Ca2+‐induced mitochondrial permeability transition pore opening is substrate‐dependent

Abstract

Mitochondrial permeability transition pore (mPTP) opening is a key event in ischemia and reperfusion (I/R) injury. Several factors modulate mPTP opening, of which the increase in mitochondrial free Ca2+ plays a critical role. During I/R, there is a substrate switch in mitochondria and it is not known with certainty if/how substrate conditions influence mPTP opening. Hence, we investigated Ca2+‐induced mPTP opening by monitoring Ca2+ retention capacity (CRC) under different substrate conditions. Guinea pig heart mitochondria were suspended in respiration media containing rhodamine 123 or indo‐1 to monitor changes in ΔΨ or extra matrix [Ca2+], respectively. Either pyruvate or succinate was added first, followed by continuous infusion of CaCl2. ΔΨ became depolarized at 275±25 s or at 687±37 s with pyruvate or succinate, respectively. Indo‐1 experiments showed mitochondrial Ca2+ release in the buffer that paralleled ΔΨ depolarization. Adding cyclosporine A prolonged CRC with both substrates indicating that ΔΨ depolarization and Ca2+ release were due to mPTP opening. It is widely accepted that mPTP opening occurs upon reperfusion due to normalization of cytosolic pH. However, our results suggest a role for the complex I substrate pyruvate in Ca2+‐induced mPTP opening and thus, mitochondrial utilization of succinate during reperfusion may prove beneficial against mPTP opening.