Transport primary active mechanism

Besides by interfering with the general energy maintenance of the cell, impact of active transport during intracellular accumulation can also be investigated by direct inhibition of certain transport mechanisms. To detect contribution of Na+-dependent transport, the Na+/K+-ATPase, one of the primary active transport systems of the cell, can be inhibited by ouabain at 10 /uM. Higher amounts of the inhibitor may seriously impede with the viability of the cell. To obtain reliable results, the cells are pretreated with ouabain for 15 min prior to addition of the analyte. Usually, the inhibitory effect of ouabain lasts up to 45 min [29],... 

Figure 9.29 Some mammalian (left) and microbial (right) membrane transport systems. (A) Primary electrogenic mechanisms (pumps) creating either a Na+ or a H+ gradient. (B) Secondary active transport systems of the symport type, in which the entry of a nutrient S into the cell is coupled with the entry of either the sodium ions or protons. (D) Various passive ion movements, possibly via channels or uniports. (Reproduced by permission from Serrano R. Plasma Membrane ATPase of Plants and Fungi. Boca Raton CRC Press, 1985, p. 59.)...

The transport of molecules across the plasma membrane of a cell occurs by three major mechanisms simple diffusion across the membrane, facilitated diffusion through channels or carriers, and active transport of molecules by carriers and pumps. The latter form of transport requires energy from the cell and is divided into two major types primary active and secondary active (1,2). 

Figure 10.1 Sites and mechanisms of action of diuretics. The location of each cell type along the nephron is indicated by the shading patterns. Spironoiactone (not shown) is a competitive aldosterone antagonist and acts primarily in the collecting duct. PT, proximal tubule LH, loop of Henie TAL, thick ascending limb DT, distal tubule DCT, distal convoluted tubule CD, collecting duct PC, principal cell CA, carbonic anhydrase CAI, carbonic anhydrase inhibitors , primary active transport. (Adapted with permission from Ellison D H 1991 The physiologic basis of diuretic synergism its role in treating diuretic resistance. Annals of Internal Medicine 114 886-894.)...

Figure 4S-6 Tubular reabsorptive mechanisms the major primary active transport processes in the proximal nephron.The renal tubular epithelium consists of a single layer of ceils. At the luminal side, adjacent cells are in contact (the tight junction), whereas toward the basal side of the cells, there are gaps between adjacent cells (lateral intercellular spaces). (From Lote CJ. Principles of renal pfiysio/ogy. 4tb ed. London Kluwer Academic Publishers, 2000 Chapter 4.)...

Direct coupling of adenosine triphosphate (ATP) hydrolysis is an example of an active transport process. The most important of these in the nephron is Nafi K -ATPase, which is located on the basolateral membranes of the tubulo-epithelial cells (Figure 45-6). This enzymatic transporter accounts for much of renal oxygen consumption and drives more than 99% of renal sodium reabsorption. Other examples of primary active transport mechanisms are a Ca " -ATPase, an H -ATPase, and an H, K -ATPase. These enzymes establish ionic gradients, polarizing cell membranes and thus driving secondary transport processes. 

The chemotaxis receptors for PTS carbohydrates are enzymes II [10]— membrane proteins that transport certain hexoses, hexosamines, polyhy-dric alcohols, and disaccharides [582, 602]. The mechanism of transport involves activation of enzyme II by phosphorylation, carried out by two cytoplasmic protein kinases enzyme I and histidine-containing protein (HPr) [582], Unlike the case of the periplasmic binding proteins, the PTS primary receptor—enzyme II—does not interact directly with an MCP As will be discussed in Section 8.2.7, it is enzyme I which links the occupancy of enzyme II with the chemotaxis system. 

This explains why there is no principal difference between the raw (doped) polyaniline and its dispersions, in whatever medium. The differences to be observed were only of quantitative, and not of qualitative nature, at least not in the direction, which was expected by most of those who still favor the fibril hypothesis. They believe that the chain is the primary active unit, which could also be dissolved and is believed to have conductive properties, even as a single chain. If that were the case, a dispersed (i.e., mechanically separated, in case of assumed fibrillar morphology, even destroyed) conductive polymer would not have the same conductivity and especially not the same transport properties in the dispersion medium above the critical volume concentration or after deposition from a low molecular weight liquid medium and drying. 

Thus far, differentiation of iPSCs to a mature HLC phenotype that is comparable to primary hepatocytes has proven to be challenging. HLCs generated in different studies appeared to be more fetal-like. Small molecules identified by high-throughput screening demonstrated their potential for HLC maturation (increased albumin secretion, CYP activity, and gene expression of ABC transporters), although the mechanisms are unclear (Bohme et al., 1994). 

Fig. 4. Schematic mechanism of a chemical model of primary active transport (reaction pumping).

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