Ion transport, membrane

X-ray diffraction studies on gramicidin commenced as early as 1949 218-219> and this early work pointed to a helical structure 220). Recent work by Koeppe et al. 221) on gramicidin A crystallised from methanol (/%) and ethanol (.P212121) has shown that the helical channel has a diameter of about 5 A and a length of about 32 A in both cases. The inclusion complexes of gramicidin A with CsSCN and KSCN (P212121) have channels that are wider (6-8 A) and shorter (26 A) than the uncomplexed dimer 221 222). Furthermore there are two cation binding sites per channel situated either 2.5 A from either end of the channel or 2.5 A on each side of its centre 222) Unfortunately these data do not permit a choice to be made from the helical models (i)—(iv) and it is not certain if the helical canals studied are the same as those involved in membrane ion transport. 

Cyclodiene pesticides, of which endrin and its oxidized analogs are representative, can also be estimated by receptor-assay technique. Cyclodiene pesticides exert their mode of action by altering central nervous system membrane ion transport. In work reported by Saleh et al. (1993), a labeled amino acid, GABA, that binds to the chloride channel receptor is displaced by endrin (and other similar molecules), and thus serves as an assay for these pesticides. The GABA receptor was shown to be a potentially useful biomarker for organochlorine pesticides such as lindane, toxaphene, endrin, chlordane, and others. The assay involves small quantities of blood (0.1 mL), and requires only that the plasma be separated from the... 

Stintzi A, Barnes C, Xu J, Raymond KN (2000) Microbial Iron Transport via a Siderophore Shuttle a Membrane Ion Transport Paradigm. Proc Natl Acad Sci USA 97 10691... 

Fig. 4.3 Uptake of glutamate is associated with ion transport across neural membranes. Ion transport results in entry of 3 sodium ions and 1 proton in the cell whilst 1 potassium ion is transported out (modified from Attwell, 2000)...

Among other actions, hormones are known to modify the activities of membrane ion transporters and ion channels, affect the membrane potential, and modulate Na+-driven substrate transport (for review see Moule and McGivan, 1990). These actions in turn are expected to modify cell volume. Thus, for example, hormones are now recognized as potent modulators of liver cell volume (Haussinger and Lang, 1992). Whereas anisoosmotic exposure and amino acid accumulation in hepatocytes primarily lead to cell swelling with secondary activation of volume-regulatory ion transporters, hormones primarily affect the activity of these volume-... 

Figure 4.1. Major membrane ion transport systems that shape the ion concentration gradients across the cytoplasmic membrane. Top Na /K -ATPase left NaTCa Nexchanger bottom Ion chaimels for and Na, and KTCf-cotransporter right Na -amino acid cotransporter.

Andrews P, Albright K. 1991. Role of membrane ion transport in cisplatin accumulation. Paper presented at the Platinum and other metal coordiantion compounds in cancer chemotherapy. 

Designer cyclopeptides for self-assembled tubular structures 00PAC365. Designer hybrid cyclopeptides for membrane ion transport and tubular structures 01ACR919. 

Its cellular functions comprise skeletal and cardiac muscle contraction cellular secretion exocrine, endocrine, and neurotransmitters, neural excitation and regulation of membrane ion transport enzyme regulation (gluconeogenesis and glycogenolysis) and cell growth and division. 

Jacobson, H.R., S. Corona, J.H. Capdevila, N. Chacos, S. Manna, A. Womack et al. (1984). Effects of epoxyeicosatrienoic acids on ion transport in the rabbit cortical collecting tubule. In P. Braquet, J.C. Frolich, S. Nicosia, and R. Garay (eds). Prostaglandins and Membrane Ion Transport. Raven Press, New York, p. 311. 

I. Mechanism of toxicity. In Insects, pyrethrins and pyrethroids rapidly cause death by paralyzing the nervous system through disruption of the membrane ion transport system in nerve axons, and pyrethroids prolong sodium influx and also... 

Halushka, P.V. and Burch, R.M. (1984). Effects of arachidonic acid metabolites on Ca fluxes and intracellular calcium in epithelial cells from the toad urinary bladder. In Braquet, P. et al. (eds.) Prostaglandin and Membrane Ion Transport, pp. 323-26. (New York Raven Press)... 

The specialty field of membrane ion transport studies is growing rapidly. It is, however, not the intent of this brief discussion to do more than touch on the subject of mechanisms by which electric fields control membrane transport. Rather, emphasis has been placed on describing the effects of electric fields on cells. At present, much of the research in this experimental field is Edisonian. However, the large body of experimental data that has accumulated strongly supports the hypothesis that ionic gradients are critically involved in the control of cell processes. That this is true can best be illustrated by the practical medical uses of electric fields to control or inhibit growth of tissue and bone. 

Furthermore there are two cation binding sites per channel situated either 2.5 A from either end of the channel or 2.5 A on each side of its centre Unfortunately these data do not permit a choice to be made from the helical models (i)-(iv) and it is not certain if the helical canals studied are the same as those involved in membrane ion transport. 

Reverse osmosis can be used for the separation of ions om an aqueous solution. Neutral membranes are mainly used for such processes and the transport of ions is determined by their solubility and diffusivity in the membrane (as expressed by the solute permeability coefficient, see eq V 162). The driving force for ion transport is the concentration difference, but if charged membranes or ion-exchange membranes are used instead of neutral membranes ion transport is also affected by the presence of the fixed charge. Teoreil [45] and Meyer and Sievers [46] have used a fixed charge theory to describe ionic transport through these type of systems. This theory is based on two principles the Nemst-Planck equation and Dorman equilibrium. 

Figure 7.4 Typical potential energy ion barriers postulated for membrane ion transport.

In a second example, biotinylated MCM-41 was incorporated into lipid bilayer membranes. Ion transport through the membrane was controlled by the binding of avidin. Since the assembly of the MCM particles in the membrane is random, maximum blockage rates of 80% could only be achieved. As a clear conttast, addition of bovine serum... 

Membrane potential (MP) gives information on the effective fixed charge associated with the bulk membrane phase, Dorman equilibrium between the membrane, and the adjacent solution, and the relative flow of ion through the membrane (ion transport number). 

Ranganathan, D., Samant, M.R, Nagaraj, R., and Bikshapathy, E. Design, synthesis and membrane ion transport properties of cystine- and serine-based cyclo-4-oxa-heptane-l,7-bisamides. Tetrahedron Lett 2002,43 5145-5147. 

Ranganathan, D., Haridas,V., Kurur, S., Nagaraj, R., Bikshapathy, E., Kunwar, A.C., Sarma, A.V., and Vairamani, M. Norbomene-constrained cyclic peptides with hairpin architecture design, synthesis, conformation, and membrane ion transport. J Organic Chem 2000, 65 365-374. 

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