Alteration in Cardiac Sarcolemmal ATP Receptors by Oxyradicalsa

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Abstract
We previously demonstrated that cardiac sarcolemmal membranes bind [35S]ATP gamma S at both low and high affinity binding sites. In this study we examined the effects of some P2-purinoceptor antagonists as well as of two oxidants (H2O2 and HOCl) on the high affinity ATP-binding sites under in vitro conditions. It was found that putative P2-purinoceptor antagonists such as Cibacron blue, suramin, and 4,4'-diisothiocyanatostilbene 2-2 acid markedly inhibited specific ATP-binding with sarcolemmal membrane. H2O2 produced a biphasic effect (first increase and then decrease) on the specific ATP-binding with cardiac sarcolemma in a time- and concentration-dependent manner; these effects were prevented by catalase. On the other hand, HOCl markedly inhibited ATP-binding; this inhibition was prevented by l-methionine. These results suggest that the high affinity ATP-binding sites in cardiac sarcolemma may represent the P2-purinoceptors, which are susceptible to modification by oxidative stress under pathophysiological conditions including myocardial ischemia-reperfusion injury.