Transportation responsibilities

M (blockage of calcium intestinal transport response to vitamin D)... 

There are several factors which may be responsible for the variability in the uptake of different carotenoids. These include differences in the distribution of carotenoids among serum lipoproteins and differences in the expression on cell membranes of the various receptors/transporters responsible for uptake of different types of lipoproteins. It may be further expected that the efficiencies for uptake of different carotenoids may vary for different types of receptors/transporters. Also, the further processing of internalized different carotenoids may vary. 

Carayannopoulos, M. O., et al. GLUT8 is a glucose transporter responsible for insulin-stimulated glucose uptake in the blastocyst. Proc. Natl. Acad. Sci. U. S. A. 2000, 97, 7313-7318. 

Tang, F., Borchardt, R. T., Characterization of the efflux transporters) responsible for restricting intestinal mucosa permeation of the coumarinic acid-based cyclic prodrag of the opioid peptide DADLE, Pharm. Res. 2002, 19, 787-793. 

Monoamine reuptake inhibitors elevate extracellular levels of serotonin (5-HT), norepinephrine (NE) and/or dopamine (DA) in the brain by binding to one or more of the transporters responsible for reuptake, namely the serotonin transporter (SERT), the norepinephrine transporter (NET) and the dopamine transporter (DAT), thereby blocking the reuptake of the neurotransmitter(s) from the synaptic cleft [1], Monoamine reuptake inhibitors are an established drug class that has proven utility for the treatment of a number of CNS disorders, especially major depressive disorder (MDD). 

Development of predictive models through better understanding of the mechanisms of mass transport responsible for the water removal and... 

Many drugs have been recognized to cross the intestinal epithelial cells via passive diffusion, thus their lipophilicity has been considered important. However, as described above, recent studies have demonstrated that a number of drug transporters including uptake and efflux systems determine the membrane transport process. In this chapter, we provide an overview of the basic characteristics of major drug transporters responsible not only for absorption but also for disposition and excretion in order to delineate the impact of drug transport proteins on pharmacokinetics. 

The answer is D. The patient s symptoms are consistent with a kidney stone, which is confirmed by the radiographic finding. The etiology of the stone is indicated by the urinalysis data, which suggest cystinuria. The cells of this patient s renal proximal tubules would be deficient in a transporter responsible for the reabsorptive uptake of cystine and the basic amino acids, arginine, lysine, and ornithine. Failure of the tubules to reabsorb these amino acids from the ultrafiltrate causes them to be excreted at high concentration in the urine. 

NET, SLC6A2, the norepinephrine transporter, is a member of the SLC family, as are similar transporters responsible for the reuptake of dopamine (DAT, SLC6A3) and 5-HT (serotonin, SERT, SLC6A4) into the neurons that release these transmitters. These transport proteins are found in peripheral tissues and in the CNS wherever neurons utilizing these transmitters are located. 

Resistance Nonproliferating cells are resistant to methotrexate. Resistance in neoplastic cells can be due to amplification (production of additional copies) of the gene that codes for dihydrofolate reductase resulting in increased levels of this enzyme. The enzyme affinity for MTX may also be diminished. Resistance can also occur from a reduced influx of MTX, apparently caused by a change in the carrier-mediated transport responsible for pumping methotrexate into the cell. 

PURPOSE AND RATIONALE Once a compound is identified in an efflux assays it is sometimes of importance to discriminate between efflux, inhibition potential and to determine the efflux transporter responsible for efflux of the compound. 

Many fractions of red and green paprika extracts had reversed the MDR of cancer cells [13,16] in our previous experiments. The effectiveness of hexane and acetone fractions of paprika on the ABC transporter responsible for MDR reversal, made it worth studying the effects of carotenoids and flavonoids on the drug accumulation of cancer cells. 

Nakano, S., Fukaya, M., and Horinouchi, S. 2006. Putative ABC transporter responsible for acetic acid resistance in Acetobacter aceti. Applied and Environmental Microbiology 72 497-505. 

Table 17.2 lists the 43 molecules used in this study that are known to be substrates for active transport or active efflux. The mechanistic ACAT model was modified to accommodate saturable uptake and efflux by using standard Michaelis-Menten equations. It was assumed that transporters responsible for active uptake of dmg molecules from the lumen and active efflux from the enterocytes to the lumen were homogeneously dispersed within each luminal compartment and each corresponding enterocyte compartment, respectively. Equation 17.5 represents the... 

Sullivan, D.J., and Coleman, D.C. (1998) Identification and expression of multidrug transporters responsible for fluconazole resistance in Candida duhliniensis. Antimicrobial Agents and Chemotherapy, 42. 1819—1830. 

Sun H, Molday RS, Nathans J. 1999. Retinal stimulates ATP hydrolysis by purified and reconstituted ABCR, the photoreceptor-specific ATP-binding cassette transporter responsible for Stargardt disease. J Biol Chem 274 8269-8281. 

Receptors and transporters (responsible for reuptake of neurotransmitters see below) are the main target for drag action. 

Fgut is the fraction of drug absorbed into the enterocytes that escapes presystemic intestinal elimination. It is the fraction delivered into the portal vein after gut first pass. Compounds with significant gut first pass tend to have high exposure variability since the enzymes or transporters responsible for the first pass could be induced, inhibited, or saturated at different extent among individuals [11], Therefore, this undesired property should be screened out in the lead optimization stage. 

---