A distal nephron glycoprotein that has different cell surface distributions on MDCK cell sublines

Monoclonal antibodies that recognize three distinct epitopes of a 23-kDa glycoprotein (gp23) on the plasma membrane of MDCK cells were used to study cell-surface polarity. Immunofluorescence microscopy of MDCK cells obtained from the American Type Culture Collection demonstrated that gp23 was nonpolarized in approximately 50% of the cells (on both apical and basolateral membranes), whereas, in the remaining cells, gp23 had a polarized distribution (basolateral only). This heterogeneous gp23 cell-surface staining was not observed in a variety of other MDCK sublines. Instead, gp23 was found to have a nonpolarized distribution on MDCK cells that produced monolayers with low transepithelial electrical resistances (less than 220 omega X cm2) and was localized only to the basolateral membrane of MDCK cell lines capable of generating considerably higher transepithelial electrical resistances (770-2,220 omega X cm2). Immunofluorescence and immunoelectron microscopy of dog, rat, and rabbit kidney demonstrated that gp23 is a nephron segment-specific glycoprotein localized only to the distal and collecting tubules. These observations provide further evidence for the heterogeneity of the MDCK cell line. They also support a proposal that the origin of MDCK cells is the renal distal nephron.