EXPRESSION AND CELLULAR DISTRIBUTION OF PRIMARY-, SECONDARY- AND TERTIARY-ACTIVE BASOLATERAL MEMBRANE TRANSPORTERS FOR ORGANIC ANIONS IN HUMAN KIDNEYS

In human kidneys, endogenous and exogenous organic anions (OA) are removed by organic anion transporters (OAT) that belong to the SLC family of transporters and reside in the basolateral membrane (BLM) of epithelial cells along the nephron, pedominantly in proximal tubules. The active contributors to this process are the primary-active sodium-potassium adenosine triphosphatase (Na/K-ATPase), secondary-active sodium-dicarboxylate cotransporter 3 (NaDC3/SLC13A3) and tertiary-active OA exchangers OAT1/SLC22A6, OAT2/SLC22A7, and OAT3/SLC22A8. Several previous studies showed that the expression of renal OAT1-3 was sex-dependent in rodents (rats and mice), but similar investigations in human kidneys have not been reported. Accordingly, here we studied the expression and distribution of various BLM transporters that contribute to OA secretion along the human nephron by immunofluorescence cytochemistry (IC) in tissue cryosections and by Western blotting (WB) of total cell membranes (TCM) isolated from the kidneys of men (M ; n = 7 ) and women (W ; n = 9). Virtually healthy kidney tissue was obtained following surgical removal of the carcinoma-diseased organs. Specificity of the used polyclonal antibodies for human NaDC3 and OAT1-3 was confirmed in the transporters-transfected HEK293 cells by IC and WB, whereas the proper transfection was validated in uptake experiments with radiolabeled succinate (NaDC3), p-aminohippurate (OAT1), cGMP (OAT2) and estrone-3-sulfate (OAT3). In IC studies, in human kidneys we confirmed colocalization of Na/K-ATPase, NaDC3 and OAT1-3 in the proximal tubule BLM, whereas Na/K-ATPase and NaDC3 were also colocalized in the BLM of collecting ducts. In WB of TCM, the protein bands of ~85, ~80, ~75 and ~110 kDa were detected for OAT1, OAT2, OAT3 and Na/K-ATPase, respectively, whereas two protein bands of 70 and 90 kDa were detected for NaDC3. The density of protein bands in WB studies, and the staining intensity of various transporters in IC studies were similar in M and W kidneys. Therefore, various primary-, secondary- and tertiary-active transporters that contribute to OA secretion along the human nephron exhibit fair colocalization in the proximal tubules, but in more distal nephron segments, the co-expression is restricted to Na/K-ATPase and NaDC3. Sex differences in the expression of tested transporters were not observed, thus indicating that the sex-dependent expression of some renal transporters is species-related.