The Journal of Membrane Biology

Krasne, S.; Eisenman, G.

doi: 10.1007/BF01869658pmid: 1037004

The manner in which the molecular structure of the carrier and the lipid composition of the membrane modulate the membrane selectivity among monovalent cations has been investigated for nonactin, trinactin, and tetranactin, which differ only in their degrees of methylation, and for membranes made of two lipids, phosphatidyl ethanolamine and glyceryl dioleate, in which “equilibrium” and “kinetic” aspects of permeation, respectively, are emphasized. Bilayer permeability ratios for Li, Na, K, Rb, Cs, Tl, and NH4 have been characterized and resolved into “equilibrium” and “kinetic” components using a model for carrier-mediated membrane transport which includes both a trapezoidal energy barrier for translocation of the complex across the membrane interior and a potential-dependence of the loading and unloading of ions at the membrane-solution interfaces. The bilayer permeability properties due to tetranactin have been characterized in each of these lipids and found not only to be regular but to be systematically related to those of the less methylated homologues, trinactin and nonactin. This analysis has led to the following conclusions: (1) The change in lipid composition alters the relative contributions of “kinetic”vs. “equilibrium” components to the observed carrier-mediated selectivity. (2) Increased methylation of the carrier increases the contribution of the “kinetic” component to the selectivity relative to that of the “equilibrium” component and additionally alters the “equilibrium” component sufficiently that an inversion in Cs−Na selectivity occurs between trinactin and tetranactin. (3) For all ions and carriers examined, the “reaction plane” for ion-carrier complexation and the width for the “diffusion barrier” can be represented by the same two parameters, independent of the ion or carrier, so that in all cases the complexation reaction senses 10% of the applied potential and the plateau of the “diffusion barrier” extends across 70% of the membrane interior.

Ciani, S.

doi: 10.1007/BF01869659pmid: 1011245

The steady-state electrical properties induced by neutral carriers of ions in lipid bilayer membranes and the time dependence of the membrane current for low applied voltages are described theoretically in terms of a model which allows for a voltage dependence of the interfacial reactions, as well as for a trapezoidal shape of the internal free energy barrier for translocation of the complex. The basic features of the model are closely related to those of others presented previously (J.E. Hall, C.A. Mead & G. Szabo, 1973,J. Membrane Biol. 11:75; S.B. Hladky, 1974,Biochim. Biophys. Acta 352:71; S.B. Hladky, 1975,Biochim. Biophys. Acta 375:327; Eisenman, Krasne & Ciani, 1975,Ann. N.Y. Acad. Sci. 264:34), but the analysis of its consequences on the steady-state and nonsteady-state electrical characteristics is given here in greater detail and is extended to provide the expression for the zero-current potential in ionic gradients. It is shown that parameters, such as the width of the trapezoidal barrier, the plane of the reaction and the ratio of the rate constant of translocation across the membrane interior to the rate constant of dissociation of the complex, can be deduced from steady-state analysis, whereas the individual values of these constants and the distance between the equilibrium positions of the complexes are deducible from relaxation measurements.

Canessa, Mitzy; Labarca, Pedro; Leaf, Alexander

doi: 10.1007/BF01869660pmid: 827615

The possibility that sodium from the serosal bathing medium “back-diffuses” into the active sodium transport pool within the mucosal epithelial cell of the isolated toad bladder was examined by determining the effect on the metabolism of the tissue of removing sodium from the serosal medium. It was expected that if recycling of serosal sodium did occur through the active transepithelial transport pathway of the isolated toad bladder, removal of sodium from the serosal medium would reduce the rate of CO2 production by the tissue and enhance the stoichiometric ratio of sodium ions transported across the bladder per molecule of sodium transport dependent CO2 produced simultaneously by the bladder (J Na/J CO 2). The data revealed no significant change in this ratio (17.19 with serosal sodium and 16.13 after replacing serosal sodium with choline). Further, when transepithelial sodium transport was inhibited (a) by adding amiloride to the mucosal medium, or (b) by removing sodium from the mucosal medium, subsequent removal of sodium from the serosal medium, or (c) addition of ouabain failed to depress the basal rate of CO2 production by the bladder [(a) rate of basal, nontransport related, CO2 production (J CO2 b ) equals 1.54±0.52 with serosal sodium and 1.54±0.37 without serosal sodium; (b)J CO2 b equals 2.18±0.21 with serosal sodium and 2.09±0.21 without serosal sodium; (c) 1.14±0.26 without ouabain and 1.13±0.25 with ouabain; unite ofJ CO2 b are nmoles mg d.w.−1 min−1]. The results support the hypothesis that little, if any, recycling of serosal sodium occurs in the toad bladder.

Meissner, Gerhard; McKinley, Dana

doi: 10.1007/BF01869661pmid: 1011246

Permeability properties and the effects of a changed membrane potential on Ca2+ release of sarcoplasmic reticulum vesicles of rabbit skeletal muscle were investigated by Millipore filtration. The relative permeability of sarcoplasmic reticulum to solutes determined under conditions of isotope exchange at equilibrium and/or under conditions of net flow of solute and water into the vesicles was as follows: sucrose, Ca2+, Mn2+<gluconate−, choline+, Tris+<methanesulfonate−<urea, glycerol, K+, Na+, Li+, Cl−. Transient membrane potentials were induced by rapidly changing the ionic environment of the vesicles. Knowledge of the relative permeation rates of the above ions allowed prediction of the direction and extent of membrane polarization. Osmotic effects in the polarization measurements due to the rapid influx of solute and water into the vesicles were minimized by using media containing a fast (K+ or Cl−) and a relatively slow (gluconate− or choline+) penetrating ion.45Ca2+ efflux from vesicles derived from different parts of the sarcoplasmic reticulum structure was not appreciably changed when vesicles were made more positive inside (choline chloride → potassium gluconate) or more negative inside (potassium gluconate → choline chloride). These studies suggest that part or all of the ion-induced changes in sarcoplasmic reticulum membrane permeability, previously interpreted to indicate “depolarization”-induced Ca2+ release, may be due to osmotic effects.

Schein, Stanley; Colombini, Marco; Finkelstein, Alan

doi: 10.1007/BF01869662pmid: 1011248

We have incorporated into planar lipid bilayer membranes a voltage-dependent, anion-selective channel (VDAC) obtained fromParamecium aurelia. VDAC-containing membranes have the following properties: (1) The steady-state conductance of a many-channel membrane is maximal when the transmembrane potential is zero and decreases as a steep function of both positive and negative voltage. (2) The fraction of time that an individual channel stays open is strongly voltage dependent in a manner that parallels the voltage dependence of a many-channel membrane. (3) The conductance of the open channel is about 500 pmho in 0.1 to 1.0m salt solutions and is ohmic. (4) The channel is about 7 times more permeable to Cl− than to K+ and is impermeable to Ca++. The procedure for obtaining VDAC and the properties of the channel are highly reproducible.

Sone, Nobuhito; Yoshida, Masasuke; Hirata, Hajime; Okamoto, Harumasa; Kagawa, Yasuo

doi: 10.1007/BF01869663pmid: 13221

Measurements were made of the difference in the electrochemical potential of protons ( $$\Delta \bar \mu H^ + $$ ) across the membrane of vesicles reconstituted from the ATPase complex (TF 0 ·F 1) purified from a thermophilic bacterium and P-lipids. Two fluorescent dyes, anilinonaphthalene sulfonate (ANS) and 9-aminoacridine (9AA) were used as probes for measuring the membrane potential (ΔΨ) and pH difference across the membrane (Δ pH), respectively.

Zimmermann, U.; Pilwat, G.; Holzapfel, Chr; Rosenheck, K.

doi: 10.1007/BF01869664pmid: 13222

The external electric field strength required for electrical hemolysis of human red blood cells depends sensitively on the composition of the external medium. In isotonic NaCl und KCl solutions the onset of electrical hemolysis is observed at 4 kV per cm and 50% hemolysis at 6 kV per cm, whereas increasing concentrations of phosphate, sulphate, sucrose, inulin and EDTA shift the onset and the 50% hemolysis-value to higher field strengths. The most pronounced effect is observed for inulin and EDTA. In the presence of these substances the threshold value of the electric field strength is shifted to 14 kV per cm. This is in contrast to the dielectric breakdown voltage of human red blood cells which is unaltered by these substances and was measured to be ∼1 V corresponding in the electrolytical discharge chamber to an external electric field strength of 2 to 3 kV per cm. On the other hand, dielectric breakdown of bovine red blood cell membranes occurs in NaCl solution at 4 to 5 kV per cm and is coupled directly with hemoglobin release. The electrical hemolysis of cells of this species is unaffected by the above substances with exception of inulin. Inulin suppressed the electrical hemolysis up to 15 kV per cm. The data can be explained by the assumption that the reflection coefficients of the membranes of these two species to bivalent anions and uncharged molecules are field-dependent to a different extent. This explanation implies that electrical hemolysis is a secondary process of osmotic nature induced by the reversible permeability change of the membrane (dielectric breakdown) in response to an electric field. This view is supported by the observation that the mean volumes of ghost cells obtained by electrical hemolysis can be changed by changing the external phosphate concentration during hemolysis and resealing, or by subjecting the cells to a transient osmotic stress immediately after the electrical hemolysis step. An interesting finding is that the breakdown voltage, although constant throughout each normally distributed ghost size distribution, increases with increasing mean volume of the ghost populations.

Blaustein, M.; King, A.

doi: 10.1007/BF01869665pmid: 1011247

Sodium, potassium and veratridine were tested for their effects on the uptake of gamma-aminobutyric acid (GABA) by pinched-off presynaptic nerve terminals (synaptosomes). As noted by previous investigators, the uptake from media containing 1 μm GABA (“high-affinity” uptake) is markedly Na-dependent; the uptake averaged 65 pmoles/mg synaptosome protein × min, with [Na]0=145mm and [K]0=5mm, and declined by about 90% when the external Na concentration ([Na]0) was reduced to 13mm (Na replaced by Li). The relationship between [Na]0 and GABA uptake was sigmoid, suggesting that two or more Na+ ions may be required to activate the uptake of one GABA molecule. Thermodynamic considerations indicate that with a Na+/GABA stoichiometry of 2∶1, the Na electrochemical gradient, alone, could provide sufficient energy to maintain a maximum steady-state GABA gradient ([GABA] i /[GABA]0) of about 104 across the plasma membrane of GABA-nergic terminals.

Azarnia, R.; Loewenstein, W.

doi: 10.1007/BF01869666pmid: 189035

A cancer (hepatoma) cell strain is described in which the formation of junctional membrane channels is abnormally slow. The development of electrical junctional coupling following the establishment of contact between these (reaggregated) cells is at least 15 times slower than that between their normal counterparts; and junctional transfer of fluorescein eventually develops, but only in about 5% of the contacts (as against 100% normally). This deviant membrane behavior is interpreted as a retardation in the process of accretion of junctional membrane channels. Its possible etiological role in defective growth regulation is discussed.

Frazier, Loy

doi: 10.1007/BF01869667pmid: 13223

The urinary bladder ofBufo marinus excretes H+ and NH 4 + , and the H+ excretion is increased after the animal is placed in metabolic acidosis. The present study was done to determine if parathyroid hormone could stimulate the bladder to increase the excretion of H+ and/or NH 4 + . Parathyroid hormone added to the serosal solution in a final concentration of 10 μg/ml was found to increase H+ excretion by 50% above the control hemibladders, while there was no effect on NH 4 + excretion. Parathyroid hormone had no effect on H+ excretion when added to the mucosal solution. We also performed experiments utilizing theophylline and dibutyryl cyclic AMP which mimicked those of the parathyroid hormone experiments. A dose-response analysis was performed and the results indicate that 1 μg/ml of parathyroid hormone was the minimal effective dose. These results suggest that parathyroid hormone can stimulate H+ excretion in the toad urinary bladder and this effect seems to be mediated by cyclic AMP. In addition, it was found that parathyroid hormone has no effect on NH 4 + excretion.