MECHANISMS OF MYOCARDIAL PROTECTION BY AMINO-ACIDS - FACTS AND HYPOTHESES

1. Positive inotropic effect of taurine and improvement of cardiac per formance of failing heart are mediated through the modulation of Ca2movement through the sarcolemma. 2. Cardioprotection with glutamate an d aspartate is related to enhanced anaerobic energy formation in mitoc hondria coupled with succinate formation and, probably, with the relie ving of glycolytic flux. During reperfusion, both amino acids replenis h the malate-aspartate shuttle reactants, thereby facilitating glucose oxidation. 3. Increased intracellular concentrations of branched chai n amino acids (leucine, valine and isoleusine) stimulate formation of acetyl-coenzyme (CoA) and succinyl-CoA and, thus, recovery of oxidativ e metabolism. 4. Methionine and cysteine enhance force of contraction by N-methylation of membrane phospholipids of the sarcolemma and sarco plasmic reticulum. Methionine and, to a lesser extent, cysteine may re duce myocardial damage by oxygen radical species. 5. Histidine exerts antioxidant properties as a scavenger of singlet oxygen and OH. radica ls. High concentrations of histidine provide intracellular buffering t o stimulate anaerobic energy formation.