[Role of sodium ions in the protective action of nucleotides and their hydrolytic products in calcium paradox].

Nucleotides were examined for their effects on the development of calcium paradox in the isolated rat heart. The protective action of nucleotides was found to be unassociated with the structure of their nitrogen base. The products of extracellular hydrolysis, such as ribose (deoxyribose), uridine or adenosine at a concentration of 100 microM caused no less protective effects than nucleotides. In calcium paradox, the protective action of adenosine was not suppressed by theophylline, but sensitive to dipyridamole and transmembrane Na gradient values. Nucleotides and their hydrolytic products were demonstrated to exert a positive myocardial effect not only at the physiological (140 microM), but increased Na ion concentrations. The high extracellular Na concentration-induced potentiation of the protective action of nucleotides or their hydrolytic products was blocked by strophanthin. It is suggested that the high Na gradient can increase the protective action of nucleotides and their hydrolytic products due to decreased Na-Ca metabolism and to the altered metabolism of nucleotide hydrolytic products.