The effect of alkali metal ions on sugar transport in muscle: Interaction with the sugar carrier or indirect: Effect

Abstract

1. 1. Membrane transport of sugar in “intact” rat hemidiaphragm in vitro was studied by measuring fluxes of 3-O- methyl- d-[ 14C ] glucose in and out of the intracellular water. 2. 2. The stimulation of influx in a K +-free medium, demonstrated earlier, was correlated with the duration of exposure to K +-free medium and persisted for some time after transfer of tissue to a normal medium. The time course of this effect was parallel to that of concomitant changes in intracellular Na + and K + levels due to inhibition of the Na + pump. 3. 3. Efflux of sugar from the tissue was stimulated under all conditions which stimulated influx. The effect of K +-free medium also showed the same gradual onset and persistence after transfer of the tissue to normal medium. 4. 4. These effects are not consistent with transport regulation through binding or co-transport of K + on the sugar carrier, nor do they support a direct link between sugar transport and the activity of the Na + pump as such. The data suggest that the increased Na + or decreased K + level in the cell, or both, caused by Na + pump inhibition, enhances sugar transport in and out of the cell to an equal extent.