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Publisher Summary: This chapter reviews the mechanism of renal sugar transport at the subcellular level and discusses the present knowledge of the molecular mechanism of sugar transfer across the epithelial plasma membranes in the proximal tubule of the kidney. The brush border membrane of the proximal tubule epithelial cell has been shown to contain a stereospecific sugar transport system that is inhibited competitively by phlorizin and whose affinity is increased by the presence of sodium ions. The transport system, in addition, is capable of accumulating sugars across the brush border membrane, provided there exists an electrochemical potential difference for sodium. This indicates that at the cellular level D-glucose entry across the luminal cell membrane is coupled to a symport of sodium and that the energy for intracellular accumulation and transepithelial sugar transport is derived from the electrochemical potential difference for sodium between the intra- and extracellular fluids. The transfer of sugars across the basal-lateral plasma membranes is also facilitated by transport systems, which, however, lack sodium sensitivity and sodium-dependent accumulation. Also, their sensitivity to phlorizin is much lower than the sensitivity of the transport system located in the brush border.
