Uptake by cells

Nickel is required by plants when urea is the source of nitrogen (Price and Morel, 1991). Bicarbonate uptake by cells may be limited by Zn as HCOT transport involves the zinc metal-loenzyme carbonic anhydrase (Morel et al., 1994). Cadmium is not known to be required by organisms but because it can substitute for Zn in some metalloenzymes it can promote the growth of Zn-limited phytoplankton (Price and Morel, 1990). Cobalt can also substitute for Zn but less efficiently than Cd. 

Data about curcunfin encapsulated in liposomes have been reported recently. The authors encapsulated curcumin into a liposomal delivery system in order to study the in vitro and in vivo effects of this compound on proliferation, apoptosis, signaling, and angiogenesis using human pancreatic carcinoma cells. Carotenoids of different polarities and in competition with cholesterol were specifically incorporated into liposomes in order to mimic the physiological uptake by cells and monitor their antioxidant capacities. ... 

Davies, N. A., Taylor, M. G. and Simkiss, K. (1997). The influence of particle surface characteristics on pollutant metal uptake by cells, Environ. Poll., 96, 179-184. 

In patients clearance of intravenous heme is rapid until hemopexin levels are depleted (148), and lack of interaction with hemopexin may explain the higher clinical efficacy of heme-arginate compared with hemin itself (149, 150). In intact animals, i.v. heme causes rapid association of hemopexin but not albumin with the liver (47, 63, 68), and heme uptake from heme-albumin complexes into isolated rat hepato-cytes occurs via diffusion of heme released from its loose complex with BSA (137). Moreover, unlike uptake from heme-hemopexin, free heme uptake by cells occurred even at 4°C, as expected for nonspecific membrane association and in total disagreement with a membrane-receptor-mediated or active transport uptake process. 

We begin with an account of the main steps in the biosynthesis of cholesterol from acetate, then discuss the transport of cholesterol in the blood, its uptake by cells, the normal regulation of cholesterol synthesis, and its regulation in those with defects in cholesterol uptake or transport. We next consider other cellular components derived from cholesterol, such as bile acids and steroid hormones. Finally, an outline of the biosynthetic pathways to some of the many compounds derived from isoprene units, which share early steps with the pathway to cholesterol, illustrates the extraordinary versatility of isoprenoid condensations in biosynthesis. 

One of the most important effects of insulin is to increase glucose uptake by cells 373/389 The mechanism is thought to depend upon the transporter protein GLUT4, which is stored within the membranes of small cytoplasmic vesicles. Binding of insulin to its receptors induces movement of these vesicles to the plasma membrane where fusion with the plasma membrane makes the GLUT4 molecules available for glucose transport.390 Phosphatidylinositol 3-kinase also plays an important role. The PtdIns(3,4)P2 and PtdIns(3,4,5)P3 generated by this enzyme (Fig. 11-9)... 

In this study, a LOQ of 20 pg/mL in cell lysates would be needed in order to quantify paclitaxel uptake by cells exposed to approx. 1 ng/mL drug, but the detection limits of published LC-MS/MS based methods were in the range of 0.1-0.25 ng/mL [10,15-21], Furthermore, concentrations of paclitaxel lower than 1 ng/mL are pharmacologically active, and therefore, a LOQ lower than 20 pg/mL is desirable. 

A121a cells were exposed to paclitaxel at concentrations of 0.2, 0.8, 2, and 5 ng/mL. Paclitaxel uptake by cells was able to be quantified at each time point under four treatment conditions. The lowest measured intracellular accumulation was 6.5 pg/106 cells, observed 10 min after the addition of 0.2 ng/mL paclitaxel to cells. The detected concentration in this sample corresponded to approximately 9.6 pg/mL drug in the cell lysate, which is nearly twice the LOQ. Foremost concentrations of paclitaxel, it appeared that the intracellular drug concentrations increased rapidly with exposure time and reached a plateau within 1-3 h. However, for cells exposed to the lowest concentration (0.2 ng/mL), the maximum intracellular drug concentration apparently was not achieved within 6 h, which was longest time interval investigated. In future studies, these data will be expanded to include additional concentrations and exposure times, and analyzed according to cellular pharmacokinetic models such as those published previously [12],... 

Transport is inhibited by phlorhizin directly and indirectly by stopping the Na/K pump. Ouabain is an inhibitor of the latter. Because gramicidin is a Na+/ K+ ionophore, it short-circuits the Na+ gradient and may thus inhibit glucose uptake by cells. 

Both IDL and LDL can be removed from the circulation by the liver, which contains receptors for ApoE (IDL) and ApoB-100 (IDL and LDL). After IDL or LDL interacts with these receptors, they are internalized by the process of receptor-mediated endocytosis. Receptors for ApoB-100 are also present in peripheral tissues, so that clearance of LDL occurs one-half by the liver and one-half by other tissues. In the liver or other cells, LDL is degraded to cholesterol esters and its other component parts. Cholesterol esters are hydrolyzed by an acid lipase and may be used for cellular needs, such as the building of plasma membranes or bile salt synthesis, or they may be stored as such. Esterification of intracellular cholesterol by fatty acids is carried out by acyl-CoA-cholesterol acyltransferase (ACAT). Free cholesterol derived from LDL inhibits the biosynthesis of endogenous cholesterol. B-100 receptors are regulated by endogenous cholesterol levels. The higher the latter, the fewer ApoB-100 receptors are on the cell surface, and the less LDL uptake by cells takes place. 

PolyPs are the principal regulators of the intracellular level of P in microorganisms. In all cases of rapid P uptake by cells, when the pathways of its utilization are limited, PolyPs are accumulated and the intracellular concentration of P remains low (Harold, 1966 ... 

One of the most widely used treatments for breast cancer uses tamoxifen (Figure 14.8). It was originally developed as a contraceptive, but it was found that it inhibited oestrogen uptake by cells. Tamoxifen alters the shape of a protein on the surface of the oestrogen receptor and so stops it from giving the signal to grow . 

Carbon monoxide is a toxic gas that binds hemoglobin more efficiently than dioxygen, and therefore its presence decreases the oxygen uptake by cells, ultimately leading to asphyxia. 

Blaner WS, Obunike JC, Kurlandsky SB, al-Haideri M, Piantedosi R, Deckelbaum RJ, and Goldberg IJ (1994) Lipoprotein lipase hydrolysis of retinyl ester. Possible implications for retinoid uptake by cells. Journal of Biological Chemistry 269,16559-65. 

Templeton DM. Cadmium uptake by cells of renal origin. J Biol Chem 1990 265 21764-21770. 

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