ABSTRACT
Long-chain nonesterified fatty acids are major substrates for myocardial energy production. Lactate is a predominant oxidative substrate for the myocardium and isolated cardiomyocytes. The transport of lactate into the isolated myocardial cell has been analyzed by Kammermeier et al. Formation of lactate in hearts at low work load under conditions where inhibitory effects of other physiological substrates on glycolytic flux are eliminated indicates that the coupling of glycolytic flux rates to the turnover rate of the tricarboxylic acid cycle is only loose unless glycolytic flux becomes rate limiting. In comparison to other substrates in physiological concentration, fatty acids are also the most preferred substrate for the isolated heart muscle cell. Substrate metabolism of isolated heart cells in suspension has been characterized in a number of studies. The heart cell is incapable of synthesizing carnitine, but if otherwise healthy, it will actively take up carnitine if supplied with the surrounding medium.
