Isoflurane protects cardiomyocytes and mitochondria by immediate and cytosol-independent action at reperfusion

Background and purpose:

The volatile anaesthetic isoflurane protects the heart from ischaemia and reperfusion (I/R) injury when applied at the onset of reperfusion [anaesthetic postconditioning (APoC)]. However, the mechanism of APoC-mediated protection is unknown. In this study, we examined the effect of APoC on mitochondrial bioenergetics, mitochondrial matrix pH (pH_m) and cytosolic pH (pH_i), and intracellular Ca²⁺.

Experimental approach:

Cardiac mitochondria from Wistar rats were isolated after in vivo I/R with or without APoC (1.4%-vol isoflurane, 1 minimum alveolar concentration), and mitochondrial permeability transition pore (mPTP) opening, mitochondrial membrane potential (ΔΨ_m), and oxygen consumption were assessed. In isolated cardiomyocytes and isolated mitochondria I/R injury was produced in vitro, with or without APoC (0.5 mM isoflurane). Intracellular Ca²⁺, pH_m, pH_i and ΔΨ_m were monitored with SNARF-1, TMRE and fluo-4, respectively. Myocyte survival was assessed when APoC was induced at pH 7.4 and 7.8. In isolated mitochondria oxygen consumption and ATP synthesis were measured.

Key results:

In vivo APoC protected against mPTP opening, slowed mitochondrial respiration and depolarized mitochondria. APoC decreased the number of hypercontracted cardiomyocytes at pH 7.4, but not at pH 7.8. APoC attenuated intracellular Ca²⁺ accumulation, maintained lower pH_m, and preserved ΔΨ_m during reoxygenation. Isoflurane did not affect the regulation of cytosolic pH. In mitochondria, APoC preserved ATP production rate and respiration.

Conclusions and implications:

At reperfusion, APoC inhibited mitochondrial respiration, depolarized mitochondria and acidified pH_m. These events may lead to inhibition of mPTP opening and, consequently, to preserved ΔΨ_m and ATP synthesis. This reduces intracellular Ca²⁺ overload and cell death.This article is commented on by Moncada, pp. 217–219 of this issue. To view this commentary visit http://dx.doi.org/10.1111/j.1476-5381.2010.00706.x and to view related papers in this issue by Puerta et al. and Kurz et al. visit http://dx.doi.org/10.1111/j.1476-5381.2010.00663.x and http://dx.doi.org/10.1111/j.1476-5381.2010.00656.x