Tubular extrusion of D-glucose in the isolated rabbit kidney perfused in vitro.

The extrusion mechanism of d-glucose by tubular cells was investigated in isolated rabbit kidneys perfused with normal or hyperglicemic blood, added with 14C-inulin, by relating the values of the ratio between the intracellular and extracellular glucose concentration (Gi/Ge) in the cortical tissue to the respective plasma concentration Gp (= Ge). The apparent extracellular space was calculated in each experiment from the kinetics of the 14C-inulin efflux from cortical slices excised at the end of the perfusion period (mean value = 20.7 +/- 1.7 of the total vol.). The total intra and extracellular amount of glucose was measured in two contiguous slices excised from the cortex. The total water was expressed by the difference between the fresh and dry weight of the slice, the intracellular water by the difference between the total and extracellular water. From these volumes the respective apparent glucose concentrations could be found. The Gi/Ge values tend to 1, that is to a uniform intra and extracellular distribution of glucose, only at high plasma glucose levels. These results do not seem to be in agreement with a D-glucose transfer from the cell to the subepithelial spaces down a concentration gradient.