Preconditioning with diazoxide prevents reoxygenation-induced rigor-type hypercontracture

Ischemic preconditioning has a powerful protective potential against a reperfusion-induced injury of the post-ischemic myocardium. Cardiomyocyte hypercontracture, i.e. excessive cell shortening, is an essential mechanism of the reperfusion-induced injury. Rigor contracture, i.e. Ca2+-independent contracture, has been shown to be an import component of the reperfusion-induced hypercontracture. Since rigor contracture is dependent on the rapidity of the metabolic recovery during reoxygenation, we hypothesized that preconditioning of the cardiomyocyte mitochondria may improve mitochondrial function to restore the energy balance during the initial phase of reoxygenation and may thus prevent rigor contracture. For this purpose adult rat cardiomyocytes were exposed to anoxia with subsequent reoxygenation. For preconditioning, cells were pre-treated with the mitochondrial ATP-sensitive K+ channel opener diazoxide. Pre-treatment with 100 μmol/l diazoxide significantly reduced the reoxygenation-induced hypercontracture of cardiomyocytes due to an attenuation of the Ca2+-independent rigor-type contracture, which was accompanied by an acceleration of the phosphocreatine resynthesis during the initial phase of reoxygenation. Treatment with the mitochondrial ATP-sensitive K+ channel antagonist 5-hydroxydecanoate (500 μmol/l) during preconditioning phase abolished these protective effects. Similarly, partial suppression of the mitochondrial function with 100 μmol/l NaCN during the reoxygenation phase abolished the diazoxide effects. Finally, in isolated rat hearts, preconditioning with diazoxide prior to global ischemia significantly improved left ventricular function and attenuated hypercontracture during reperfusion. This effect could be abolished by the treatment with 100 μmol/l NaCN during reperfusion. Taken together, pharmacological preconditioning of cardiomyocytes with diazoxide protects against the reoxygenation-induced rigor hypercontracture due to an improvement of the energy recovery at the onset of reoxygenation.