Epithelial cells plasma membrane

Eukaryotic cell plasma membranes Muscle sarcoplasmic reticulum Eukaryotic cell plasma membranes Stomach epithelial cell plasma membranes... 

Brasitus, TA Universitx of Chicago Colonic epithelial cell plasma membranes NIH, NCI... 

The location of transporters at the cell plasma membrane is a critical issue because most of the cells involved in the A, D, E pharmacokinetic processes are polarized. Hence then-apical (luminal) and basolateral (abluminal) membranes do not have the same populations of transporters (Eigure 34.4). The same transporter is rarely found at both the apical and basolateral membranes. But most of the ABC and SLC transporters are located at either the apical or the basolateral epithelial membranes, and their location helps to define the direction of substrate transport and the resulting pharmacokinetic event. 

In the tongue, ENaC is expressed in taste bud epithelial cells. The expression of a, (3 and y subunits at the apical membrane of taste buds is observed under low salt diet, known to greatly increase plasma aldosterone. This observation suggests that ENaC could play a significant role in the transduction of salt sensation. 

Bundles of parallel actin filaments with uniform polarity. The microvilli of intestinal epithelial cells (enterocytes) are packed with actin filaments that are attached to the overlying plasma membrane through a complex composed of a 110-kD protein and calmodulin. The actin filaments are attached to each other through fimbrin (68 kD) and villin (95 kD). The actin bundles that emerge out of the roots of microvilli disperse horizontally to form a filamentous complex, the terminal web, in which several cytoskeletal proteins, spectrin (fodrin), myosin, actinin, and tropomyosin are present. Actin in the terminal web also forms a peripheral ring, which is associated with the plasma membrane on the lateral surfaces of the enterocyte (see Figure 5, p. 24). 

The cytoskeleton is involved in the maintenance of cell shape and cytoplasmic processes (e.g., microvilli). In polarized epithelial cells, distinct cyto-cortical cytoskeletal complexes are associated with the apical and basal-lateral domains of the plasma membrane (Rodriguez-Boulan and Nelson, 1989 Mays et al., 1994). 

Biochemical studies of plasma membrane Na /H exchangers have been directed at two major goals (1) identification of amino acids that are involved in the transport mechanism and (2) identification and characterization of the transport pro-tein(s). To date, most studies have been performed on the amiloride-resistant form of Na /H" exchanger that is present in apical or brush border membrane vesicles from mammalian kidney, probably because of the relative abundance of transport activity in this starting material. However, some studies have also been performed on the amiloride-sensitive isoform present in non-epithelial cells. 

The third mucosal layer is that lining the entire length of the small intestine and which represents a continuous sheet of epithelial cells. These epithelial cells (or enterocytes) are columnar in shape, and the luminal cell membrane, upon which the microvilli reside, is called the apical cell membrane. Opposite this membrane is the basal (or basolateral) plasma membrane, which is separated from the lamina propria by a basement membrane. A sketch of this cell is shown in Fig. 5. The primary function of the villi is absorption. 

Another way to increase the entry of Ca2+ across the plasma membrane is to hyperpolarize the plasma membrane by elevating active ion transport. Fischer et al. [130] demonstrated that hyperpolarization of colonic epithelial cells (HT-29) with carbachol elevates the intracellular levels of Ca2+, [Ca2+]i while depolarization with gramicidin D or elevation of K+ in the bathing fluid reverses it. Treatment with 0.1 mM carbachol produced a spontaneous increase in [Ca2+]i from 63 nM to 901 nM. This lasted for about 3 min, beyond which a plateau level of 309 nM was maintained. While the initial Ca2+ transient was present in Ca2+-free medium containing 0.1 mM EGTA, the plateau phase was suppressed to baseline levels, suggesting that carbachol initially releases Ca2+ from the intracellular stores and subsequently increases the Ca2+ entry across the plasma membrane. In cells hyperpolarized with carbachol, induction of depolarization by ele-... 

PS Reinach, N Holmbeg, R Chiesa. (1991). Identification of calmodulin-sensitive Ca2+-transporting ATPase in the plasma membrane of bovine corneal epithelial cell. Biochim Biophys Acta 1068 1-8. 

Formation of Na+, K+-ATPase carrier molecules in the basolateral membrane of the tubular epithelial cells (promotes extrusion of Na+ ions from the cells and their movement into plasma by way of peritubular capillaries enhances the concentration gradient for passive diffusion through Na+ channels in the luminal membrane)... 

Attempts to study the entry of ES products into cells using markers of fluid phase endocytosis yielded unexpected results. When larvae browse resistant IEC-6 cells in the presence of extracellular fluorescent dextran, dextran enters the cytoplasm of a significant proportion of the cells in the mono-layer (Butcher et al., 2000). The parameters of dextran entry are most compatible with the conclusion that larvae wound the plasma membranes of IEC-6 cells that is, they create transient breaches in the membrane that allow impermeant markers to enter the cell (McNeil and Ito, 1989). Wounding is considered to be a common occurrence in intestinal epithelia (McNeil and Ito, 1989). Injured cells are able to heal their wounds by recruiting vesicles to seal the breach (Steinhardt et al., 1994). In an experimental system, healing allows the injured cell to retain cytoplasmic dextran. In epithelial cell cultures inoculated with T. spiralis larvae, the relationship between glycoprotein delivery and injury of plasma membranes is not clear, i.e. dextran-laden cells do not always stain with Tyv-specific antibodies and... 

Butcher, B.A., Gagliardo, L.F., ManWarren, T. and Appleton, J.A. (2000) Larvae-induced plasma membrane wounds and glycoprotein deposition are insufficient for Trichinella spiralis invasion of epithelial cells. Molecular and... 

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