Beneficial effect of taurine depletion on osmotic sodium and calcium loading during chemical hypoxia

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Abstract
Cellular sodium excess is cytotoxic because it increases both the intracellular osmotic load and intracellular calcium concentration ([Ca2+]i). Because sodium levels rise during hypoxia, it is thought to contribute to hypoxic injury. Thus the present study tested the hypothesis that taurine-linked reductions in [Na+]ireduce hypoxia-induced cell injury. Taurine depletion was achieved by exposing isolated neonatal cardiomyocytes to medium containing the taurine analog β-Alanine. As predicted, the β-Alanine-treated cell exhibited less hypoxia-induced necrosis and apoptosis than the control, as evidenced by less swelling, shrinkage, TdT-mediated dUTP nick end labeling staining, and accumulation of trypan blue. After 1 h of chemical hypoxia, [Na+]iwas 3.5-fold greater in the control than the taurine-deficient cell. Although more taurine was lost from the control cell than from the β-Alanine-treated cell during hypoxia, the combined taurine and sodium osmotic load was lower in the β-Alanine-treated cell. Taurine deficiency also reduced the degree of hypoxia-induced calcium overload. Thus the observed resistance against hypoxia-induced necrosis and apoptosis is probably related to an improvement in sodium and calcium handling.