Cardiostimulatory action of coenzyme Q homologues on cultured myocardial cells and their biochemical mechanisms

Summary The effect of coenzyme Q (CoQ) homologues on the beating of myocardial cells was investigated in cultured cell sheets from mouse fetuses and quail embryos. Myocardial cell sheets grown in Eagle's minimum essential medium with fetal bovine serum showed very weak and irregular beating when this serum was removed from the medium. However, the depressed beating rate and amplitude recovered almost completely within a few minutes by adding CoQ₁₀ to the medium, and the effect of Co₁₀ continued over 1 h. CoQ₉ showed a cardiostimulatory effect similar to that of CoQ₁₀ but CoQ₈ and COQ₇ showed almost no effect. Short homologues (less than CoQ₄) inhibited the beating of cell sheets. The cardiostimulatory effect of CoQ₁₀ was not blocked by atenolol, a selective ß-blocker. In addition, CoQ₁₀ stimulated the formation of ATP, not cAMP. CoQ₀ and COQ₃ inhibited beating rates by inhibiting ATP formation. In conclusion, only native CoQ homologues having a nona- or decaprenyl group showed a cardiostimulatory effect on cultured myocardial cells, probably by stimulating mitochondrial ATP formation.