Maturation of tight junctions in guinea-pig cecal epithelium.

By means of the freeze-fracture technique and in tracer studies it is demonstrated that the structure of tight junctions and the permeability to lanthanum of the guinea-pig cecal epithelium change during maturation of cells. Height and strand number of tight junctions in the apical-basal direction increase as crypt cells migrate to the surface of the epithelium. Likewise, the interlacing of continuous strands was greater in surface than in crypt junctions. The numerous free-ends, isolated individual free-strands and maculae occludentes found in crypt cells were absent in surface epithelial cells. Goblet cells, located at the bottom of crypts, displayed tight junctions similar in characteristics to those of cells located in the middle region of crypts. Cells at the surface and in middle regions of crypts possess tight junctions impermeable to lanthanum, whereas junctions between cells located at the bottom of crypts often were permeable to the tracer, indicating that permeability decreases as the epithelial cells mature. Genesis and maturation mechanisms related to structural configuration of tight junctions are discussed.