Induction of Na?K-ATPase in plasma membranes of rat cecum mucosa by diet: Time course and kinetics

Abstract

Dietary polyethylene glycol (PEG) induces an increase in the specific activity of Na⁺−K⁺-activated adenosine triphosphatase (Na−K-ATPase) in the cecum mucosa of rats. Using cecum mucosa homogenates and cellular subfractions obtained by differential centrifugation, the induction process was studied with respect to time course, subcellular distribution and properties of the enzyme. In comparison with controls, Na−K-ATPase specific activity was stimulated in PEG treated rats in the total homogenate and the microsomal (105000×g) but not in the mitochondrial (9000×g) or nuclear (1000×g) sediment. The specific activity of Mg-ATPase did not change in any of the fractions. Na−K-ATPase induction was statistically significant after 2 days and complete after 1–2 weeks, in parallel with the previously described stimulation in net sodium absorption. Kinetic analysis showedV _max for ATP to be doubled while K_m for ATP, Na and K as well as the optimal Mg/ATP ratio and K_i for ouabain remained unchanged. It is proposed that Na−K-ATPase and active sodium transport are closely associated in rat cecum and that dietary Na−K-ATPase stimulation is due to the induction of more enzyme molecules per unit basolateral cell membrane.