The Positive Inotropic Effect of Pyruvate Involves an Increase in Myofilament Calcium Sensitivity

Abstract

Pyruvate is a metabolic fuel that is a potent inotropic agent. Despite its unique inotropic and antioxidant properties, the molecular mechanism of its inotropic mechanism is still largely unknown. To examine the inotropic effect of pyruvate in parallel with intracellular calcium handling under near physiological conditions, we measured pH, myofilament calcium sensitivity, developed force, and calcium transients in ultra thin rabbit heart trabeculae at 37 °C loaded iontophoretically with the calcium indicator bis-fura-2. By contrasting conditions of control versus sarcoplasmic reticulum block (with either cyclopiazonic acid and ryanodine or with thapsigargin) we were able to characterize and isolate the effects of pyruvate on sarcoplasmic reticulum calcium handling and developed force. A potassium contracture technique was subsequently utilized to assess the force-calcium relationship and thus the myofilament calcium sensitivity. Pyruvate consistently increased developed force whether or not the sarcoplasmic reticulum was blocked (16.8±3.5 to 24.5±5.1 vs. 6.9±2.6 to 12.5±4.4 mN/mm2, non-blocked vs. blocked sarcoplasmic reticulum respectively, p<0.001, n = 9). Furthermore, the sensitizing effect of pyruvate on the myofilaments was demonstrated by potassium contractures (EC50 at baseline versus 20 minutes of pyruvate infusion (peak force development) was 701±94 vs. 445±65 nM, p<0.01, n = 6). This study is the first to demonstrate that a leftward shift in myofilament calcium sensitivity is an important mediator of the inotropic effect of pyruvate. This finding can have important implications for future development of therapeutic strategies in the management of heart failure.

Effects of pyruvate on the energetics of rat ventricles stunned by ischemia–reperfusion

“…2a) is in accordance to the tendency found in other reports (Kerr et al 1999;Diolez et al 2007). However, some studies found that Pyr is a positive inotropic agent in several species, e.g., rabbit and human (Leite-Moreira et al 2002;Keweloh et al 2007;Torres et al 2013), dog (Mentzer et al 1989;Yanos et al 1994), guinea-pig (Daut and Elzinga 1989), and rat (Martin et al 1998), while others did not find any inotropic change in rat hearts (Ojha et al 2012). This difference in behavior can be attributed to several factors, such as in vivo vs. in vitro experiments, temperature, and concentration.…”

“…The temperature-dependence of Pyr effect may be the result of a balance among its several cellular effects. At a physiological temperature, the positive inotropism of Pyr suggests the predominance of mechanisms activated by the rise in aerobic metabolism, such as phosphorylation potential, SR Ca 2+ store, and myofilament Ca 2+ sensitivity (Zima et al 2003;Mallet et al 2005;Torres et al 2013). They would be exceeding the negative Fig.…”

A technical review of optical mapping of intracellular calcium within myocardial tissue

“…Even though fura 4F has not yet been used in optical mapping experiments, sophisticated multiparametric optical mapping systems are being developed for ratiometric imaging of both high-and low-affinity Ca 2ϩ probes (36,56). Future studies of myocardial metabolism, where changes in Ca i 2ϩ , mitochondrial redox state, and mitochondrial membrane potential are measured (2,39,91,98), would certainly benefit from accurate measurements of relative changes in Ca i 2ϩ using ratiometry. Quantification of nonratiometric signals.…”

“…Ca i 2ϩ dynamics and metabolism. In metabolic studies, changes in Ca i 2ϩ kinetics that alter contractile function in perfused hearts are measured using Ca 2ϩ fluorescence probes (14,39,98). For example, paired optical mapping studies that measured developed pressure, NADH fluorescence, and Ca i 2ϩ transients in perfused rat hearts provided mechanistic insights into the inotropic effects of pyruvate and dichloroacetate, two compounds that promote full glucose oxidation in myocytes (39).…”

Functional response of the isolated, perfused normoxic heart to pyruvate dehydrogenase activation by dichloroacetate and pyruvate

“…Administering pyruvate would not correct an imbalance between glycolysis and full glucose oxidation: in fact, any imbalance would be exacerbated. Numerous other studies have investigated the mechanisms by which pyruvate improves cardiac function without the confounding variable of ischemia [10, 46, 52]; however, there are very few investigations of the mechanisms of DCA in the absence of ischemia.…”