Mitochondrial Depolarization Is Not responsible for Cardioprotection During Ischemic Preconditioning

Abstract

Mitochondrial (mito) respiratory electron transfer chain (RTC) is a major source of reactive oxygen species (ROS) during ischemia reperfusion (IR). Mito membrane potential (Δψ) may affect ROS production by changing the redox status of the RTC. Mild uncoupling can lead to oxidation of the RTC and decrease ROS production. It is unclear how ischemic preconditioning (IPC) decreases mito ROS generation. We examined the changes in mito Δψ and its correlation to ROS production in IR and IPC mito.Isolated rat hearts (n=6/group) were subjected to 1) CONTROL: 30 minutes (min) of equilibration (EQ), 30 min of ischemia (I), and 30 min of reperfusion (RP), or 2) IPC: 10 min of EQ, two 5 min episodes of I and RP, 30 min of I, and 30 min of RP. Mitos were isolated at end I and end RP. ROS production was assessed by EPR spectroscopy using DMPO as spin trap. Δψ was measured using a TPP electrode. Data is expressed as mean±sem. ROS production by Complex I & III (arbitrary units/mg protein) Δψ (‐mV) End I End RP End I End RP CONTROL 2220±22 3524±340 121±8 150±2 IPC 1878±175 2479±296* 147±7* 160±3* p<0.05 vs. CONTROL Ischemia led to lower Δψ in IPC and CONTROL. Δψ recovered during reperfusion. However, Δψ remained higher in IPC at end I and end RP. IPC decreases ROS production during RP. Membrane depolarization was not associated with lower ROS production. We conclude that membrane depolarization is not responsible for the cardioprotective effect of IPC.