Transport tissue types

Transport in the nephron is mechanistically similar to that in the gut and indeed the two tissue types have essentially identical properties. Substances moving between the... 

Selection of the cell line or tissue type influences not only the technique for membrane vesicle preparation but also the resulting percentage of inside-out-oriented plasma membrane vesicles. A sufficient amount of inside-out-oriented vesicles is essential, since only this fraction, with the ATP-binding domains oriented to the outer surface, mediates ATP-dependent transport of a labeled substrate into the vesicle. 

In 1993, the Menkes gene was isolated and shown to be a copper transporting P-type APTase protein, ATP7A (Suzuki et al. 1999). The Menkes protein is expressed in most tissues, except liver. The disease locus was mapped to Xql3.3, and the gene has been isolated by means of positional cloning (Turner et al. 1999). 

Other tissue types mouse brain,rat skeletal muscle,and isolated villus cells. Conversely, vanadate inhibited glucose transport in rat intestine when added to the perfusate of an everted gut sac preparation, or when added as a supplement to the drinking water of diabetic and non-diabetic rats at concentrations up to 0.08 mM for 2-4 weeks. ... 

Transmembrane movement of sucrose is accomplished by transport proteins in several, but not all tissue types. The most obvious example of a specific tissue type is the phloem. The sucrose concentration in this tissue can approach 0.8 M in contrast to mM concentration in the surrounding tissues and probably sub mM concentration in the extra cellular spaces surrounding the phloem (2). Transport into the cells of the phloem is difficult to study as they are an integral part of the leaf or stem structure, and may comprise only 5 to 10% of the total leaf mass. Another example of sucrose transport is the accumulation of sucrose and other nutrients by cells of... 

Fig. 3.3. Time course of radiocarbon accumulation in basal agar receivers of 8-mm sections of tobacco stem tissues, apically supplied with agar donor blocks containing l i C IAA (3 pM). The linear regression equations and the lines of closest fit were estimated by the least-squares method from the data beyond 1.5 h for tissue types 1, 2 and 3, and 2.5 h for tissue types 4 and 5 (the last time value was ignored for the inner tissues since it showed a decline in the export rate after a transport period of about 3.5 h in other experiments). Note that small amounts of radioactivity were found in the receivers from all tissue types before the intersections of the straight lines. (Data from Sheldrake 1973 a)...

The importance of surface membrane functions differs in various cell and tissue types. Intestinal mucosal cells and kidney tubule cells represent cell systems highly specialized for moving substances across cell membranes. The transport processes in the intestine and kidney are essential for obtaining and reclaiming from the environment substrates needed for cellular metabolism. The function of these cells in absorption is reflected in the specialized structure of the cell surface, which is enormously increased by the presence of numerous microvilli forming a "brush border." Because of the specialized nature of the intestinal mucosal and kidney tubule cells, much data have come from the study... 

FIGURE 5.13 Two basic types of biological transport are (a) transport within or between different cells or tissues and (b) transport into or out of cells. Proteins function in both of these phenomena. For example, the protein hemoglobin transports oxygen from the lungs to actively respiring tissues. Transport proteins of the other type are localized in cellular membranes, where they function in the uptake of specific nutrients, such as glucose (shown here) and amino acids, or the export of metabolites and waste products. 

The processes of electron transport and oxidative phosphorylation are membrane-associated. Bacteria are the simplest life form, and bacterial cells typically consist of a single cellular compartment surrounded by a plasma membrane and a more rigid cell wall. In such a system, the conversion of energy from NADH and [FADHg] to the energy of ATP via electron transport and oxidative phosphorylation is carried out at (and across) the plasma membrane. In eukaryotic cells, electron transport and oxidative phosphorylation are localized in mitochondria, which are also the sites of TCA cycle activity and (as we shall see in Chapter 24) fatty acid oxidation. Mammalian cells contain from 800 to 2500 mitochondria other types of cells may have as few as one or two or as many as half a million mitochondria. Human erythrocytes, whose purpose is simply to transport oxygen to tissues, contain no mitochondria at all. The typical mitochondrion is about 0.5 0.3 microns in diameter and from 0.5 micron to several microns long its overall shape is sensitive to metabolic conditions in the cell. 

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