Energy metabolism of renal cell lines, A6 and MDCK: Regulation by Na-K-ATPase

The energy metabolism of two continuous cell lines of renal origin, MDCK (Madin-Darby dog kidney) and A6 (toad kidney), was investigated by measuring the oxygen consumption (QO₂) and lactate production (J(lac)) by cells taken into suspension from monolayer cultures. Cells suspended from fully differentiated monolayers produce ~80% of their ATP requirements from oxidative metabolism. The interrelationship between ion transport and metabolism was determined by analyzing the ouabain sensitive components of intermediary metabolism under control conditions and after the stimulation of active Na-K transport with nystatin. In both cell lines, ~25% of the net rate of ATP production was inhibited by ouabain. Ouabain inhibited J(lac) by 40% in MDCK and 45% in A6 cells, whereas QO₂ was decreased by only 20% in both cell lines. In the presence of 0.05 mg nystatin/mg cell protein, ouabain sensitive J(lac) increased by 75% in MDCK and was more than doubled in A6, whereas the ouabain-sensitive QO₂ was not statistically different than control. This preferential stimulation of glycolysis with nystatin was not due to a limited capacity of mitochondrial oxidative phosphorylation since nystatin treatment of cells incubated without glucose (no glycolysis) significantly elevated the rate of QO₂. These data demonstrate that aerobic glycolysis is more sensitive than is QO₂ to changes in hydrolytic activity of the Na-K-adenosine triphosphatase (ATPase), in both cell lines.