Protection of ischemic rat heart by dantrolene, an antagonist of the sarcoplasmic reticulum calcium release channel

Cytosolic Ca2+ overload plays a major role in the development of irreversib le injury during myocardial ischemia. Such overload is due at least in part to the release of Ca2+ from the sarcoplasmic reticulum. Therefore, we inve stigated whether dantrolene, a blocker of the sarcoplasmic reticulum Ca2+ r elease channel, may protect from ischemic injury. In binding experiments, w e determined the effect of dantrolene on [H-3]-ryanodine binding in rat car diac tissue. In perfusion experiments, isolated rat hearts were perfused fo r 20 min in the working mode, in the presence of 0-45 mu M dantrolene. The hearts were then subjected to 30 min of global ischemia and 120 min of retr ograde reperfusion. Tissue injury was evaluated on the basis of triphenylte trazolium chloride (TTC) staining and LDH release. The binding experiments showed that dantrolene displaced 4 nM [H-3]-ryanodine with IC50 of 34 mu M In the perfusion experiments, tissue necrosis (i.e., TTC-negative tissue) a veraged 28.3 +/- 1.6 % of the ventricular mass under control conditions. Da ntrolene was protective at micromolar concentrations: tissue necrosis decre ased to 21.4 +/- 1.0 % and 8.4 +/- 1.4 % with 1 mu M and 45 mu M dantrolene , respectively (P < 0.05 and P < 0.01). Similar results were obtained with regard to LDH release. At low concentrations (up to 4 mu M), dantrolene did not produce any significant hemodynamic effect, except for a slight increa se in coronary flow, whereas at higher concentration a negative inotropic e ffect was apparent. In conclusion, dantrolene reduced ischemic injury even at concentrations that did not affect contractile performance. Modulation o f sarcoplasmic reticulum Ca2+ release might represent a new cardioprotectiv e strategy.