Glucose transport in isolated perfused proximal tubules of snake kidney
Barfuss, D.W.; Dantzler, W.H.
American Journal of Physiology 231(6): 1716-1728
1976
ISSN/ISBN: 0002-9513 PMID: 990110 Document Number: 98357
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 .times. 10-12 and 2.17 .times. 10-12 mol min-1 mm-1 in proximal-proximal and distal-proximal segments, respectively. Glucose concentration in cells of perfused tubules of both segments was less than that of bath or lumen during maximum glucose absorption. This cellular glucose concentration increased to that of bath and lumen when tubules spontaneously stopped transporting glucose. Transepithelial glucose permeability (bath .fwdarw. lumen) was about 0.25 .times. 10-5 cm s-1 for both segments. Peritubular membrane permeability (bath .fwdarw. cell) was about 0.50 .times. 10-5 cm s-1 for both segments. Luminal membrane permeabilities (cell .fwdarw. lumen) were 0.29 .times. 10-5 and 0.65 .times. 10-5 cm s-1 for proximal-proximal and distal-proximal segments, respectively. Luminal membrane permeability in posite direction (lumen .fwdarw. cell) was about 10.0 .times. 10-5 cm s-1 for both segments. During maximum glucose absorption, glucose probably enters cells down concentration gradient across luminal membrane by a mediated process and is transported out of the cells against concentration gradient at the peritubular membrane.