Calmodulin participation in oxygen radical-induced cardiac sarcoplasmic reticulum calcium uptake reduction

Abstract

The effect of scavengers of oxygen radicals on canine cardiac sarcoplasmic reticulum (SR) Ca 2+ uptake velocity was investigated at pH 6.4, the intracellular pH of the ischemic myocardium. With the generation of oxygen radicals from a xanthine-xanthine oxidase reaction, there was a significant depression of SR Ca 2+ uptake velocity. Xanthine alone or xanthine plus denatured xanthine oxidase had no effect on this system. Superoxide dismutase (SOD), a scavenger of .O 2 −, or denatured SOD had no effect on the depression of Ca 2+ uptake velocity induced by the xanthine-xanthine oxidase reaction. However, catalase, which can impair hydroxyl radical (.OH) formation by destroying the precursor H 2O 2, significantly inhibited the effect of the xanthine-xanthine oxidase reaction. This effect of catalase was enhanced by SOD, but not by denatured SOD. Dimethyl sulfoxide (Me 2SO), a known .OH scavenger, completely inhibited the effect of the xanthine-xanthine oxidase reaction. The observed effect of oxygen radicals and radical scavengers was not seen in the calmodulin-depleted SR vesicles. Addition of exogenous calmodulin, however, reproduced the effect of oxygen radicals and the scavengers. The effect of oxygen radicals was enhanced by the calmodulin antagonists (compounds 48 80 and W-7 ) at concentrations which showed no effect alone on Ca 2+ uptake velocity. Taken together, these findings strongly suggest that .OH, but not .O 2 −, is involved in a mechanism that may cause SR dysfunction, and that the effect of oxygen radicals is calmodulin dependent.