MICROPUNCTURE AND MICROPERFUSION STUDY OF L-GLUCOSE SECRETION IN RAT KIDNEY

Studies with the free flow micropuncture technique have shown that the ratio of TF/Pl-glucose to TF/PInulin in proximal tubular fluid, in distal tubular fluid, and in more than half of the final urine samples measured was greater than one, which suggests that l-glucose was actively secreted. Studies with the microperfusion technique confirmed this finding and showed that l-glucose was secreted by the proximal tubules. A maximum rate of secretion was reached at a plasma concentration of 4 mM. The tubular secretion of l-glucose was augmented by the presence of 16.6 mM d-glucose in tubular lumen and inhibited by 10-4 M phlorizin. Kinetic analysis showed that the Vmax values for l-glucose secretion in the absence and in the presence of d-glucose are 5.0×10-10 and 6.3×10-10 mol×cm-2×sec-1 respectively which were very close to the value reported for the Vmax for d-glucose reabsorption. However, the Km for l-glucose secretion was 3.1 mM and was reduced to 1.6 mM when d-glucose was present in the perfusion fluid. The Km for d-glucose reabsorption has been reported to be 0.6 mM (8). The results of this investigation were interpreted as being consistant with the hypothesis that l-glucose secretion and d-glucose reabsorption share the same carrier system. © 1969 Springer-Verlag.