Active transport of glycine by mouse pancreas Evidence against the Na + gradient hypothesis

Abstract

The mouse pancreas when incubated in vitro does not maintain a large Na + gradient. Despite the near absence of a Na + gradient, accumulation of glycine against its concentration gradient is appreciable being 10–12 times that of the medium with 2 mM extracellular glycine. Ouabain, at concentrations less than 0.5 mM, causes a greater perturbation of the steady-state accumulation of glycine than of Na + or K + distribution. Extracellular Na + increases the v max of glycine uptake without a significant effect on the K m . The extent of glycine uptake can be correlated with the level of cellular ATP and extracellular Na + but not with the magnitude of the Na + and/or K + gradients. The initial rate of glycine uptake is directly proportional to the extracellular Na + concentration.