Mitochondrial Calcium Uniporter Involves in Ischemic Postconditioning Effect through Maintaining Depolarization of Mitochondrial Membrane Potential and Prevents Cell Death Caused by Ischemic Reperfusion Brain Injury in Mouse

Ischemic postconditioning (PostC) phenomenon is known as the neuroprotection against ischemic reperfusion (I/R) injury. One of the key processes in PostC is opening of mitochondrial ATP dependent potassium (mito-K ATP ) channel and depolarization of mitochondrial membrane potential, which triggers the release of calcium ion from mitochondria through the low conductance opening of mitochondrial permeability transition pore (mPTP). Mitochondrial calcium uniporter (MCU) is known as the highly sensitive transporter for uptake of Ca 2+ inwardly existed on the inner mitochondrial membrane. Furthermore, it has attracted attention as a new target of treatments in disease such as neurodegenerative disease, cancer, and ischemic stroke. Thus, we considered that MCU may involve in PostC and trigger its mechanism. In this research, we used the whole-cell patch clamp technique to hippocampal CA1 pyramidal cells from C57BL mice and measured changes in spontaneous excitatory post-synaptic currents (sEPSCs), intracellular Ca 2+ concentration, mitochondrial membrane potential and N-methyl-D-aspartate receptor (NMDAR) currents under the inhibition of MCU by Ruthenium red 265 (Ru265) in PostC. Inhibition of MCU increased sEPSCs occurrence (p = 0.008), NMDAR currents (p < 0.001), intracellular Ca 2+ concentration (p < 0.001) and dead cells (p < 0.001) significantly after reperfusion, indicating the removal of the neuroprotective effects in PostC. Moreover, mitochondrial depolarization in PostC with Ru265 was gradually decreased after reperfusion (p < 0.001). These results suggest that MCU plays an important role in PostC by maintaining mitochondrial depolarization, which suppresses hyperactivation of NMDARs and prevents the elevation of intracellular Ca 2+ concentration against I/R injury.