EXPRESSION OF THE MOUSE NA-K-2CL COTRANSPORTER, MBSC2, IN THE TERMINAL INNER MEDULLARY COLLECTING DUCT, THE GLOMERULAR AND EXTRAGLOMERULAR MESANGIUM, AND THE GLOMERULAR AFFERENT ARTERIOLE

Na-K-Cl cotransport plays an important role in the kidney in NaCl reab sorption in the thick ascending limb of Henle and a less well defined role in the inner medullary collecting duct (IMCD). Two Na-K-Cl cotran sporters encoded by different genes have been identified in the mammal ian kidney: BSC1/NKCC2 which localizes to the apical thick ascending l imb of Henle and BSC2/NKCC1 which was isolated from a mouse IMCD cell line (mIMCD-3) but its localization has not been determined. In this s tudy we generated a polyclonal antibody (anti-mBSC2) against the mouse BSC2/NKCC1 protein in order to characterize and localize this protein in mouse kidney. Western blot analysis with affinity-purified anti-mB SC2 showed a protein doublet of 140 and 150 kD which was most abundant in the renal papilla but also seen in cortex and outer medulla. The 1 40-150-kD bands were not seen with preimmune serum or with anti-mBSC2 preabsorbed with specific antigen. Immunolocalization confirmed expres sion of mBSC2 protein on the basolateral surface of terminal IMCD segm ents and demonstrated expression in the papillary surface epithelium. Immunofluorescence also revealed the unexpected presence of the BSC2 p rotein at the juxtaglomerular afferent arteriole, in a juxtaglomerular structure probably representing the extraglomerular mesangium, and th roughout the glomerular mesangium.