Identification of mitochondria by osmotic swelling and tetrazolium staining

¹ Department of Physiology, University of North Carolina Medical School, Chapel Hill, North Carolina

When tissue homogenates were diluted in sucrose solutions of decreasing concentration or in distilled water, there was a graded resistance of the mitochondria to osmotic swelling, and even in distilled water some granules having the electron microscopic appearance of mitochondria did not swell. After pretreatment with distilled water, mitochondria incubated at 37°C in the presence of iodophenyl tetrazolium and succinate showed distinct formazan granules within the swollen mitochondria. There was satisfactory agreement between mitochondrial counts based on osmotic swelling in distilled water and on staining with tetrazolium.