Significance of sodium ions in active intestinal transport of nonelectrolytes

The active transport of 3-O-methylglucose, l-tyrosine, dl-phenylalanine, and uracil was studied in the surviving isolated frog small intestine suspended in Ringer's solution of varying ionic compositions. The rate of active transport of each nonelectrolyte was significantly reduced if Li or K was substituted for Na as the principal cation in the nutrient medium surrounding both surfaces of the intestine.