Relation of the metabolism of pigeon-muscle mitochondria to the net uptake of potassium and its selection over sodium

Three processes (cation accumulation, rate of oxidation, and rate of phosphorylation) were measured on each of the mitochondrial preparations made from pigeon-breast muscle. Mitochondria were incubated for 30 minutes in media containing ATP, a hexokinase–glucose acceptor system, and sodium and potassium in the ratio of 1:1. Variation in metabolic rate was achieved by using α-ketoglutarate, α-ketoglutarate + muscle supernatant, malate, or β-hydroxy-butyrate as substrates. The mitochondria and the media were analyzed before and after incubation so that accurate concentration gradients could be calculated. When α-ketoglutarate was substrate, a small but highly significant net uptake of potassium and an increased potassium gradient were found. The change in sodium was statistically insignificant, showing selection of potassium over sodium. Only in β-hydroxybutyrate, where the rates of respiration and phosphorylation were low, was there a net uptake of sodium as well as potassium so that no cation selection was apparent.