The regulation of mitochondrial movement within muscle cells

Abstract

Mitochondria are dynamic organelles and their movement and morphology are controlled by their interaction with the cytoskeleton. Our purpose was to investigate regulatory events governing mitochondrial movement within muscle cells. Thus, we transfected C2C12 myoblasts with DsRED2‐Mito DNA to visualize mitochondria using realtime imaging. Destabilization of microtubules (MT) using nocodazole reduced organelle velocity and total path length traveled by 72–75%. The amount of time that mitochondria remained stationary increased ~2‐fold when MTs were destabilized. Downregulation of the MT motor protein, Kif5B by siRNA reduced organelle velocity by 33%. Mitochondrial movement was not affected by actin disruption. Thus, the distribution of mitochondria within muscle cells is dependent on a MT‐based transportation system. Using ionomycin to induce an increase in cytoplasmic calcium, we found that organelle velocity was suppressed by 48%, a situation which was reversible upon the chelation of calcium with EGTA. Mitochondrial velocity was also reduced by 22% when cytoplasmic calcium was elevated using thapsigargin, and it returned to basal levels upon the addition of BAPTA‐AM. By understanding mitochondrial movements we can elucidate the underlying basis for organelle interactions, leading to the formation of the mitochondrial reticulum and the distribution of energy in muscle cells. Supported by NSERC.