POLARIZED LOCALIZATIONS OF ANNEXIN-I, ANNEXIN-II, ANNEXIN-VI AND ANNEXIN-XIII IN EPITHELIAL-CELLS OF INTESTINAL, HEPATIC AND PANCREATIC TISSUES

The cellular and subcellular localizations of annexins I, II, VI and X III in the rabbit intestine, liver and pancreas were studied by perfor ming immunofluorescence labeling on thin frozen tissue sections using specific monoclonal antibodies. The expression of annexins was found t o be finely regulated. Annexins XIII and I were expressed exclusively in the small intestine and the colon, respectively, whereas annexin II was present in all the tissues tested and annexin VI specifically in the liver and pancreas. These different annexins were concentrated in the basolateral domain of polarized cells, and some of them had an ext ra-apical localization: annexin XIII was concentrated in the lower 3/4 of enterocyte brush border microvilli; annexin II was present in the upper part of the terminal web in intestinal absorbent cells as well a s in the bile canalicular area in hepatocytes, whereas annexin VI was detected on some apical vesicles concentrated around the bile canalicu li, In pancreatic acinar cells, the presence of annexin II on some zym ogen granules provides further evidence that annexin II may be involve d in exocytic events. In conclusion, this study shows that the basolat eral domain of polarized cells appears to be the main site where annex ins are located, and they may therefore be involved in the important c ellular events occurring at this level.