Identification and localization of TRPC channels in the rat kidney

It is well established that transient receptor potential (TRP) channels are activated following stimulation of G protein-coupled membrane receptors linked to PLC, but their differential expression in various cells of the renal nephron has not been described. In the present study, immunoprecipitations from rat kidney lysates followed by Western blot analysis using TRPC-specific, affinity-purified antibodies revealed the presence of TRPC1, -C3, and -C6. TRPC4, -C5, and -C7 were nondetectable. TRPC1 immunofluorescence was detected in glomeruli and specific tubular cells of the cortex and outer medulla. TRPC1 colocalized with aquaporin-1, a marker for proximal tubule and thin descending limb, but not with aquaporin-2, a marker for connecting tubule and collecting duct cells. TRPC3 and -C6 immunolabeling was predominantly confined to glomeruli and specific tubular cells of the cortex and both the outer and inner medulla. TRPC3 and -C6 colocalized with aquaporin-2, but not with the Na(+)/Ca(2+) exchanger or peanut lectin. Thus TRPC3 and -C6 proteins are expressed in principle cells of the collecting duct. In polarized cultures of M1 and IMCD-3 collecting duct cells, TRPC3 was localized exclusively to the apical domain, whereas TRPC6 was found in both the basolateral and apical membranes. TRPC3 and TRPC6 were also detected in primary podocyte cultures, whereas TRPC1 was exclusively expressed in mesangial cell cultures. Specific immunopositive labeling for TRPC4, -C5, or -C7 was not observed in kidney sections or cell lines. These results suggest that TRPC1, -C3, and -C6 may play a functional role in PLC-dependent signaling in specific regions of the nephron.