Microtubule Disorganization Affects the Mitochondrial Permeability Transition Pore in Cardiac Myocytes

Background: Microtubule (MT) disorganization is related to cardiac disorders. To elucidate the mechanism by which disorganization of the MT network deteriorates cardiac function, the relationship between MT disorganization and mitochondrial permeability transition pore (mPTP) in cardiac myocytes was investigated. Methods and Results: The effects of MT stabilization (by paclitaxel) and MT disruption (by nocodazole) on mitochondrial membrane potential (Delta psi m) and the opening of mPTP were measured in permeabilized Sprague-Dawley rat myocytes. Both paclitaxel and nocodazole depolarized Delta psi m and opened mPTP. When isolated mitochondria were exposed to paclitaxel or nocodazole, there were no changes in Delta psi m. The effects of paclitaxel or nocodazole on Delta psi m depolarization and mPTP were inhibited by cyclosporin A. Treatment of myocytes with 0Ca+BAPTA or inhibition of sarcoplasmic reticulum (SR) Ca2+ uptake by thapsigargin prevented the effect of paclitaxel on mPTP, but not that of nocodazole. Inhibition of the mitochondrial Ca2+ uniporter by Ru360 did not alter the effect of paclitaxel on mPTP. Paclitaxel reduced the expression of the mitochondrial fusion protein, mitofusin-2, and induced mitochondrial fragmentation. Conclusions: Disruption of the MT network by nocodazole might destroy the MT-mitochondria connection and alter mitochondrial function. MT disorganization by paclitaxel could regulate mPTP through the outer mitochondrial membrane complex and the Ca2+-sensitive signaling pathway, which also interacts with the mitochondrial fusion protein, mitofusin-2.