Abstract
1. Potassium-depleted muscles have been analysed for cations, phosphocreatine, adenosine triphosphate and lactate before or after an exposure to a medium with 10 mM potassium salt.2. The net movements of sodium out and potassium in when the system is anaerobic but not otherwise poisoned are accompanied by break-down of phosphocreatine and formation of lactate.3. In bicarbonate media oligomycin has little perceptible effect upon these observed changes, which is taken to indicate that mitochondrial phosphorylation is not essential. An inhibition by oligomycin was noted in media buffered with Tris.4. Dinitrofluorobenzene, which poisons creatine phosphotransferase, leads to the cation changes being accompanied by break-down of ATP and formation of lactate. This indicates that ATP is more directly concerned with energizing the ion movements than is phosphocreatine.5. Iodoacetate inhibits the glycolytic process and the ion movement is then accompanied by more phosphocreatine break-down than in the other conditions; the level of ATP also falls.6. The mean number of sodium ions moved out is closely equal to the number of potassium ions moved in. Conditions mentioned in (2) and (3) above lead to about 2.5 sodium ions being moved out per high-energy phosphate bond hydrolysed provided allowance is made for the glycolytic resynthesis of ATP.7. Some measurements of membrane potential under comparable conditions of ion movement are reported and these are used to calculate the energy requirement of the process of sodium-potassium interchange.