The connexion between the ion-binding sites of the sodium pump

• Published in: The Journal of physiology Vol. 260; no. 2; pp. 371 - 385
• Main Authors: Chipperfield, A R, Whittam, R
• Format: Journal Article
• Language: English
• Published: England The Physiological Society 01-09-1976
• Subjects: Binding Sites; Biological Transport, Active; Erythrocytes - metabolism; Humans; Kinetics; Potassium - blood; Sodium - blood
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.1976.sp011520

1. A study has been made of K influx into human red blood cells in order to determine the influence of internal Na on the
affinity of the Na pump for external K. Cells were prepared to contain minimal K and two Na concentrations (about 10 and 30
mueqiv/ml. cells) and incubated in solutions with a range of K concentrations. 2. In choline (Na-free) Ringer, activation
of K influx by external K was hyperbolic. The Km for external K increased as the internal Na concentration was raised. The
increase was greater than the increase in K influx with saturating external K. The Km for external K increased towards a limiting
value as the internal Na concentration was raised. 3. In contrast, in Na-Ringer, the activation by external K was sigmoidal
and the affinity for external K was independent of the internal Na concentration. 4. K influx was measured at two submaximal
levels of external K with a range of internal Na. The affinity for internal Na fell as external K was raised. 5. The results
suggest that in the absence of competition between Na and K on the same side of the membrane, there is a connexion between
the ion-binding sites of the Na pump.