HYPOCHLOROUS ACID INHIBITS CA2+-ATPASE ACTIVITY FROM SKELETAL MUSCLE SARCOPLASMIC RETICULUM 1286

Abstract

Hypochlorous acid (HOCl) is produced by polymorphonuclear leukocytes that migrate and adhere to endothelial cells as part of the inflammatory process. HOCl is an extremely toxic oxidant that can react with a variety of cellular components. Concentrations have been reported as high as 200 uM in some tissues. Recent reports have indicated that myeloperoxidase, the enzyme that produces HOCl, is activated during and following submaximal bouts of exercise. In this study we show that HOCl inhibits SR Ca2+-ATPase activity. Following a 10 minute exposure, ATPase activity declined in a concentration dependent manner with an IC50 of 170 uM and complete inhibition by 3 mM. A reduction of ATP stimulated Ca2+ uptake into SR vesicles paralled the decline in ATPase activity. A concommitent reduction in free sulfhydryl groups (20.1 to 7.2 mol/mol protein) accompanied the HOCl induced inhibition of ATPase activity. HOCl also inhibited the FITC binding, indicating alterations in the structural integrity of the adenine nucleotide binding pocket. These findings suggest that the reactive oxygen specie, HOCl inhibits ATPase activity via a modification of endogenous SH groups supporting the contention that ROS disrupt normal Ca2+ handling in muscle cells.