LOCALIZATION OF ALANINE UPTAKE BY CULTURED RENAL EPITHELIAL-CELLS (LLC-PK1) TO THE BASOLATERAL MEMBRANE

Alanine uptake by LLC-PK1 cells [from pigs] was previously demonstrated to be almost exclusively Na dependent. When the cells are grown on an impermeable substratum there is a marked fall in uptake as confluence is reached. By applying an autoradiographic tehcnique to visualize transported alanine, it is clear, that even in subconfluent cultures there is marked cellular inhomogeneity with regard to uptke, which takes place predominantly in those cells at the periphery of growing islands and not those at the interior. When cells are grown on permeable substrata, a uniform distribution of Ag grains is found. In 2 other types of experiment, it was found that when confluent cell monolayers on an impermeable support were treated briefly with a chelating agent or suspended by mechanical treatment, there was a marked increase per cell in Na dependent alanine uptake and in ouabain-sensitive potassium uptake. The apparent fall in alanine uptake as cells reach confluence on an impermeable support is due to masking of transport sites, which are predominantly, if not exclusively, located at the basolateral membrane.