Coupling of aerobic glycolysis and Na⁺-K⁺-ATPase in renal cell line MDCK

The relation between the activity of the Na⁺-K⁺-ATPase and the metabolic source of ATP was investigated in suspensions of MDCK cells. The pump activity of Na⁺-K⁺-ATPase was estimated from the initial rate of ouabain-sensitive K⁺ uptake into K⁺-depleted cells. Uptake was initiated by the reintroduction of K⁺ to the medium in which the cells were suspended. The metabolic source of ATP was varied by changing the substrates supplied to the suspension. Cells respiring on glutamine produced ATP from oxidative metabolism alone, whereas cells incubated with glucose and glutamine produced ATP via glycolysis and oxidative phosphorylation. Over a wide range of extracellular K⁺ concentrations, the initial rate of K⁺ uptake was faster in cells incubated with glucose and glutamine when compared with cells incubated with glutamine alone. Kinetic analysis together with ouabain-binding data demonstrated that this increase in K⁺ uptake was due to an increase in maximal velocity (V(max)) at a constant number of Na⁺-K⁺-ATPase transport sites. In addition, steady-state studies revealed that the addition of glucose to K⁺-depleted cells respiring on glutamine alone resulted in a net ouabain-sensitive influx of K⁺. These data demonstrate that in MDCK cells the maximal capacity for transport via the Na⁺-K⁺-ATPase is greater when ATP is produced from both glycolysis and oxidative phosphorylation than when ATP is produced from oxidative phosphorylation alone. Arguments are presented that suggest this increase in pump activity with glucose is not related to changes in the cytosolic concentration of ATP but is more likely due to specific interactions between glycolysis and Na⁺-K⁺-ATPase activity.