ANNEXINS IN RAT ENTEROCYTE AND HEPATOCYTE - AN IMMUNOGOLD ELECTRON-MICROSCOPE STUDY

In the present study, immunogold labeling of ultrathin sections of rat small intestine and liver has been used to obtain insights into the u ltrastructural localization and possible functions of annexins. In ent erocytes, annexins II, IV, and VI are found at the periphery of the co re of each microvillus and of the rootlets, but are absent from the in terrootlet space. Annexins II, IV, and VI are also observed close to t he interdigitated plasma membrane. In hepatocytes, only annexin VI is found to be concentrated within the microvilli in the bile canaliculi, on the inner face of the sinusoidal cell surface, particularly in the space of Disse, and all along the plasma membrane. Annexin VI is also detected in mitochondria of enterocytes and hepatocytes. These locali zations are in agreement with the concept of a close calcium-dependent association of annexins with membranes and cytoskeletal proteins, par ticularly with actin. Moreover, they support the hypothesis of an invo lvement of annexins in exocytotic and endocytotic processes, which tak e place in epithelial cells.