Glucose transport in isolated perfused proximal tubules of snake kidney

Glucose transport was studied in isolated, perfused snake (Thamnophis spp.) renal tubules. When 14C-labeled and unlabeled glucose concentrations for bath and perfusate were identical, net transepithelial glucose transport occurred from lumen to bath. Maximum rates of transport were 1.24 X 10-12 and 2.17 X 10-12 mol min-1 mm-1 in proximal-proximal and distal-proximal segments, respecitvely. Glucose concentration in cells of perfused tubules of both segments was less than that of bath and lumen when tubules spontaneously stopped transporting glucose. Transepithelial glucose permeability ath leads to lumen) was about 0.25 X 10-5 cm sec-1 for both segments. Peritubular membrane permeability (bath leads to cell) was about 0.50 X 10-5 cm sec-1 for both segments. Luminal membrane permeabilities (cell leads to lumen) were 0.29 X 10-5 and 0.65 X 10-5 cm sec-1 for proximal-proximal and distal-proximal segments, respectively. Luminal membrane permeability in opposite direction (lumen leads to cell) was about 10.0 X 10-5 cm sec-1 for both segments. These results indicate that, during maximum glucose absorption, glucose enters cells down concentration gradient across luminal membrane by a mediated process and is transported out of the cells against concentration gradient at peritubular membrane.