Carrier-mediated ion transport in lipid bilayer membranes

1984 ◽  
Vol 62 (8) ◽  
pp. 738-751 ◽  
Author(s):  
Raynald Laprade ◽  
François Grenier ◽  
Monique Pagé-Dansereau ◽  
Janine Dansereau
Keyword(s):  
Steady State ◽  
Ion Transport ◽  
Lipid Bilayers ◽  
Aqueous Phase ◽  
Rate Constants ◽  
The Other ◽  
Electrostatic Energy ◽  
Membrane Thickness ◽  
Lipid Bilayer Membranes ◽  
Electrical Measurements

The electrical properties predicted by a widely accepted model for carrier-mediated ion transport in lipid bilayers are described. The different steps leading to ion transport and their associated rate constants are reaction at the interface between an ion in the aqueous phase and a carrier in the membrane (kRi), followed by translocation of the ion–carrier complex across the membrane interior (kis) and its dissociation at the other interface (kDi) after which the free carrier crosses back the membrane interior (ks). Results on glyceryl monooleate (GMO) membranes for a family of homologue carriers, the macrotetralide actin antibiotics (nonactin, monactin, dinactin, trinactin, and tetranactin) and a variety of ions (Na+, Cs+, Rb+, K+, NH4+, and Tl+) are presented. Internally consistent data obtained from steady-state electrical measurements (zero-current potential and conductance, current-voltage relationship) allow us to obtain the equilibrium permeability ratios for the different ions and show that for a given carrier kRi is relatively invariant from one ion to the other, except for Tl+ (larger), which implies that the ionic selectivity is controlled by the dissociation of the complex. The values of the individual rate constants obtained from current relaxation experiments are also presented and confirm the findings from steady-state measurements, as well as the isostericity concept for complexes of different ions with the same carrier (kis invariant). These also allow us to determine the aqueous phase membrane and torus membrane partition coefficients. Finally, the observed increase in kis from nonactin to tetranactin and, for all homologues, from GMO–decane to solvent-free GMO membranes, together with the concomitant decrease in kDi, can be explained in terms of modifications of electrostatic energy profiles induced by variations in carrier size and membrane thickness.

scholarly journals Ion Transport Through Excitability-Inducing Material (EIM) Channels in Lipid Bilayer Membranes

1972 ◽  
Vol 60 (1) ◽  
pp. 72-85 ◽  
Author(s):  
Ramon Latorre ◽  
Gerald Ehrenstein ◽  
Harold Lecar
Keyword(s):  
Aqueous Solution ◽  
Ion Transport ◽  
Lipid Bilayers ◽  
Voltage Dependence ◽  
The Other ◽  
Lipid Bilayer Membranes ◽  
Relative Permeabilities ◽  
Bilayer Membranes ◽  
Voltage Dependent ◽  
Ionic Mobilities

Two different methods were used to determine the relative permeability and the voltage-dependent conductance of several different cations in excitability-inducing material (EIM)-doped lipid bilayers. In one method, the conductances of individual channels were measured for Li, Na, K, Cs, NH4, and Ca, and in the other method biionic potentials of a membrane with many channels were measured for Li, Na, K, Cs, and Rb. The experimental results for the two methods are in agreement. The relative permeabilities are proportional to the ionic mobilities in free aqueous solution. The voltage dependence of the conductance is the same for all cations measured.

Effects of variation of ion and methylation of carrier on the rate constants of macrotetralide-mediated ion transport in lipid bilayers

1982 ◽  
Vol 68 (1) ◽  
pp. 191-206 ◽  
Author(s):  
Raynald Laprade ◽  
François Grenier ◽  
Jean-Yves Lapointe ◽  
Sylvic Asselin
Keyword(s):  
Ion Transport ◽  
Lipid Bilayers ◽  
Rate Constants

scholarly journals Kinetic characteristics of the excitability-inducing material channel in oxidized cholesterol and brain lipid bilayer membranes.

1975 ◽  
Vol 65 (4) ◽  
pp. 421-439 ◽  
Author(s):  
O Alvarez ◽  
R Latorre ◽  
P Verdugo
Keyword(s):  
Steady State ◽  
Lipid Bilayers ◽  
Single Channel ◽  
Ionic Current ◽  
Brain Lipid ◽  
Kinetic Characteristics ◽  
Lipid Bilayer Membranes ◽  
Oxidized Cholesterol ◽  
Ion Conducting ◽  
Opening And Closing

The kinetic characteristics of the opening and closing of the excitability-inducing material (EIM) channel in oxidized cholesterol and in brain lipid bilayers are compared. The kinetics of the opening and closing of individual ion-conducting channels in bilayers doped with small amounts of EIM are determined from discrete fluctuations in ionic current. The kinetics for approach to steady-state conductance are determined for lipid bilayers containing many channels. Steady-state and kinetic characteristics for the EIM channel incorporated in brain lipid bilayers can be accounted for by the model developed for the EIM channel incorporated in oxidized cholesterol membranes. Relaxation time, calculated from rate constants of single-channel membranes or directly measured in many-channel membranes is strongly temperature dependent, and is always shorter in brain lipid membranes. Changes in temperature do not affect the interaction of the electric field and the open channel, but the open configuration of the EIM channel in brain lipid bilayers is stablized with increasing temperature. The configurational energy difference between the open and closed channel, calculated from temperature studies, is larger in brain lipid bilayers. The energy barrier which separates the two configurations of the channel is larger in oxidized cholesterol bilayers.

Fidelity of J1269 and J24523

2007 ◽  
Vol 35 (2) ◽  
pp. 94-117 ◽  
Author(s):  
James A. Popio ◽  
John R. Luchini
Keyword(s):  
Steady State ◽  
Rolling Resistance ◽  
Test Methods ◽  
The Other ◽  
Reference Condition ◽  
Test Standards

Abstract This study compares data from the two Society of Automotive Engineers test methods for rolling resistance: J-2452 (Stepwise Coast-Down) and J-1269 (Equilibrium) steady state. The ability of the two methods to evaluate tires was examined by collecting data for 12 tires. The data were analyzed and the data showed that the two methods ranked the tires the same after the data were regressed and the rolling resistance magnitude was calculated at the Standard Reference Condition. In addition, analysis of the two methods using this matched set of testing provided an opportunity to evaluate each of these test standards against the other. It was observed that each test has merits absent from the other.

scholarly journals Receptor-operated Ca2+ channels in gastric parietal cells: gastrin and carbachol induce Ca2+ influx in depleting intracellular Ca2+ stores

1993 ◽  
Vol 289 (1) ◽  
pp. 117-124 ◽  
Author(s):  
S Roche ◽  
J P Bali ◽  
R Magous
Keyword(s):  
Steady State ◽  
Receptor Activation ◽  
Parietal Cells ◽  
The Other ◽  
Bivalent Cation ◽  
Gtp Binding ◽  
Gastric Parietal Cells ◽  
Type Receptor ◽  
Ca2 Channels ◽  
Stimulation Of

The mechanism whereby gastrin-type receptor and muscarinic M3-type receptor regulate free intracellular Ca2+ concentration ([Ca2+]i) was studied in rabbit gastric parietal cells stimulated by either gastrin or carbachol. Both agonists induced a biphasic [Ca2+]i response: a transient [Ca2+]i rise, followed by a sustained steady state depending on extracellular Ca2+. Gastrin and carbachol also caused a rapid and transient increase in Mn2+ influx (a tracer for bivalent-cation entry). Pre-stimulation of cells with one agonist drastically decreased both [Ca2+]i increase and Mn2+ influx induced by the other. Neither diltiazem nor pertussistoxin treatment had any effect on agonist-stimulated Mn2+ entry. Thapsigargin, a Ca(2+)-pump inhibitor, induced a biphasic [Ca2+]i increase, and enhanced the rate of Mn2+ entry. Preincubation of cells with thapsigargin inhibits the [Ca2+]i increase as well as Mn2+ entry stimulated by gastrin or by carbachol. Thapsigargin induced a weak but significant increase in Ins(1,4,5)P3 content, but this agent had no effect on the agonist-evoked Ins(1,4,5)P3 response. In permeabilized parietal cells, Ins(1,4,5)P3 and caffeine caused an immediate Ca2+ release from intracellular pools, followed by a reloading of Ca2+ pools which can be prevented in the presence of thapsigargin. We conclude that (i) gastrin and carbachol mobilize common Ca2+ intracellular stores, (ii) Ca2+ permeability secondary to receptor activation involves neither a voltage-sensitive Ca2+ channel nor a GTP-binding protein from the G1 family, and (iii) agonists regulate common Ca2+ channels in depleting intracellular Ca2+ stores.

Methylene. III. Gas phase reactions with 1-chloropropane

1969 ◽  
Vol 312 (1509) ◽  
pp. 141-161 ◽  
Keyword(s):  
Gas Phase ◽  
Rate Constants ◽  
Hydrogen Abstraction ◽  
The Other ◽  
Gas Phase Reactions ◽  
Other Hand ◽  
Chlorine Substituent ◽  
High Degree ◽  
Singlet Methylene

The work described in this and the following paper is a continuation of that in parts I and II, devoted to elucidation of the mechanism of the reactions of methylene with chloroalkanes, with particular reference to the reactivities of singlet and triplet methylene in abstraction and insertion processes. The products of the reaction between methylene, prepared by the photolysis of ketene, and 1-chloropropane have been identified and estimated and their dependence on reactant pressures, photolysing wavelength and presence of foreign gases (oxygen and carbon mon­oxide) has been investigated. Both insertion and abstraction mechanisms contribute significantly to the over-all reaction, insertion being relatively much more important than with chloroethane. This type of process appears to be confined to singlet methylene. If, as seems likely, there is no insertion into C—Cl bonds under our conditions (see part IV), insertion into C2—H and C3—H bonds occurs in statistical ratio, approximately. On the other hand, the chlorine substituent reduces the probability of insertion into C—H bonds in its vicinity. As in the chloroethane system, both species of methylene show a high degree of selectivity in their abstraction reactions. We find that k S Cl / k S H >7.7, k T Cl / k T H < 0.14, where the k ’s are rate constants for abstraction, and the super- and subscripts indicate the species of methylene and the type of atom abstracted, respectively. Triplet methylene is discriminating in hydrogen abstraction from 1-C 3 H 7 Cl, the overall rates for atoms attached to C1, C2, C3 being in the ratios 2.63:1:0.

POVERTY TRAPS AND INFERIOR GOODS IN A DYNAMIC HECKSCHER–OHLIN MODEL

2012 ◽  
Vol 17 (6) ◽  
pp. 1227-1251 ◽  
Author(s):  
Eric W. Bond ◽  
Kazumichi Iwasa ◽  
Kazuo Nishimura
Keyword(s):  
Economic Theory ◽  
Steady State ◽  
World Economy ◽  
Steady States ◽  
The Other ◽  
Poverty Traps ◽  
Poverty Trap ◽  
Multiple Steady States ◽  
The World ◽  
State Capital

We extend the dynamic Heckscher–Ohlin model in Bond et al. [Economic Theory(48, 171–204, 2011)] and show that if the labor-intensive good is inferior, then there may exist multiple steady states in autarky and poverty traps can arise. Poverty traps for the world economy, in the form of Pareto-dominated steady states, are also shown to exist. We show that the opening of trade can have the effect of pulling the initially poorer country out of a poverty trap, with both countries having steady state capital stocks exceeding the autarky level. However, trade can also pull an initially richer country into a poverty trap. These possibilities are a sharp contrast with dynamic Heckscher–Ohlin models with normality in consumption, where the country with the larger (smaller) capital stock than the other will reach a steady state where the level of welfare is higher (lower) than in the autarkic steady state.

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