Investigating the inotropic effect of pyruvic acid on the isolated rat heart and its underlying mechanism

Pyruvic acid is important organic chemical intermediates that plays a role in cardiomyocyte pathophysiology and therapy. This study sought to explore the inotropic effects of pyruvic acid on the function of the isolated rat hearts and investigate its underlying mechanism. Pyruvic acid produced a greater negative inotropic effect compared to HCl and sodium pyruvate in a concentration-dependent pattern in the hearts. The role of low dose of pyruvic acid on heart function was regulated by pyruvic acid molecules and high dose pyruvic acid may be influenced by pyruvic acid molecules and pH. K_v channels may be involved in the pyruvic acid-induced negative inotropic effect. Finally, pyruvic acid markedly increased the level of LDH and CK and reduced the level of Ca²⁺Mg²⁺-ATPase and Na⁺K⁺-ATPase. These results suggest that pyruvic acid may modulate cardiac function at physiological or low doses but can cause damage to cardiomyocytes at high doses.

A defect in the acetyl coenzyme A<-->acetate pathway poisons recombinational repair-deficient mutants of Escherichia coli

Recombinational repair-dependent mutants identify ways to avoid chromosomal lesions. Starting with a recBC(Ts) strain of Escherichia coli, we looked for mutants unable to grow at 42 degrees C in conditions that inactivate the RecBCD(Ts) enzyme. We isolated insertions in ackA and pta, which comprise a two-gene operon responsible for the acetate<-->acetyl coenzyme A interconversion. Using precise deletions of either ackA or pta, we showed that either mutation makes E. coli cells dependent on RecA or RecBCD enzymes at high temperature, suggesting dependence on recombinational repair rather than on the RecBCD-catalyzed linear DNA degradation. Complete inhibition of growth of pta/ackA rec mutants was observed only in the presence of nearby growing cells, indicating cross-inhibition. pta rec mutants were sensitive to products of the mixed-acid fermentation of pyruvate, yet none of these substances inhibited growth of the double mutants in low-millimolar concentrations. pta, but not ackA, mutants also depend on late recombinational repair functions RuvABC or RecG. pta/ackA recF mutants are viable, suggesting, together with the inviability of pta/ackA recBC mutants, that chromosomal lesions due to the pta/ackA defect are of the double-strand-break type. We have isolated three insertional suppressors that allow slow growth of pta recBC(Ts) cells under nonpermissive conditions; all three are in or near genes with unknown functions. Although they do not form colonies, ackA rec and pta rec mutants are not killed under the nonpermissive conditions, exemplifying a case of synthetic inhibition rather than synthetic lethality.