Respiration of mitochondria of red and white skeletal muscle

¹ Department of Physiology, University of Manitoba, and St. Boniface General Hospital, Winnipeg, Canada

Mitochondria of guinea pig red and white skeletal muscle were isolated in a medium containing 0.25 m sucrose, 1 mm ethylenediamine tetraacetate, and 1% fraction V bovine albumin. Oxidative phosphorylation with pyruvate-malate as substrate was tightly coupled in both types of mitochondria when oxygen uptake was measured over a 2- to 4-min period with a platinum electrode. The P/O ratios approached the theoretical value of 3. Oxygen consumption was also determined manometrically with the substrates 10 mm pyruvate—1 mm malate, 10 mm succinate, 6 mm reduced nicotinamide adenine dinucleotide (NADH₂), 20 mm dl-lactate, and 12–20 mm dl--glycerophosphate. White muscle mitochondria had a higher rate of oxygen consumption with -glycerophosphate than with lactate, succinate, and NADH₂. Those of red muscle were less active with -glycerophosphate than with the other substrates. These results indicate that an -glycerophosphate shuttle may couple the reactions generating NADH₂ in the cytoplasm of white muscle with the mitochondrial respiratory chain. The properties of the red muscle mitochondria suggest that the direct oxidation of NADH₂ may be more important in this tissue than the -glycerophosphate shuttle.

Key Words: oxidative phosphorylation • -glycerophosphate shuttle • nicotinamide adenine dinucleotide • oxygen consumption • muscle mitochondria

Submitted on July 8, 1963