Cariporide, a Highly Selective Na+/H+ Exchange Inhibitor, Suppresses the Reperfusion-Induced Lethal Arrhythmias and "Overshoot" Phenomenon of Creatine Phosphate In Situ Rat Heart

The effects of a highly selective Na+/H+ exchange inhibitor cariporide on the reperfused in situ heart were assessed. Male Sprague-Dawley (SD) rats weighing 200-300 g were anesthetized with pentobarbital sodium (60 mg/kg, i.p.) and divided into four groups; sham-operated (n = 6), vehicle (n = 15), 0.1 mg/kg (n = 15), and 1.0 mg/kg (n = 15) groups. The left coronary artery was ligated for 5 min and then released with ECG and blood pressure monitoring. Cariporide was intravenously given as a bolus 2 min before the reperfusion. The heart was rapidly excised and frozen 3 min after the onset of ventricular fibrillation, otherwise 10 min after the reperfusion. The adenosine triphosphate (ATP), creatine phosphate (CP), and glycogen contents were measured in the reperfused ischemic myocardium by using an enzymatic fluorometric assay technique. The incidence of the lethal ventricular fibrillation was 53% in the vehicle, 27% in the low-dose and 7% in the high-dose group. The concentrations (mean+/-SEM) of ATP, CP (nmol/mg protein), and glycogen (nmol as glucose/mg protein) were 74+/-4, 255+/-19, and 164+/-21 in the sham, 23+/-4, 763+/-70, and 61+/-7 in the vehicle, 27+/-4, 180+/-16, and 104+/-14 in the low-dose, and 32+/-4, 178+/-24, and 108+/-8 in the high-dose groups, respectively, indicating that cariporide significantly blunted CP overshoot as well as glycogenolysis during reperfusion. Thus cariporide can be expected to depress arrhythmogenesis and protect the metabolic status of the heart.