The influence of external sodium ions on the sodium pump in erythrocytes Available to Purchase

1. A study has been made of the interaction between Na⁺ and K⁺ on the adenosine triphosphatase activity of erythrocyte ‘ghosts’, and on the K⁺ influx and Na⁺ efflux of intact erythrocytes. The adenosine triphosphatase activity and the ion movements were greater at a low external K⁺ concentration in the absence of Na⁺ than they were in the presence of 150mm-Na⁺. The inhibition by external Na⁺ of K⁺ influx had an inhibitory constant of 5–10mm. 2. Activation by K⁺ of kidney microsomal adenosine triphosphatase was retarded by Na⁺, and activation by Na⁺ was retarded by K⁺. Fragmented erythrocyte membranes behaved similarly. 3. These observations suggest that there is competition between Na⁺ and K⁺ at the K⁺-sensitive site of the membrane.