AMINO-ACID STIMULATION OF NA,K-ATPASE ACTIVITY IN RAT PROXIMAL TUBULE AFTER HIGH-PROTEIN DIET

Ouabain-sensitive (OS) O2 consumption was determined in proximal tubular cells from weanling rats fed 21% (normal-protein, NP) or 50% (high-protein, HP) protein diet for 4 days. Butyric acid 10-3 M was added as a substrate for mitochondrial respiration and the ionophore amphotericin B (10 μg ml-1) was used to sodium-load the cells. OS respiration was higher in HP than in NP cells in both DME and amino acid-free electrolyte solution (ES). Amphotericin B significantly increased OS respiration in both NP and HP cells, implying that the Na-K pump was activated by increased intracellular Na. In cells incubated in ES, addition of amio acids stimulated OS respiration significantly in HP cells (16.9 ± 1.4 vs 21.2 ± 1.1 nmol min-1 mg-1 protein) and in NP cells (13.9 ± 0.3 vs 14.9 ± 0.6 nmol min-1 mg-1 protein). Stimulation was significantly higher in HP cells (26 ± 4%) than in NP cells (7 ± 4%) (P < 0.001). The amino acids did not stimulate ouabain-insensitive respiration. The results indicate that an HP diet to weanling rats will increase proximal tubule cell Na,K-ATPase-dependent respiration by enhancing Na entry via the Na-amino acid symports.