Fig. 1. Change of mitochondrial morphology during swelling. Mitochondria within a HeLa cell were stained by Mitotracker and imaged using a fluorescence microscope. (A) Under the normal condition, mitochondria appeared as filamentous structures. (B) After mitochondria were induced to swell by exposing the cell to a hypo-osmotic medium (5 mM potassium phosphate buffer, pH 7.4) for 1 minute, mitochondria were found to change into spherical shapes. (C) Calculated changes in volume and diameter when a mitochondrion swelled without stretching its surface. The length/diameter ratio was assumed to be five before swelling (Scheffler, 1999). Scale bar: 10 µm.