The role of brush border enzymes in tubular reabsorption of disaccharides

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Abstract
Renal tubular reabsorption of maltose, sucose and lactose were studied in vivo et situ by continuous microperfusion of single proximal convolutions of rat kidney. The14C-label of maltose (2.5 mmol/l) was removed from the lumen of the proximal tubule at about the same rate as found for glucose. Maltose reabsorption was completely inhibited in presence of 30 mmol/l glucose or of 0.1 mmol/l phlorizin. Chemical analysis of the samples showed a complete conversion of maltose into glucose within a perfusion distance of 2 mm. It is concluded from these results that within the tubular lumen maltose is split very rapidly by a brush border glucosidase. The short half time of this process permits the breakdown product glucose to be almost completely reabsorbed subsequently within the proximal tubule. In contrast, sucrose and lactose were neither split nor reabsorbed by the tubule brush border.