Suppression of mitochondrial depolarization of neurons by KCC2 inhibitor VU0463271.

In neurons, massive calcium influx through NMDA receptor causes excitotoxicity by depolarizing mitochondria by opening mitochondrial permeation transition pore (mPTP). Through mPTP, potassium ions (K+) also pass through from the cytosol to mitochondrial matrix, and also causing depolarization. We hypothesized that the K+ concentration gradient between the cytosol and the matrix defines how damage the cells. Potassium chloride cotransporter 2 (KCC2) fundamentally play a role to exclude intracellular chloride ion (Cl-) out in mature neurons by using the driving force of potassium gradient. In this study, we experimentally investigated whether increasing the intracellular K+ concentration by inhibiting this transporter increases the degree of mitochondrial depolarization and the degree of cell death. Exposure of VU0463271, an inhibitor of KCC2 to primary cultured neurons did not change the MTT reducing ability. Contrary to expectations, pre-incubation of VU0463271 did not affect NMDA-induced neuronal cell death. Moreover, pre-incubation of VU0463271 lowered the degree of mitochondrial depolarization, which was induced by NMDA or valinomycin, a mitochondrial uncoupler. It was suggested that the K+ concentration in the cytosol was constantly regulated by buffering by mitochondria.