Membrane potentials and sugar transport by ATP-depleted intestinal cells: effect of anion gradients

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Abstract
Rotenone or dinitrophenol treatment was used to decrease cellular ATP levels in isolated chicken intestinal epithelial cells by over 90% and to produce a cell population in which no steady-state accumulation of 3-O-methylglucose (3-OMG) against a concentration gradient is observed. In the presence of imposed inward-directed Na-anion gradients, these cells accumulate 3-OMG against a concentration gradient. The degree of maximal 3-OMG accumulation and initial influx stimulation in the presence of a given anion or combined Na-anion gradient can be correlated with the magnitude of the diffusion potential as determined by the membrane permeability of the given anion (SCN- > Cl- > isethionate- > SO42-). 3-OMG influx in the presence of a large NaCl gradient is comparable in ATP-depleted and normally energized cells. The slight difference in influx (energized > ATP depleted) is diminished by ouabain, suggesting that energized cells maintain a larger membrane potential (diffusion potential or rheogenic Na+-K+-ATPase ion pump-generated potential) than the ATP-depleted cells. Although initial rates of 3-OMG uptake into Na+-depleted normally energized cells also varies with the anion gradient, these differences disappear with time of incubation in Na+ or when cells are preincubated in Na+. In this situation, function of a rheogenic Na+ pump can establish a membrane potential in contrast to the case with ATP-depleted cells, which have a potential only as long as imposed ion gradients are maintained. All these experiments point to an important role for the electrical membrane potential as a driving force for Na+-dependent solute transport systems in both ATP-depleted and normally energized cells.

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