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 membrane fluidity and Ca2+-ATPase activity of rabbit myocardial sarcoplasmic reticulum (SR). The membrane fluidity of SR was monitored by measuring the changes in the steady state fluorescence anisotropies (r(s)) using diphenylhexatriene as a probe. The Ca2+-ATPase activity was determined by assaying the amount of inorganic phosphate (P(i)) released from 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 in 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 changes in r(s) values and Ca2+-ATPase activities, which were negatively correlated (r = 0.981, P < 0.01). These results suggest that H2O2 produces dysfunctions of the rabbit myocardial SR, and that the alteration of membrane fluidity may be one of the mechanisms responsible for the decrease of Ca2+-ATPase activity.