BASOLATERAL DISTRIBUTION OF CAVEOLIN-1 IN THE KIDNEY - ABSENCE FROM H-ATPASE-COATED ENDOCYTIC VESICLES IN INTERCALATED CELLS()

In kidney epithelial cells, a variety of physiological processes are d ependent on the active recycling of membrane proteins between intracel lular vesicles and the cell surface. Although clathrin-mediated endocy tosis occurs in several renal cell types, endocytosis can also occur b y non-clathrin-coated vesicles, including pinocytotic structures known as caveolae that contain a novel coat protein, caveolin. Exo- and end ocytosis of a vacuolar H+-ATPase in intercalated cells also occurs via specialized ''coated'' vesicles that do not contain clathrin. The aim of this study was to localize caveolin in the kidney and, in addition , to determine whether it could be a component of the H+-ATPase recycl ing process. Using an antibody against the alpha- and beta-isoforms of caveolin-1, our immunocytochemical data show a marked heterogeneity i n the cellular expression of this isoform of caveolin in kidney. In co ntrast, caveolin-3 was not detectable in renal epithelial cells. Caveo lin-1 was abundant in endothelial cells and smooth muscle cells and wa s present in the parietal cells of Bowman's capsule. Distal tubule cel ls, connecting tubule cells, and collecting duct principal cells exhib ited marked punctate basolateral staining, corresponding to the presen ce of caveolae detected by electron microscopy, whereas all intercalat ed cells were negative in both cortex and medulla. These data indicate that although caveolin-1 may participate in basolateral events in som e kidney epithelial cell types, it does not appear to be involved in t he regulated recycling of H+-ATPase in intercalated cells. Therefore, these cells recycle H+-ATPase by a mechanism that involves neither cla thrin nor caveolin-1.