- Meeting abstract
- Open Access
Ischemia Time Impacts on Respiratory Chain Functions and Ca2+-Handling of Cardiac Subsarcolemmal Mitochondria Subjected to Ischemia Reperfusion Injury
Journal of Cardiothoracic Surgery volume 10, Article number: A126 (2015)
Significant mitochondrial function impairment is known to result from cardiac ischemia reperfusion injury (IR) precipitated by cardiopulmonary bypass during heart surgery.
We sought to determine the effect of different ischemia time spans in cardiac IR on mitochondrial respiratory chain (RC) function, inner membrane polarization and Ca2+homeostasis.
Wistar rat hearts were harvested and divided into 4 groups of stop-flow induced warm global IR: 0, 15, 30 and 40 min of ischemia followed by 30 min of reperfusion, respectively. Myocardial contractility was determined from left ventricular pressure records (dP/dt, dPmax). Subsarcolemmal mitochondria (SSM) were isolated and analyzed regarding electron transport chain (ETC) coupling using a Clark-type electrode (polarography), membrane polarization (JC1 fluorescence) and Ca2+-handling in terms of Ca2+induced swelling and Ca2+-uptake and release (Ca2+-sensitive electrode).
IR in general depressed LV contractility irrespective of ischemia duration. In contrast, increasing length of ischemia time highly significantly promoted ETC uncoupling at complex I-V and II-IV in state 3 respiration, respectively. Membrane potential showed a distinct hyperpolarization in IR30/30 and IR40/30 compared to the other groups (p < 0.0001), continuously wearing off after CCCP-induced uncoupling. Regarding Ca2+-induced swelling, light transmission of IR40/30 SSMs started to differ significantly (p < 0.04) from IR0/30 after 6.5 min of Ca2+-addition, swiftly followed by IR15/30 (8.5 min) and 30/30 (16.5 min). All effects were delayed by app. 3.6 min by pyruvate addition in parallel assays also halving recorded swellings. Ca2+-uptake revealed slower rates and greater spans in IR15/30 and IR30/30 (p < 0.005) whereas Ca2+-release was delayed for ischemia an duration ≤30 min (p < 0.0001).
Longer ischemia duration in IR injury gradually impairs SSMs in terms of respiratory chain function and Ca2+-homeostasis. Membrane hyperpolarization appears to be responsible for impaired Ca2+-cycling and ETC function. Therefore, ischemia time should be considered an important factor influencing IR experiment-derived conclusions.