Effect of dietary and extracellular potassium on lysine metabolism in the rat

Abstract

Previous studies have shown that potassium (K) depletion leads to the accumulation of lysine and other cationic amino acids in tissues. The metabolic nature of this interaction is unknown but is presumably related in part to a unique aspect of these amino acids, possibly their charge. These studies were completed to evaluate the nature of the effect of K on lysine metabolism in the rat. In the first study, 42 rats were maintained on K-deficient or K-adequate diets for 10 days, after which blood and tissue samples were taken from 12 rats for electrolyte, amino acid and blood gas analyses. Tissue slices of liver, kidney and segments of diaphragm were prepared from the remaining 30 rats (15 per group) and incubated in medium containing either 3 or 6 mM K, and effects of dietary and medium K concentrations on lysine catabolism were determined. In the second study, the effects of 0, 3, 6 or 12 mM K on 14C-lysine uptake, catabolism and incorporation into protein were evaluated. Dietary K deficiency did not influence blood pH, bicarbonate concentration or base excess of blood; however, it decreased the concentration of plasma K and caused accumulation of lysine and arginine in muscle and lysine in liver. K deficiency resulted in a 36% reduction in the rate of lysine catabolism in kidney. Much of the dietary K effect may be related to diminished plasma K concentration, as low K concentration in vitro caused similar, although less dramatic, decreases in lysine oxidation, diminished incorporation of lysine into protein in kidney and increased lysine uptake in both liver and kidney. K deficiency appears to conserve lysine in the free form in the intracellular pool by enhancing cellular uptake and by decreasing the degradation of lysine and the utilization of lysine in protein synthesis.