ULTRASTRUCTURAL-STUDY OF CALCIUM SHIFT IN ISCHEMIC REPERFUSED RAT-HEART UNDER TREATMENT WITH DIMETHYLTHIOUREA, DILTIAZEM AND AMILORIDE/

Among factors underlying reperfusion injury are oxygen free radicals a nd Ca2+ influx via gated calcium channel or via Na+/H+ - Na+/Ca2+ exch ange which lead to calcium overload. The aim of the study was to ultra structurally visualize the distribution of Ca2+ and to compare binding of calcium by the sarcolemma and calcium accumulation in mitochondria under therapy with an . OH scavenger, dimethylthiourea (DMTU), Na+/H exchange inhibitor, amiloride, and calcium channel blocker, diltiazem , given alone or in combination to ischemic/reperfused hearts. Isolate d working hearts subjected to 40 min ischemia and 30 min reperfusion w ere perfused with drugs added to the perfusate 15 min before ischemia and administered for the rest of the perfusion period. The cytochemica l phosphate pyroantimonate method for localization of Ca2+ was used, a nd calcium distribution was analyzed with a computer image analyzer. A ll drugs given alone improved sarcolemmal ability to bind calcium. The best results were obtained with amiloride. All of the combined therap ies gave even better results, but calcium accumulation in mitochondria diminished only with diltiazem therapy given alone or in combination with DMTU. Since the presence of Ca2+ deposits on the sarcolemma is be lieved to represent its normal function, and calcium sequestration by mitochondria reflects an increase in cytosolic calcium load, the lack of correlation between sarcolemmal and mitochondrial Ca2+ distribution might suggest impaired mechanisms of lowering cytoplasmic calcium or the existence of some mechanism other than Na+/Ca2+ exchange, mediated by activated Na+/H+ exchange.