EFFECTS OF HYDROGEN-PEROXIDE ON MEMBRANE FLUIDITY AND CA(2-TRANSPORTING ATPASE ACTIVITY OF RABBIT MYOCARDIAL SARCOPLASMIC-RETICULUM())

This study was to investigate the effects of hydrogen peroxide on memb rane fluidity and Ca2+-ATPase activity of rabbit myocardial sarcoplasm ic reticulum (SR). The membrane fluidity of SR was monitored by measur ing the changes in the steady state fluorescence anisotropies (r(s)) u sing diphenylhexatriene as a probe. The Ca2+-ATPase activity was deter mined by assaying the amount of inorganic phosphate (P(i)) released fr om ATP. It was found that the membrane fluidity (r(s): 0.154 +/- 0.014 vs 0.113 +/- 0.010, P < 0.01) and Ca2+-ATPase activity (3.1 +/- 1.3 v s 25.3 +/- 2.4 mumol P(i) . h-1/mg protein, P < 0.01 ) were reduced i n SR exposed to H2O2 (2 mmol . L-1) for 40 min. Catalase 20 mug . ml-1 completely prevented the SR damages caused by H2O2. H2O2 jeopardized the SR in a concentration- and time-dependent manner as measured by ch anges in r(s) values and Ca2+-ATPase activities, which were negatively correlated (r = 0.981, P < 0.01). These results suggest that H2O2 pro duces dysfunctions of the rabbit myocardial SR, and that the alteratio n of membrane fluidity may be one of the mechanisms responsible for th e decrease of Ca2+-ATPase activity.