Regular structures on the microvillar surface membrane of ileal epithelial cells in suckling rat intestine.

Freeze-fracture deep-etch studies were done to examine regular patterns of surface membrane particles in the suckling rat ileal epithelium by using quick-freezing method. In addition to the presence on the luminal surfaces of well-developed endocytic complexes, latticed particles were consistently observed on almost the entire apical membrane between microvilli and frequently on the microvilli. These particles seemed to be partly integrated in the outer half layer of membranes. After rinsing with phosphate-buffered saline, patterns on the microvilli appeared to be parallel circle lines rather than latticed particles found in fresh preparations. Filipin treatment showed the presence of filipin-sterol complexes on most of the particle-covered membrane areas except small tubules and vesicles. Possibilities were suggested that these latticed particles were transferred to the apical surface along the outer half layer of membranes, and released or secreted into the intestinal lumen.