Intracellular ion concentrations of epithelial cells in rat small intestine. Effects of external potassium ions and uphill transports of glucose and glycine.

The water content (V) and the concentrations of K+, Na+, and Cl- in the epithelial cells of rat small intestine ([K]i, [Na]i, and [Cl]i) were were measured in high K+ media and in the presence of glucose or glycine (20 mM). Raised external K+ concentrations brought about increases in V. Parallel with swelling of the cell, increases in [K]i and [Cl]i and decreases in [Na]i were observed. Such a pattern of changes in [K]i, [Na]i, and [Cl]i was concordant with that expected from the K+ -induced depolarization and the permeability properties of the cell membranes. In the presence of D-glucose or glycine, remarkable increases in V were observed, which resulted in concomitant decreases in [K]i, [Na]i, and [Cl]i. Assuming the osmotic balalance between intra- and extracellular fluids, the concentrations of accumulated solutes within the cell as well as the net gain of these ions were estimated. The results demonstrated that the accumulated solute was in an osmotically active form, resulting in cell swelling with concomitant decreases in [Cl]i, while the net gain of Na+ and K+ in the cells occurred despite apparent decreases in [Na]i and [K]i.