DYNAMICS OF GAP JUNCTION PROTEIN CONNEXINS IN RAT EXORBITAL LACRIMAL GLANDS DURING POSTNATAL STAGES

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The dynamics of gap junction protein connexins (CXN) in the developing rat exorbital lacrimal gland cells were examined by immunofluorescence and electron microscopy. Indirect double-staining immunofluorescence histochemistry of unfixed frozen sections of the exorbital lacrimal gland showed that the gap junctions in the rat exorbital lacrimal gland cells were composed of proteins which were immunologically equivalent to CXN 26 and 32. Six days after birth, a slight immunoreaction of CXN 26 was detected, but the immunoreaction of CXN 32 was negligible. Diminutive gap junction plaques were identified on protoplasmic fracture faces (P face) of freeze fracture replicas. The immunoreaction of CXN 32 was first detected on postnatal day 11. The immunoreactions of CXN 26 and 32 were detected at almost the same site of the acinar cell lateral aspect. The immunoreaction was not detected in the duct epithelium of the lacrimal gland. As the age advanced, the immunoreactivity of CXN 26 and 32 increased in both quantity and intensity. Seventeen days after birth when the rat eyelids opened, the intensity and distribution of CXN 26 and 32 immunoreactivity were approximately equal to those of the rats of postnatal day 25. Electron microscopy of ultrathin sections and freeze fracture replicas also revealed gap junctions. Twenty-five days after birth, nearly all cells showed distinctly positive immunoreactions of CXN 26 and 32, the feature similar to that of adult rats. These findings showed that gap junctions gradually increased in number postnatally and reached almost the adult level between postnatal days 17-25. The number of secretory granules in acinar cells increased with age. Gap junctions increased in size with age as revealed by freeze fracture replicas. These findings indicate that gap junctions develop as the secretory activity of acinar cells is up regulated in the exorbital lacrimal gland.