Microvillus

Matsudaira, P.T. Burgess, D.R. (1979). Identification and organization of the components in the isolated microvillus cytoskeleton. J. Cell. Biol. 83,667-673. 

TA Brasitus, R Dahiya, PK Dudeja, BM Bissonnette. Cholesterol modulates alkaline phosphatase activity of rat intestinal microvillus membranes. J Biol Chem 263 8592-8597, 1988. 

The microvillar surface is coated with a layer of electron-dense amorphous material (glycocalyx). In H. contortus, helical filaments composed of contortin are associated with this layer and fill the spaces between the microvilli. There can be up to ten strands of contortin in each microvillus ... 

Nramp2 across microvillus 1997) Belgrade (b) rat unresponsive to oral iron... 

D., Fransen, J. A. M., Marxer, A., Expression and intracellular transport of microvillus hydrolases in human intestinal epithelial cells, J. Cdl Biol. 1985, 101, 838-851. 

EPEC causes a degeneration of the microvillus brush border, with cupping and pedestal formation of the plasma membrane at the sites of bacterial attachment and reorganization of cytoskeletal proteins [43, 44], Invasion has been observed in some clinical specimens, but the mechanism of how this bacteria produces diarrhea is not fully understood. Some possibilities include an increase in permeability and loss in microvilli leading to malabsorption. 

Primarily to elucidate transporter localization and function, vesicles enriched in trophoblast apical or basolateral membranes have frequently been utilized. To give a few instances, they have been used to investigate P-gp-mediated transport, mechanisms of transport of cationic compounds, drug interactions with nutrient transport, and differences in amino acid transport in pathological conditions of the placenta [36, 40-42], Briefly, for preparation of microvillus membrane vesicles the cord, amniochorion and decidua are removed from placenta, and the tissue cut on the maternal side. The mince is stirred to loosen... 

Glenney, J. R., Jr., Kaulfus, P., Matsudaira, P., and Weber, K. (1981). F-actin binding and bundling properties of fimbrin, a major cytoskeletal protein of microvillus core filaments. / Biol. Chem. 256, 9283-9288. 

Bretscher, A., and K. Weber. 1979. Villin the major microfilament-associated protein of the intestinal microvillus. Proc Natl Acad Sci USA. 76 2321—5. 

The microvillus membrane of the absorptive cell has a thickness of 9 5-11.5 nm, which is somewhat thicker than normal biological membranes. It is folded into microvilli (about 200,000/mm2 in the human jejunum [11]), and increases the surface of the intestine by a factor of 20. Microvilli contract, and, during contraction the fibers in the core slide down toward the underlying terminal web. In this region, the movement of dings and other molecules will not only be diffusive but also agitalive. Molecules passing the membrane are absorbed by the trans-cel lular" pathway. 

To elucidate the role ofhydrophobic bonding, a detailed study on the kinetics ofin-testinal absorption has been performed on sulfonamides. It was concluded that transport across the microvillus membrane occurs via kinks in the membrane which are pictured as mobile structural defects representing mobile free volumes in the hydrocarbon phase of the membrane and whose diffusion coefficient is fairly fast ( 10-5 cm2/s) [1]. The thermal motion of the hydrocarbon chain leads to the formation of kinks. It was also postulated that a transient association of the drug molecules with proteins on the surface of the microvillus membrane is involved in the formation of the activated complex in the absorption process [1]. 

Aronson, P.S., Nee, J., Suhm, M.A. (1982). Modifier role of internal H+ in activating the Na+/H+ exchanger in renal microvillus membrane vesicles. Nature 299,161-163. 

Fig. 8.6. Paricterotaenia paradoxa-. development of microtriches from microvilli in the polycephalic larva (not to scale), (a) The original microvillus. (b) and (c) The microvillus base swells and contains peripheral electron-dense material, (d) A developing microthrix on the posterior neck region of larva the original microvillus is still attached, (e) A mature, modified microthrix on the posterior neck region. (/) A developing microthrix on the anterior neck region, the original microvillus is still attached, (g) A mature microthrix on the anterior neck region. (After MacKinnon Burt, 1984.)...

Stern M, Gellermann B. Food proteins and maturation of small intestinal microvillus membranes (MVM). I. Binding characteristics of cows milk proteins and concanavalin A to MVM from newborn and adult rats. J Pediatr Gastroenterol Nutr 1988 7 115-121. 

Figure 25-4. Model of the molecular forms of lactase during synthesis and processing in the human villus enterocyte. MVM, microvillus membrane.

Dan T, Onuma E, Tanaka H, Koga H (1991) A selective uricosuric action of AA-193 in rats. Comparison with its effect on PAH secretion in vivo and in vitro. Naunyn-Schmiedeberg s Arch Pharmacol 343 532-537 Kahn AM, Branham S, Weinman EJ (1983) Mechanism of urate and p-aminohippurate transport in rat microvillus membrane vesicle. Am J Physiol 245 (Renal Fluid Electrolyte Physiol 14) F151-F158... 

Villin is an example of a bundling protein. Villin is found in the microvilli of, for example, intestinal brush border cells (Fig. 5-30). The microvilli greatly increase the surface area of the cells, which is essential for effective absorption to take place. Each microvillus extends about 2 p.m into the lumen of the gut and is supported by 20 or so actin filaments tightly bundled by villin (and other proteins) at regular intervals. In a feature common to many actin-based networks, all the filaments in the bundle are oriented with their barbed ends in the same direction, in this case toward the tip of the microvillus where they terminate. Cross-linking of the actin filaments to the plasma membrane occurs via a second protein from the myosin-1 family (a relative of the well-known contractile protein myosin-II). This protein binds its head domain to the sides of the filaments and embeds its tail domain into the membrane. 

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