[Quantitative relationship between the monosaccharide induced change in ion transport and the monosaccharide...

1. In the rat's jejunum, the changes induced by Na+-dependently transported monosaccharides (10 mM) of the unidirectional Na+- and K+-influx across the microvilli membrane were studied under varying metabolic conditions. 2. The monosaccharide induced change of Na+- and K+-influx is a function of the ion gradients active across the microvilli membrane. 3. In the in vitro preparation during the process of energy-dependent accumulation the monosaccharide induced change of permeability in the microvilli membrane decreases the K+ concentration, while the Na+ concentration increases. 4. The monosaccharide concentration in the tissue reaches a final value which is proportional to the change of Na+- and K+-influx and to the change in ion concentrations, and which is retained even upon compensation of the gradient and at low intracellular K+ concentrations. 5. The correlation between the breakdown of the ion gradient and the rise of monosaccharide accumulation is explained by the monosaccharide induced restriction of the active ion transport and the ensuing change of energy dissipation in favour of the monosaccharide transport. The (Na+ + K+)-ATPase in the microvilli membrane is discussed as being transmitter of the energy from the ion gradients.