Tight junctions in the rat parotid gland

The aim of this study was to elucidate the distribution and morphological c hanges of tight junctions during secretion in parotid gland acinar cells. L ocalization of tight junction-associated polypeptide ZO-1, and of tight jun ction transmembrane protein Occludin, was examined in rat parotid gland by immunofluorescence and immunogold labelling of ultrathin sections. Adult ma le Sprague-Dawley rats were intraperitoneally injected with IPR and, after 10 and 30 minutes, parotid glands were extirpated. In control specimens. po sitive immnnoreaction for ZO-1 and Occludin was observed on: the adluminal side between adjacent cells in the form of narrow elongated profiles corres ponding to intercellular canaliculi. After IPR injection, canaliculi became dilated and fluorescence was no longer seen as a continuous line but appea red as an aggregation of separate bright particles. ZO-1 was more widely di stributed and was recognized in other areas of the cytoplasm as well. Concu rrently, omega-shaped concavities, marked by actin fluorescence, appeared a long the intercellular canaliculi. We concluded that, during exocytosis, th e selective permeability barrier to the paracellular pathway, based on tigh t junctions, becomes more leaky, owing to segregation of Occludin caused by intracellular ZO-1 distributional changes associated with actin filaments.