent manner with a concentration required toinhibit ATPase activity by 50% of 170 µM and with completeinhibition of activity at 3 mM. A concomitant reduction infree sulfhydryl groups after HOCl treatment was observed, paralleling the inhibition of ATPase activity. It was also observed that HOCl inhibited the binding of the fluorescent probe fluoresceinisothiocyanate to the ATPase protein, indicating some structural damagemay have occurred. These findings suggest that the reactive oxygenspecies HOCl inhibits ATPase activity via a modification of sulfhydryl groups on the protein, supporting the contention that reactive oxygenspecies disrupt the normalCa²⁺-handling kinetics in musclecells.