The enteric surface coat on cat intestinal microvilli

Brush border development in the intestinal absorptive cells of Xenopus during metamorphosis

The differentiation of the brush border which makes up the apical free surface of intestinal absorptive cells has been studied by electron microscopy. Specimens of Xenopus small intestine were fixed at various stages during metamorphosis, the time when a new intestinal epithelium forms. The interpretation of details described herein emphasizes the role of "surface-forming" vesicles. These vesicles are thought to provide membrane both for the initial expansion of the apical surface and for the later elongation of the microvilli. The latter are believed to be "molded" around filamentous cores that appear early in differentiation. The cores are attached to the apical membrane and extend vertically into the supranuclear cytoplasm. This interpretation rests chiefly on (a) the resemblance, both in morphology and in staining properties with colloidal thorium, between the membrane that limits the vesicles and that which limits the microvilli and (b) the distribution and time of appearance of the vesicles with respect to development of the microvilli. According to this view, the specific properties of surface membrane reside in preformed units that arise within the supranuclear cytoplasm. This morphogenetic process probably involves participation of the Golgi region as the site where the complex macromolecular architecture of the cell surface is assembled.

Cortical cytoplasmic filaments of cleaving eggs: a structural element corresponding to the contractile ring

A sheath consisting of filaments 50-70 A in diameter has been demonstrated in association with the expanded, leading margins of the cleavage furrow in unilaterally and symmetrically cleaving eggs of a jellyfish and a polychaete worm, respectively. The observations suggest that the filament system might provide a structural basis for the existence of the contractile gel that, according to a hypothesis by Marsland and Landau, accomplishes cleavage. The filamentous sheath is present only in the furrow region and is arranged in an arcuate manner in unilaterally cleaving eggs and circumferentially in symmetrical cleavage. The filaments appear to be of finite length, and a number of them must overlap to span the length of the furrow. Contraction may be accomplished if the filaments slide relative to each other. However, contraction per se was experimentally not demonstrated in the studied systems. The disappearance of microvilli and the merocrine type secretion of mucoid droplets at the interdigitating or "spinning" membrane region of unilateral cleavage suggest that the unfolding of a pleated membrane and the insertion of intracytoplasmic membranes might contribute, at least in part, to the necessary extra cell membrane.

A study of the small intestinal mucosa using the scanning electron microscope

In this paper we describe the features of small intestinal structure in normal control subjects using the scanning electron microscope.

The "vesicle in a basket". A morphological study of the coated vesicle isolated from the nerve endings of the guinea pig brain, with special reference to the mechanism of membrane movements

Five points are discussed regarding the vesicular structure isolated by fractionation techniques from the brain and liver of the guinea pig. 1. One type of vesicle, fixed by OsO(4) and shown in thin sections, is identified with the coated vesicle that has been observed in many varieties of tissues. 2. The vesicle contained in a spherical polygonal "basketwork" shown by the negative-staining techniques is identical with the coated vesicle shown in sections. 3. Despite minute observation of this basketwork we could not confirm the existence of "hairlike projections" extending from the convex cytoplasmic surface of the vesicle. We are inclined to believe, therefore, that the hairlike projections are actually the superimposed visual images of the regular hexagons and pentagons of the network composing the basketwork. 4. We repeat the hypothesis originally advanced by Roth and Porter (1) that the "coating" of the coated vesicle plays a role in the mechanism of the infolding and fission of the membrane; we suggest that these events are caused by the transformation of the regular hexagons (of the coating) into regular pentagons. 5. Finally, we make a suggestion as to the nature of those vesicles which have on their surface subparticles which look like "elementary particles (2)."

Undescribed endothelial processes of the choriocapillaris extending to the retinal pigment epithelium of the chick

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Membrane modifications in the apical endocytic complex of ileal epithelial cells

Ileal lining cells of the suckling rat possess an "apical endocytic complex" capable of sequestering intact protein from the intestinal lumen. The complex consists of a network of invaginations of the apical plasma membrane, a number of subjacent small vesicles, and a giant supranuclear vacuole. The first two components initially incorporate material from the intestinal lumen and then transfer it to the giant vacuole where it is stored. Their limiting membrane displays striking structural modifications when viewed in various planes of section. Its lumenal dense leaflet appears discontinuous and consists of an ordered array of minute discrete plaques. A dense particle approximately 70 A in diameter is centered over each plaque. The particles are arranged in a two-dimensional square lattice with center-to-center spacing of approximately 120 A.

Cytochemistry of pulmonary alveolar epithelial cells

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The fine structure of Brunner's glands in man

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Lipid composition of the isolated rat intestinal microvillus membrane

1. Rat intestinal microvillus plasma membranes were prepared from previously isolated brush borders and the lipid composition was analysed. 2. The molar ratio of cholesterol to phospholipid was greatest in the membranes and closely resembled that reported for myelin. 3. Unesterified cholesterol was the major neutral lipid. However, 30% of the neutral lipid fraction was accounted for by glycerides and fatty acid. 4. Five phospholipid components were identified and measured, including phosphatidylethanolamine, phosphatidylcholine, phosphatidylserine, sphingomyelin and lysophosphatidylcholine. Though phosphatidylethanolamine was the chief phospholipid, no plasmalogen was detected. 5. In contrast with other plasma membranes in the rat, the polar lipids of the microvillus membrane were rich in glycolipid. The cholesterol:polar lipid (phospholipid+glycolipid) ratio was about 1:3 for the microvillus membrane. Published data suggest that this ratio resembles that of the liver plasma membrane more closely than myelin or the erythrocyte membrane. 6. The fatty acid composition of membrane lipids was altered markedly by a single feeding of safflower oil. Membrane polar lipids did not contain significantly more saturated fatty acids than cellular polar lipids. Differences in the proportion of some fatty acids in membrane and cellular glycerides were noted. These differences may reflect the presence of specific membrane glycerides.

Antibodies to intestinal microvillous membranes. I. Characterization and morphologic localization

Antibodies (AbMVM) were produced in rabbits to microvillous membranes isolated from hamster small bowel. Incubation of frozen sections of hamster small bowel with fluorescein-labeled AbMVM showed specific reaction with brush borders, but not with other intestinal cellular components. Electron microscopy with ferritin-conjugated AbMVM localized the antigens more precisely to the surface mucopolysaccharide coat of the brush borders. AbMVM also reacted with the brush border of colon and of proximal renal tubules of hamsters but not with those of hamster stomach or gall bladder. It also reacted with the brush borders of some rat and human tissues, but not with those of rabbits. In addition, fluorescent-labeled AbMVM combined specifically with cell walls of some yeasts, but not of several bacteria. AbMVM also contained a weak precipitin to a component of hamster serum, which migrated like prealbumin in immunoelectrophoresis.