Electrical coupling and plasticity of the mitochondrial network

Abstract

Kinetic fluorescence imaging and the potentiometric probe tetramethylrhodamine methyl ester (TMRM) were used to evoke and detect changes in membrane potential (δ Ψm) of individual mitochondria in living cells. As a combined effect of preferential TMRM accumulation in mitochondria, and of TMRM photoactivation, individual organelles displayed sharp transient depolarizations caused by local reactive oxygen species (ROS)-mediated gatings of the mitochondrial permeability transition pore (PTP). In COS-7 cells, such directed repetitive gatings of the PTP gave rise to stochastic δ Ψmflickering at the level of individual organelles, but also to prominent synchronous δ Ψmtransitions in whole subgroups of the mitochondrial population, indicative of the existence of an underlying electrically coupled mitochondrial network. In single cells, this network could comprise as much as 65% of the total mitochondrial population, a nd exhibited a high plasticity with mitochondrial units spontaneously connecting to and disconnecting from the coupled structure within seconds. These results indicate that in resting cells, the mitochondrial network is a dynamic proton-conducting struct ure capable to commute and coordinate electrical signals generated by the PTP.