ABSENCE OF A TRANSCELLULAR OXALATE TRANSPORT MECHANISM IN LLC-PK1 ANDMDCK CELLS CULTURED ON POROUS SUPPORTS

Transepithelial oxalate transport across polarized monolayers of LLC-P K1 cells, grown on collagen-coated microporous membranes in Transwell culture chambers, was studied in double-label experiments using [C-14] -oxalate together with [H-3]-D-mannitol as an extracellular marker. Th e [14(C)]-labeled glucose analog alpha-methyl-glucoside (alpha-MG) was used as functional marker for active proximal tubular sugar transport . Cellular uptake of oxalate and alpha-MG at both the apical and basol ateral plasma membrane was determined. When added to the upper compart ment, alpha-MG was actively taken up at the apical membrane, directed through the cells to the basolateral membrane and transported to the l ower compartment, indicating functional epithelial sugar transport by LLC-PK1 cells. In LLC-PK1 cells, the uptake of alpha-MG at the apical membrane was approximately 50 times higher than that at the basolatera l membrane. In contrast to this active transport of sugar, LLC-PK1 cel ls did not demonstrate oxalate uptake either at the apical or basolate ral plasma membrane. The apical-to-basolateral (A- > B) flux of oxalat e in LLC-PK1 cells was identical to the basolateral-to-apical (B- > A) oxalate flux in these cells. Moreover these flux characteristics were similar to those found for D-mannitol, indicating paracellular moveme nt for both compounds. From these data, it is concluded that, under th e experimental conditions used, LLC-PK1 cells do not exhibit a specifi c transcellular transport system for oxalate.