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 ofl-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 ford-glucose reabsorption. However, the Km forl-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