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

Abstract

Cytosolic Ca²⁺ overload plays a major role in the development of irreversible injury during myocardial ischemia. Such overload is due at least in part to the release of Ca²⁺ from the sarcoplasmic reticulum. Therefore, we investigated whether dantrolene, a blocker of the sarcoplasmic reticulum Ca²⁺ release channel, may protect from ischemic injury. In binding experiments, we determined the effect of dantrolene on [³H]-ryanodine binding in rat cardiac tissue. In perfusion experiments, isolated rat hearts were perfused for 20 min in the working mode, in the presence of 0–45 μM dantrolene. The hearts were then subjected to 30 min of global ischemia and 120 min of retrograde reperfusion. Tissue injury was evaluated on the basis of triphenyltetrazolium chloride (TTC) staining and LDH release. The binding experiments showed that dantrolene displaced 4 nM [³H]-ryanodine with IC₅₀ of 34 μM. In the perfusion experiments, tissue necrosis (i.e., TTC-negative tissue) averaged 28.3±1.6% of the ventricular mass under control conditions. Dantrolene was protective at micromolar concentrations: tissue necrosis decreased to 21.4±1.0% and 8.4±1.4% with 1 μM and 45 μM dantrolene, respectively (P < 0.05 and P < 0.01). Similar results were obtained with regard to LDH release. At low concentrations (up to 4 μM), dantrolene did not produce any significant hemodynamic effect, except for a slight increase in coronary flow, whereas at higher concentration a negative inotropic effect was apparent. In conclusion, dantrolene reduced ischemic injury even at concentrations that did not affect contractile performance. Modulation of sarcoplasmic reticulum Ca²⁺ release might represent a new cardioprotective strategy.