Cardiology Letters 2014, 23(3):228-233

The role of mitochondria in preconditioning of heart induced by diazoxide. New insight into the molecular mechanism

Jašová M¹, Ferko M¹, Kancirová I¹, Muráriková M¹, Námer P², Waczulíková I³, Slezák J^{1, 4}, Ziegelhöffer A¹

¹ Ústav pre výskum srdca SAV, Centrum excelentnosti kardiovaskulárnych vied

² Ústav polymérov SAV, Bratislava

³ Katedra jadrovej fyziky a biofyziky, Fakulta matematiky, fyziky a informatiky, Univerzita Komenského v Bratislave

⁴ Slovenská zdravotnícka univerzita v Bratislave, Slovenská republika

Diazoxide (DZX), which was assumed to act predominantly as an opener of the ATP-dependent potassium channels (KATP) in mitochondrial membranes, is frequently utilised in the induction of pharmacological preconditioning of the myocardium in an experiment. However, recent findings have revealed that DZX acts more as an activator of the protein kinase Cε (PKCε) and that opening of the mitochondrial KATP channels is its secondary effect only. Moreover, DZX also acts as an inhibitor of the Krebs cycle at the level of succinate dehydrogenase. A similar type of inhibition also occurs in hypoxia and ischemia. The aim of our study was to search for such an effect of DZX on the mitochondria, which supposedly is directly responsible for the contribution of mitochondria to an increased ischemic tolerance of the myocardium. Experiments were performed on isolated heart mitochondria from 9-11 weeks old male Wistar rats exposed to the effect of DZX concentrations in the range of 0-7 μmol.l-1. Starting with the concentration of 3.5 μmol.l-1 DZX induced a dose-dependent increase in the activity of the mitochondrial Mg2+-ATPase (the mitochondrial ATP synthase was estimated in a reversed direction of its reaction), expressed in μmol of the inorganic phosphate liberated by ATP splitting x mg mitochondrial protein-1 x h-1. Increase in the enzyme activity reached statistical significance (p<0.05) at the DZX concentrations of 5, 6 and 7 μmol.l-1 and it was not accompanied by any considerable change in fluidity of the mitochondrial membrane. This pointed to a direct interaction of DZX with the enzyme molecule. Investigation by means of enzyme kinetics confirmed a direct, non-competitive stimulatory effect of DZX on the activity of the mitochondrial Mg2+-ATPase. Results indicate that the improved production of energy, enabled via stimulation of the Mg2+-ATPase activity, represents a direct mechanism by which heart mitochondria may participate in the DZX-induced preconditioning of the myocardium.

Keywords: mitochondria; diazoxide; preconditioning; membrane fluidity; mitochondrial Mg2+-ATPase

Published: March 1, 2014  Show citation