Transporter reversal

PXR CAR FXR LXR AhR 3A4 and others 2B, 2C, 3A4 7A 7A 1A1, 1A2, 1A6, 1B1, 2S1 Xenobiotic metabolism regulation, antioxidant Xenobiotic metabolism regulation Bile add metabolism and transport Reverse cholesterol transport and absorption Reproduction and development regulation... 

Classical neurotransmitters and monoamines may rarely be secreted by neurons, not by exocytosis, but by transporter reversal. This mechanism involves the transport of neurotransmitters from the cytosol to the extracellular fluid via transporters that normally remove neurotransmitters from the extracellular fluid. This mechanism appears to account for the burst of dopamine released by amphetamines (Fleckenstein et al., 2007), but its physiological occurrence remains unclear. 

Raiteri, L., Stigliani, S., Patti, L., Usai, C., Bucci, G., Diaspro, A, Raiteri, M., and Bonanno, G. (2005a). Activation of GABA GAT-1 transporters on glutamatergic terminals of mouse spinal cord mediates glutamate release through anion channels and by transporter reversal. J. Neurosci. Res. 80, 424-433. 

Phillis, J. W., Ren, J., and O Regan, M. H. (2000). Transporter reversal as a mechanism of glutamate release from the ischemic rat cerebral cortex Studies with DL-threo-b-benzyloxyaspartate. Brain Res. 868, 105-112. 

Elken, J., Raudsepp, U., Lips, U., 2003. On the estuarine transport reversal in deeplayers of the Gulf of Finland. Journal of Sea Research, 49, 267-274. 

C. Potassium depletion resulting in a 1-mEq/L decrease in serum potassium may require 100-200 mEq tor replacement to restore body stores. This replacement requirement will be offset with changes or corrections in intracellular transport (reversal of methyixanthine or beta-adrenergic agonist toxicity). 

Reversed electron transport reversal of Oxidative phosphorylation (see) in which NAD is reduced by an ATP-dependent reverse transport of electrons. R.e.t. occurs in organisms that oxidize hydrogen donors whose redox potential (see Oxidation) is more positive than that of the pjmdine nucleotide coenzymes, and it operates in the oxidation of substrates not specific for NAD (see Respiratory chain), e.g. Succinate + NAD - Fumate + NADH + H. Tlie redox system succinate/fumarate (E o = -tO - 031V) is 325 mV more positive than the redox system NAJD / NADH + H (E o =-0.32 V) electrons are passed firom succinate to flavoprotein in the respiratory chain, then via NADH-dehydrogenase to NAD. R.e.t. has been shown in nitrate bacteria (Nitrobac-ter), insect flight muscle mitochondria and kidney mi-... 

The use of the first and the second laws of thermodynamics allows a simple description of a reversible fuel cell. The fuel and the air enter the fuel cell as non-mixed flows of the different components and the flue gas leaves the fuel cell as a non-mixed flow as well if we assume a reversible operating fuel cell. The non-mixed reactants deliver the total enthalpy EnjHi to the fuel cell and the total enthalpy leaves the cell with the non-mixed products. Furthermore the heat Qpcrev must be extracted reversibly from the fuel cell and transported reversibly to the environment. This can be done, for example, if the fuel cell and the environment have the same thermodynamic state. Qpcrcv is defined as a positive number if it is transported to the fuel cell. The reversible work - W pcrev is delivered by the fuel cell. An idealised description of this model is given in Figure 3.1. 

As also noted in the preceding chapter, it is customary to divide adsorption into two broad classes, namely, physical adsorption and chemisorption. Physical adsorption equilibrium is very rapid in attainment (except when limited by mass transport rates in the gas phase or within a porous adsorbent) and is reversible, the adsorbate being removable without change by lowering the pressure (there may be hysteresis in the case of a porous solid). It is supposed that this type of adsorption occurs as a result of the same type of relatively nonspecific intermolecular forces that are responsible for the condensation of a vapor to a liquid, and in physical adsorption the heat of adsorption should be in the range of heats of condensation. Physical adsorption is usually important only for gases below their critical temperature, that is, for vapors. 

The effects of ultrasound-enlianced mass transport have been investigated by several authors [73, 74, 75 and 76]. Empirically, it was found that, in the presence of ultrasound, the limiting current for a simple reversible electrode reaction exhibits quasi-steady-state characteristics with intensities considerably higher in magnitude compared to the peak current of the response obtained under silent conditions. The current density can be... 

The bipolar junction transistor (BIT) consists of tliree layers doped n-p-n or p-n-p tliat constitute tire emitter, base and collector, respectively. This stmcture can be considered as two back-to-back p-n junctions. Under nonnal operation, tire emitter-base junction is forward biased to inject minority carriers into tire base region. For example, tire n type emitter injects electrons into a p type base. The electrons in tire base, now minority carriers, diffuse tlirough tire base layer. The base-collector junction is reverse biased and its electric field sweeps tire carriers diffusing tlirough tlie base into tlie collector. The BIT operates by transport of minority carriers, but botli electrons and holes contribute to tlie overall current. 

Kulak L and Bo]arski C 1995 Forward and reverse eleotronio-energy transport and trapping in solution 1. Theory Chem. Phys. 191 43-66... 

The ready reversibility of this reaction is essential to the role that qumones play in cellular respiration the process by which an organism uses molecular oxygen to convert Its food to carbon dioxide water and energy Electrons are not transferred directly from the substrate molecule to oxygen but instead are transferred by way of an electron trans port chain involving a succession of oxidation-reduction reactions A key component of this electron transport chain is the substance known as ubiquinone or coenzyme Q... 

Influence of the Kinetics of Electron Transfer on the Faradaic Current The rate of mass transport is one factor influencing the current in a voltammetric experiment. The ease with which electrons are transferred between the electrode and the reactants and products in solution also affects the current. When electron transfer kinetics are fast, the redox reaction is at equilibrium, and the concentrations of reactants and products at the electrode are those specified by the Nernst equation. Such systems are considered electrochemically reversible. In other systems, when electron transfer kinetics are sufficiently slow, the concentration of reactants and products at the electrode surface, and thus the current, differ from that predicted by the Nernst equation. In this case the system is electrochemically irreversible. 

Off-gases (top gas) leave the top of the furnace through uptake pipes, reverse direction ia the downcomer, and enter the dust catcher, ia which condensed water and dust are separated from the gases. The wet dust is emptied iato a rail car for transport to a siater plant for recycle or to a landfill. 

Nonporous Dense Membranes. Nonporous, dense membranes consist of a dense film through which permeants are transported by diffusion under the driving force of a pressure, concentration, or electrical potential gradient. The separation of various components of a solution is related directiy to their relative transport rate within the membrane, which is determined by their diffusivity and solubiUty ia the membrane material. An important property of nonporous, dense membranes is that even permeants of similar size may be separated when their concentration ia the membrane material (ie, their solubiUty) differs significantly. Most gas separation, pervaporation, and reverse osmosis membranes use dense membranes to perform the separation. However, these membranes usually have an asymmetric stmcture to improve the flux. 

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