Functional crosstalk between the mitochondrial PTP and K(ATP) channels determine arrhythmic vulnerability to oxidative stress

Background: Mitochondrial permeability transition pore (mPTP) opening is a terminal event leading to mitochondrial dysfunction and cell death under conditions of oxidative stress (OS). However, mPTP blockade with cyclosporine A (CsA) has shown variable efficacy in limiting post-ischemic dysfunction and arrhythmias. We hypothesized that strong feedback between energy dissipating (mPTP) and cardioprotective (mK(ATP)) channels determine vulnerability to OS. Methods and Results: Guinea pig hearts (N = 61) were challenged with H(2)O(2) (200 μM) to elicit mitochondrial membrane potential (ΔΨ(m)) depolarization. High-resolution optical mapping was used to measure ΔΨ(m) or action potentials (AP) across the intact heart. Hearts were treated with CsA (0.1 μM) under conditions that altered the activity of mK(ATP) channels either directly or indirectly via its regulation by protein kinase C. mPTP blockade with CsA markedly blunted (P < 0.01) OS-induced ΔΨ(m) depolarization and delayed loss of LV pressure (LVP), but did not affect arrhythmia propensity. Surprisingly, prevention of mK(ATP) activation with the chemical phosphatase BDM reversed the protective effect of CsA, paradoxically exacerbating OS-induced ΔΨ(m) depolarization and accelerating arrhythmia onset in CsA treated compared to untreated hearts (P < 0.05). To elucidate the putative molecular mechanisms, mPTP inhibition by CsA was tested during conditions of selective PKC inhibition or direct mK(ATP) channel activation or blockade. Similar to BDM, the specific PKC inhibitor, CHE (10 μM) did not alter OS-induced ΔΨ(m) depolarization directly. However, it completely abrogated CsA-mediated protection against OS. Direct pharmacological blockade of mK(ATP), a mitochondrial target of PKC signaling, equally abolished the protective effect of CsA on ΔΨ(m) depolarization, whereas channel activation with 30 μM Diazoxide protected against ΔΨ(m) depolarization (P < 0.0001). Conditions that prevented mK(ATP) activation either directly or indirectly via PKC inhibition led to accelerated ΔΨ(m) depolarization and early onset of VF in response to OS. Investigation of the electrophysiological substrate revealed accelerated APD shortening in response to OS in arrhythmia-prone hearts. Conclusions: Cardioprotection by CsA requires mK(ATP) channel activation through a PKC-dependent pathway. Increasing mK(ATP) activity during CsA administration is required for limiting OS-induced electrical dysfunction.