Steady-state physiological variations across a graded series of Na,K-ATPase-amplified cells

Measurements of internal ion concentrations, amino acid pools, and membrane potential were made across a series of HeLa subclones which are amplified for the genes for the sodium- and potassium-activated ATPase (Na,K-ATPase). These subclones expressed heterogeneous levels of ouabain-binding sites, allowing us to construct a graded amplification series. While [K+]i levels did not vary systematically across the series studied, [Na+]i ranged from 9 to 20 mM as a function of Na,K-ATPase expression. Steady-state accumulation of tetraphenylphosphonium in low versus high potassium was used to measure membrane potential. Values for [Na+]i and the membrane potential were used to calculate the sodium electrochemical potential, which was also found to be a function of Na,K-ATPase expression. Measurements of acid-soluble amino acid pools in cell lysates demonstrated that amino acids which are substrates for sodium-dependent transport systems, or which can potentially exchange through system L for a substrate of a sodium-dependent system, varied as a function of the sodium electrochemical potential. This confirmed our prediction of increased amino acid pool sizes in Na,K-ATPase-amplified lines based on observations of elevated flux through the sodium-independent system L. Finally, we measured lactate production and glycolytic potential in a subset of clones and found that both were reduced in subclones with elevated Na,K-ATPase.