Passage of glucose through the cell membrane of capillary endothelium

The mechanisms of glucose passage through the cell membrane of vascular endothelium were studied in vitro with a preparation of pure blood capillaries isolated from the rete mirabile of the eel swimbladder. In countertransport experiments, no competition for a common carrier could be detected between D-glucose and 3-O-methylglucose or between D-glucose and L-glucose. In the endothelial cells, inward and outward fluxes of labeled sugars were not changed when studied against concentration gradients of corresponding unlabeled sugars. The distribution of 3-O-methylglucose-14C and L-glucose-14C at equilibrium between intracellular and extracellular water was not modified by reducing their specific activity in the medium over a wide range. The addition to the medium of phlorizin 10-5 or 10-7 M, 3-O-methylglucose 60 mM, or L-glucose 60 mM did not reduce the rate of glucose utilization by the capillary tissue. The temperature coefficient for glucose uptake between 27 and 37 degrees C averaged 1.4. Insulin had no effect on the initial rate of 3-O-methylglucose-14C entry into cellular water. It is concluded that in the eel capillaries the mechanism of glucose passage into the vascular endothelial cell is compatible with the kinetics of free diffusion.