Kinetic evaluation of the Na-K pump reaction mechanism

• Published in: The Journal of physiology Vol. 273; no. 2; pp. 489 - 514
• Main Author: Sachs, J R
• Format: Journal Article
• Language: English
• Published: England The Physiological Society 01-12-1977
• Subjects: Biological Transport, Active; Cell Membrane - metabolism; Erythrocytes - metabolism; Extracellular Space - metabolism; Humans; Intracellular Fluid - metabolism; Kinetics; Models, Biological; Potassium - blood; Potassium - metabolism; Sodium - blood; Sodium - metabolism
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.1977.sp012106

1. The ouabain-sensitive K influx was measured at varying external K concentrations ([K]o) and at several fixed internal Na
concentrations ([Na]c). The cells were nominally K-free and the solutions Na-free. Both the apparent maximal velocity (VM)
and the apparent Michaelis constant for K (KK) increased as Nac increased. The ratio app. VM/app. KK increased with increasing
Nac. 2. The ouabain-sensitive Cs influx was measured at varying external Cs concentrations and at several fixed Nac in K-free
cells and Na-free solutions. Both app. VM and app. Kcs increased as Nac increased and the ratio app. VM/app. Kcs increased
with increasing Nac. 3. The data were evaluated in terms of ping-pong model and a simultaneous model for the pump reaction
mechanism. The simultaneous model described the data adequately and the ping-pong models did not. 4. The K influx was measured
at varying external K concentrations in solutions containing Na and at a low and high Nac; the cells contained K. The relation
between the pump rate and the external K concentration was sigmoid. A Hill equation was fitted to the data. KK was higher
in the high Nac cells, but the Hill coefficient (n) was not altered as Nac increased. 5. The K influx was measured at varying
internal Na concentrations and two fixed external K concentrations; the cells contained K. The relation between the pump rate
and Nac was sigmoid. When a Hill equation was fitted to the data, it was found that KNac was higher at the high external K
concentration, but n was the same at both K concentrations.