TIGHT JUNCTION DISRUPTION AND RECOVERY AFTER SUBLETHAL GAMMA-IRRADIATION

Ilea from sublethally irradiated, adult rats were prepared for freeze-fracture and lanthanum tracer study to investigate the alterations that occur in the structure and function of the intestinal permeability barrier. Some of the tight junction structures were determined to be focally disrupted between Days 1 and 5 postirradiation using the freeze-fracture technique. Alterations in the mean depth of the apical tight junction appeared to correlate with the permeability of the epithelium to lanthanum tracer. The occurrence of tight junctional fragments over extensive areas between lateral membrane fracture faces were observed during the disruption and recovery phases and were manifested as linear and macular tight junctions that extended basally from the apical tight junction (zonula occludens) as far as the basal lamina. These 'proliferative' tight junction fragments were thought to be eventually removed by phagocytosis since numerous tight junctional fragments could be observed in cytoplasmic vesicles between Days 3 and 7 after irradiation. Lanthanum tracer, which was added only to the intestinal lumen during fixation for electron microscopy, was found in extracellular spaces between some goblet and adjacent absorptive epithelial cells in preparations from irradiated rats. 'Leaky' tight junctions were observed between Days 1 and 7 postirradiation, thereupon returning to control levels.