Protection by benzamil against dysfunction and damage in rat myocardium after calcium depletion and repletion

Protection against cellular damage in the perfused rat heart by lowered pH

In this comparative study, rat hearts were perfused at 37 degrees C with three clearly defined protocols: the Ca2+ paradox, the O2 paradox and with 20 mM caffeine. Each protocol involved an initial priming (Ca2+(o) depletion or anoxia; stage 1) and subsequent full activation (Ca2+(o) repletion or reoxygenation; stage 2) of the damage system of the sarcolemma. Creatine kinase release in stage 2 was completely inhibited (P < 0.001) in all three protocols when pH was reduced to 6.5 throughout the experiments, or only during stage 1, or only during stage 2. The inhibitor of the Na+/H+ antiporter, amiloride (1 mM), completely prevented creatine kinase release in the Ca2+ paradox (P < 0.001) and markedly reduced damage in the caffeine protocol. Amiloride had no significant effect on creatine kinase release in the O2 paradox. The possible role of Na+(i) was studied in the caffeine protocol: ouabain (5 x 10(-6) M) had little effect whereas substitution of choline for Na+ in the perfusion medium reduced creatine kinase release by about 50%. It is suggested that the same damage system is activated in stage 1 in all three protocols and that a key event is the intracellular production of H+ which are exported via Na+(o)/H(i) exchange. Prevention of H+ efflux by lowered pH(o), even during stage 2, protected against creatine kinase release. The possible role of Na+ movements in the genesis of sarcolemma damage is discussed.

Hoe 694, a new Na+/H+ exchange inhibitor and its effects in cardiac ischaemia

1. The benzoylguanidine derivative Hoe 694 ((3-methylsulphonyl-4- piperidino-benzoyl) guanidine methanesulphonate) was characterized as an inhibitor of Na+/H+ exchange in rabbit erythrocytes, rat platelets and bovine endothelial cells. The potency of the compound was slightly lower or comparable to ethylisopropyl amiloride (EIPA). 2. To investigate a possible cardioprotective role of the Na+/H+ exchange inhibitor Hoe 694, rat isolated working hearts were subjected to ischaemia and reperfusion. In these experiments all untreated hearts suffered ventricular fibrillation on reperfusion. Addition of 10(-7) M Hoe 694 to the perfusate almost abolished reperfusion arrhythmias in the rat isolated working hearts. 3. Hoe 694 reduced the release of lactate dehydrogenase (LDH) and creatine kinase (CK), which are indicators of cellular damage during ischaemia, into the venous effluent of the hearts by 60% and 54%, respectively. 4. The tissue content of glycogen at the end of the experiments was increased by 60% and the high energy phosphates ATP and creatine phosphate were increased by 240% and 270% respectively in the treated hearts as compared to control hearts. 5. Antiischaemic effects of the Na+/H+ exchange inhibitor, Hoe 694, were investigated in a second experiment in anaesthetized rats undergoing coronary artery ligation. In these animals, pretreatment with Hoe 694 caused a dose-dependent reduction of ventricular premature beats and ventricular tachycardia as well as a complete suppression of ventricular fibrillation down to doses of 0.1 mg kg-1, i.v. Blood pressure and heart rate remained unchanged. 6. We conclude that the new Na+/H+ exchange inhibitor, Hoe 694, shows cardioprotective and antiarrhythmic effects in ischaemia and reperfusion in rat isolated hearts and in anaesthetized rats. In view of the role which Na+/H+ exchange seems to play in the pathophysiology of cardiac ischaemia these effects could probably be attributed to Na+/H+ exchange inhibition.