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

The dynamics of gap junction protein connexins (CXN) in the developing rat exorbital lacrimal gland cells were examined by immunofluorescenc e and electron microscopy. Indirect double-staining immunofluorescence histochemistry of unfixed frozen sections of the exorbital lacrimal g land 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 CX N 26 was detected, but the immunoreaction of CXN 32 was negligible. Di minutive gap junction plaques were identified on protoplasmic fracture faces (P face) of freeze fracture replicas. The immunoreaction of; CX N 32 was first detected on postnatal day 11. The immunoreactions of CX N 26 and 32 were detected at almost the same site of the acinar cell l ateral aspect. The immunoreaction was not detected in the duct epithel ium of the lacrimal gland. As the age advanced, the immunoreactivity o f CXN 26 and 32 increased in both quantity and intensity. Seventeen da ys after birth when the rat eyelids opened, the intensity and distribu tion of CXN 26 and 32 immunoreactivity were approximately equal to tho se of the rats of postnatal day 25. Electron microscopy of ultrathin s ections and freeze fracture replicas also revealed gap junctions. Twen ty-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 postnat al days 17-25. The number of secretory granules in acinar cells increa sed with age. Gap junctions increased in size with age as revealed by freeze fracture replicas. These findings indicate that gap junctions d evelop as the secretory activity of acinar cells is up regulated in th e exorbital lacrimal gland.