The effect of calcium on myocardial lactate production under aerobic conditions

Abstract

In an isolated rat heart preparation allowing the determination of substrate utilization and production as well as of exact haemodynamic parameters the effect of varying the calcium concentration (3.9 m m and 1.95 m m) was studied. According to the decreased contractility in the low-calcium series, the mean values of P LV, of [ dp dt ] LV max and of Q O 2 were significantly lower than in the high calcium hearts. Similarly, glucose uptake was essentially higher in the high-calcium hearts than in the low-calcium series. The difference in lactate production was of special interest because the p O 2 of the perfusate was equally high in both series: the percentage of glucose consumed appearing in the perfusate as lactate (expressed in glucose-equivalents) was 32.5% in the low-calcium and 14.8% in the high calcium hearts. These results suggest that lactate production is not only increased under anaerobic conditions—when high energy phosphate levels are extremely low—but also in insufficiency of utilization brought about by reduced calcium availability—when high energy phosphate levels have been demonstrated to be increased.