Electrogenic ion transport

Cooke, H J., Wang, Y.Z., 1994. H3 receptors Modulation of histamine-stimulated neural pathways influencing electrogenic ion transport in the guinea pig colon. J. Auton Nerv. Syst. 50, 201-207. 

Electric field effects play an important role in many biological cell processes. Phenomena as different as nerve excitation, electrogenic ion transport, neurostimulated secretion of hormones and transmitter substances, or the photosynthesis of involve cell functions in which... 

Figure 2. Sodium and chloride uptake across an idealised freshwater-adapted gill epithelium (chloride cell), which has the typical characteristics of ion-transporting epithelia in eukaryotes. In the example, the abundance of fixed negative charges (muco-proteins) in the unstirred layer may generate a Donnan potential (mucus positive with respect to the water) which is a major part of the net transepithelial potential (serosal positive with respect to water). Mucus also contains carbonic anhydrase (CA) which facilitates dissipation of the [H+] and [HCO(] to CO2, thus maintaining the concentration gradients for these counter ions which partly contribute to Na+ import (secondary transport), whilst the main driving force is derived from the electrogenic sodium pump (see the text for details). Large arrow indicates water flow...

Figure 15.2 Ion transporters in human vaginal-ectocervical epithelial cells, sorted into the apical and basolateral domains of the plasma membrane. Black solid symbols depict electrogenic transporters hatched symbols depict electroneutral transporters. Squares are tight junctions. MCT—monocarboxylate transporter NBC— Na+/HCO co-transporter AE—acid (Cl /HCOj ) exchanger NHE (types 1 or 3)—Na+/H+ exchangers.

OTEIER EPITEIEUA Electrogenic and electroneutral ion transporters and their regulation in tracheal epithelium, 192, 549 transformation of airway epithelial cells with persistence of cystic fibrosis or normal ion transport phenotypes, 192, 565 cell culture of bovine corneal endothelial cells and its application to transport studies, 192, 571 methods for studying eccrine sweet gland function in vivo and in vitro, 192, 583. 

Most studies of the local actions of opioids on the intestinal mucosa have utilized muscle-stripped sheets of ileal mucosa with attached submucosa mounted in Ussing flux chambers. Peptidase-resistant enkephalin derivatives such as DPDPE decrease short-circuit current, an electrical measure of active transepithelial ion transport, across isolated mucosal sheets from the guinea pig ileum [46,127,128], rabbit ileum [129-131], mouse jejunum [132], and pig distal jejunum/ileum [133]. This effect, which occurs after the application of opioid agonists to the serosal aspect of epithelial sheets, is due to an increase in electroneutral salt absorption and a decrease in electrogenic chloride secretion [46,132,133], In contrast to enkephalin derivatives, opiate alkaloids have limited effects on active transepithelial transport of ions [69]. Pretreat-... 

Net reaction between hydrophilic oxidants and reductants separated by bilayer membranes has been convincingly demonstrated in numerous asymmetrically organized vesicle and planar bilayer systems [2a-c]. Particularly compelling examples are those in which electrogenic electron transport is accompanied by net translocation of lipophilic cations or anions, as is required to maintain electroneutrality. For example, MV + occluded within the inner aqueous phase of DHP vesicles can be completely reduced to the MV+ radical cation by 8204 ion in the bulk phase, but only if an equal or greater amount of viologen is initially present in the external environment [40]. Neither MV-+ nor 8204 is membrane permeable. The reaction is biphasic, with rapid bimolecular reduction of external being followed by... 

The mechanism by which the exergonic methyl-transfer reaction is coupled with vectorial electrogenic Na translocation across the membrane is not known. An electron transport chain appears not to be involved in Na transport. Sodium ion transport... 

Ussing chamber measurements are the most commonly used method to investigate transepithelial ion transport [164, 165], They can be performed on either functional epithelia from biopsies or on cultivated epithelia. The Ussing chamber itself is more or less a U-shaped chamber, which is compartmentalized by an epithelial cell layer and solute flux between both compartments can be measured. Electrogenic ion fluxes can be measured directly by short circuit measurements or calculated from open circuit measurements [165], Non-electrogenic solute flux needs continuous concentration measurements for each compartment separately [166]. Thus, Ussing chamber experiments enable to study permeation kinetics for secretion and resorption separately [166-169] and to evaluate effects on ion transport pathways [85, 87, 90, 170]. 

Mutations in the Saccharomyces cerevisiae H+-ATPase gene, PMA1, that confer cellular growth resistance to hygromycin B cause a generalized depolarization of cellular membrane potential. The normal hyperpolarized membrane potential in yeast is maintained by the H+-ATPase, and it is believed that the pmal mutations alter electrogenic proton transport by the enzyme. Electroneutral H+ transport by the mutant enzymes may involve the countertransport of K+, but other ions including H+ could participate. More direct evidence is needed to confirm the role of K+ as a counterion and to probe its putative transport mechanism. It will be important to determine whether H + and K+ use the same mechanistic pathway for transport. 

Heinz, E., "Electrogenic and Electrically Silent Proton Pumps in Hydrogen Ion Transport in Epithelia" Shultz, I, Sachs, G.,... 

The electrogenic ion pump in the plasma membrane of animal cells is the Na+/K+-ATPase. As shown in Fig. 12, three Na+ ions are transported out of the cell and two K+ ions are pumped in for each ATP that is hydrolyzed. Since three positively charged ions are exported, but only two imported, the Na+/K+-ATPase is electrogenic. The trans... 

Such considerations have led us to adopt a less restrictive modellistic approach . For the diagnostic of steady state electrogenic ion transfer, we have used therefore a computation which starts from the Nernst-Planck equation, avoids a separation between diffusion and ion pumping, both appearing at once as antagonistic and complementary processes (see Equation 6), and which handles all transferable chemical species possibly involved in ion transfer across membrane without selecting a priori a main transport process. 

Neurotransmitter transport can be electrogenic if it results in the net translocation of electrical charge (e.g. if more cations than anions are transferred into the cell interior). Moreover, some transporters may direction-ally conduct ions in a manner akin to ligand-gated ion channels this ion flux is not coupled to substrate transport and requires a separate permeation pathway associated with the transporter molecule. In the case of the monoamine transporters (DAT, NET, SERT) the sodium current triggered by amphetamine, a monoamine and psychostimulant (see Fig. 4) is considered responsible for a high internal sodium concentration... 

From the point of view of the stoichiometry of the transported ions during active transport, the electroneutral pump, where there is no net charge transfer or change in the membrane potential, must be distinguished from the electrogenic pump connected with charge transfer. 

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