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Sodium-alanine cotransport in renal proximal tubule cells investigated by whole-cell current recording

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Hoyer,  Joachim
Department of Physiology, Max Planck Institute of Biophysics, Max Planck Society;

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Gögelein,  Heinz
Department of Physiology, Max Planck Institute of Biophysics, Max Planck Society;

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Citation

Hoyer, J., & Gögelein, H. (1991). Sodium-alanine cotransport in renal proximal tubule cells investigated by whole-cell current recording. Journal of General Physiology, 97(5), 1073-1094. doi:10.1085/jgp.97.5.1073.


Cite as: https://hdl.handle.net/21.11116/0000-0008-32FA-6
Abstract
Sodium-alanine cotransport was investigated in single isolated proximal tubule cells from rabbit kidney with the whole-cell current recording technique. Addition of L-alanine at the extracellular side induced an inward-directed sodium current and a cell depolarization. The sodium-alanine cotransport current was stereospecific and sodium dependent. Competition experiments suggested a common cotransport system for L-alanine and L-phenylalanine. Sodium-alanine cotransport current followed simple Michaelis-Menten kinetics, with an apparent Km of 6.6 mM alanine and 11.6 mM sodium and a maximal cotransport current of 0.98 pA/pF at -60 mV clamp potential. Hill plots of cotransport current suggested a potential-independent coupling ratio of one sodium and one alanine. The apparent Km for sodium and the maximal cotransport current were potential dependent, whereas the apparent Km for L-alanine was not affected by transmembrane potential. The increase in Km for alanine with decreasing inward-directed sodium gradients suggested a simultaneous transport mechanism. These results are consistent with a cotransport model with potential-dependent binding or unbinding of sodium (high-field access channel) and a potential-dependent translocation step.