(19) VISUALIZATION OF CYCLICAL MITOCHONDRIAL DEPOLARIZATIONS IN CELL CULTURE

C.P. Fall* and J.P. Bennett, Jr.
University of Virginia Health Sciences Center
(* Current affiliation: Univ. of CA, Davis)

Mitochondria not only facilitate chemiosmotic energy transduction, but also are excitable organelles that are important participants in intracellular Ca+2 signaling and are obligate participants in the active cell death cascade known as apoptosis. Underlying these functions is the cyclosporin A (CSA) sensitive mitochondrial permeability transition pore (MTP), which can open transiently in a low conductance mode (MTPL) to relieve excess electrochemical potential or Ca+2, and opens irreversibly during the initiation of apoptosis. Here we image transient mitochondrial depolarizations and repolarizations in cultures of the SH-SY5Y human neuroblastoma cell. These depolarizations are CSA sensitive, they are blocked by chelating cytosolic Ca+2 or depolarizing mitochondria with FCCP, and they involve all visualized mitochondria within individual cells. Our data reinforce the notion that mitochondria are excitable organelles and suggest that networks of mitochondria can constitute an excitable system that may use Ca+2 as a diffusible messenger to recruit neighboring mitochondria to depolarize.