Fig. 6. Imaging of mitochondria in permeabilized myocardial fibers by the membrane-potential-sensitive probe teramethylrhodamine ethyl ether (TMRE). (A) Fibers in the presence of 2mmoll^-1 ATP, 2mmoll^-1 malate and 5mmoll^-1 glutamate (concentration of free Ca²⁺ in Ca-EGTA buffer: 0.1 µmoll^-1). (B) The same fibers after addition of calcium chloride (final concentration of free Ca²⁺ in Ca-EGTA buffer: 1.0 µmoll^-1). The left fiber in a flexiperm chamber was not fixed, while the right (longer) fiber was fixed by its ends. In A, both fibers are relaxed. In B, the left fiber is contracted, while the right fiber, which is contracting almost isometrically, shows significant structural changes due to sarcomere contraction. Note the empty spaces between mitochondria.