Kozue Kaibara

Nonequilibrium thermodynamics of ion transport through membranes

Abstract A theory of membrane ion transport suitable for a self-consistent analysis of transport phenomena is presented on the basis of nonequilibrium thermodynamics. The theory assumes only a steady state and no volume flow across the membrane. Ion flow is expressed as a linear function of the total ion activity difference across the membrane. Coefficients of the flux equation are defined as elements of a permeability matrix. The equations for the membrane properties (e.g., potential and conductance) are derived from the equation of ion flux. The theory is applicable to any multi-ionic system containing ions of various charges. A physical representation of membrane permeability and a correlation between membrane permeability and the elements of a permeability matrix are explained. Transport phenomena are discussed with respect to the theory presented.

Characterizations of critical processes in liquid–liquid phase separation of the elastomeric protein–water system: Microscopic observations and light scattering measurements

Biological self‐assembly process of tropoelastin in an extracellular space, viewed as a key step of the elastogenesis, can be mimicked by the temperature‐dependent coacervation of the elastin‐related polypeptide–water system. Early and late stages of the phase separation behavior of the bovine neck ligamental α‐elastin–water system were examined respectively by the laser light scattering photometry and phase contrast microscopy. Changes in the hydrodynamic size of molecular assemblies and visible microcoacervate droplet size were traced as a function of the concentration of α‐elastin and temperature. Near the critical point, α‐elastin concentration of 0.11 mg/mL and temperature of 21.5°C, the phase separation was initiated after fast increase of the hydrodynamic size of primary aggregates as scattering particles and followed by the appearance of larger microcoacervate droplets with a broad size distribution. Whereas in the off‐critical region, slow decrease of the hydrodynamic size of primary particles induced phase separation with smaller droplets of a narrow size distribution. Observation of the phase separation processes in the α‐elastin–water system with metal chlorides and hydrophobic synthetic model polypeptide–water system indicated that the fast and slow molecular assembly processes were based on the fundamental hydrophobic interactions and involvements of electrostatic interactions between charged amino acid residues, respectively.

Study of ion transport across an amphoteric ion exchange membrane — general transport properties of a simple electrolyte

Abstract Basic electrochemical properties of an amphoteric ion-exchange membrane (1.0—PA—29), in which almost equal numbers of cationic and anionic sites are distributed homogeneously over the functionalized polymer networks, were studied for a variety of concentration-cell systems. Unlike the usual uniform ion-exchange membrane, potentiometric permselectivities were demonstrated even for ions of the same charge, as shown by the result that distinctive potential responses were observed for a series of alkali metal chloride, sodium salt, and tetra-alkylammonium chloride systems. The sequence of membrane permeabilities to cations and anions calculated from the electrochemical data could well be correlated to the sequence of the hydrated radii of the respective ions. So the potentiometric responses to any electrolyte system can be predicted from the permeability data or hydrated radius values of individual cations and anions. The present results suggest that the homogeneous amphoteric ion-exchange membrane functions effectively as an ion sieve, sifting out the sizes of permeating hydrated cations and anions.

β-Adrenergic modulation of the Na+−K+ pump in frog skeletal muscles

AbstractAdrenaline markedly increased the ouabain-sensitive22Na+-efflux by stimulating the Na+−K+ pump in frog skeletal muscle. The facilitatory effects of adrenaline had the following properties.1.The effects of adrenaline on the ouabain-sensitive Na+-efflux were observed at concentrations greater than 0.1 μM and the magnitude increased with concentration up to 10 μM.2.At a concentration of 30 μM, adrenaline markedly augmented the ouabain-sensitive Na+-efflux, but other biogenic amines were less effective (noradrenaline and dopamine) or ineffective (histamine and serotonin).3.The increase of Na+-efflux induced by 1 μM adrenaline was blocked by 3 μM propranolol, but not by 3 μM phenoxybenzamine. The properties of the facilitatory action of adrenaline on the ouabain-sensitive Na+-efflux suggest that β-adrenoceptors have an important role in modulating the Na+−K+ pump activity in the skeletal muscle membrane. The protein complex localized in excitable membranes, namely the Na+−K+ ATPase-β-adrenoceptor complex, may be the functional unit which operates the membrane machinery driving the Na+−K+ pump.

Characteristic interaction of Ca2+ ions with elastin coacervate: Ion transport study across coacervate layers of α‐elastin and elastin model polypeptide, (Val‐Pro‐Gly‐Val‐Gly)n

Ion transport characteristics across a macrocoacervate layer membrane composed of aqueous elastin model polypeptides with a specific repeating pentapeptide sequence, H-(Val-Pro-Gly-Val-Gly)n-Val-OMe (n > or = 40), were investigated. Transmembrane potential responses for NaCl. MgCl2, and CaCl2 concentration-cell systems were measured and examined systematically by comparing with those across a coacervate membrane composed of bovine neck ligamental alpha-elastin. In the case of the NaCl and MgCl2 systems, potential responses across these protein liquid membranes were different noticeably from each other depending upon the molecular structure with and without charged peptide side chains, whereas in the CaCl2 systems the transmembrane potential responses across the noncharged polypentapeptide coacervate membrane were comparable with those across the alpha-elastin coacervate membrane carrying both the positively and negatively charged amino acid residues as an amphoteric ion-exchange membrane. These results indicated that mechanisms of major Ca2+ ion transport are based on the specific and selective interactions with electrically neutral sites of elastin, such as the polypentapeptide backbone chain.

Effects of anion exchange resin as phosphate binder on serum phosphate and iPTH levels in normal rats

In order to investigate the characteristics of anion exchange resins that may safely and effectively bind dietary phosphate in digestive tract, phosphate binding experiments were carried out in vitro and in vivo with normal rats by comparing anion exchange resins, PAA-B (which has the same chemical structure as Sevelamer® HCl) and Dowe 1x8, with CaCO3. In in vitro phosphate binding experiments, PAA-B bound 32.3% less phosphate than CaCO3 at pH 7. In the rat dietary phosphorus excretion experiments, PAA-B, Dowex 1x8, and CaCO3 increased fecal phosphorus excretion by 62.7, 32.3, and 84.0%, respectively. Famotidine significantly reduced the phosphate binding of CaCO3. When phosphate solution was orally adiministered, PAA-B depressed serum phosphorus augmentations immediately after administration and thereafter effectively depressed serum iPTH. This suggests that anion exchange resins with most primary and secondary amino type anion exchange groups, have bright prospects in the treatment of hyperphosphatemia. (Int J Artif Organs 2000; 23: 243–9)

Dynamic Light Scattering Study of Coacervation of α-Elastin

The coacervation process of elastomeric protein α-elastin in aqueous solutions was investigated as a function of temperature by using dynamic light scattering. Two kinds of dynamical behaviors were found, which were dependent on both the concentration and the scattering vector. Near the critical point, the diffusion coefficient, deduced from the relaxation time, showed a remarkable decrease. When far from the critical concentration, on the contrary, the diffusion coefficient showed a gradual increase on raising the temperature, followed by a rapid increase near the temperature at which the sample started to be turbid. The results agree with recent findings on the role of the critical fluctuations on the condensation of biostructural polymers leading to the supramolecular ordering.

Observation of Critical Behaviors in an Elastomeric Protein-Water System

The intensity of the scattered light and the turbidity of aqueous solutions of the protein of the elastic fiber, α-elastin have been measured as a function of temperature and concentration. The coexistence curve and the spinodal curve were determined from the turbidity and the angular dependence of the scattered intensity, respectively. These two curves had minima which coincided near the concentration of 0.11 mg/ml and the temperature of 21.5°C. At this point, critical divergences of the forward scattering light intensity and the correlation length were observed.

A kinetic analysis of the facilitatory action of adrenaline.

The22Na+-efflux from skeletal muscle cells of frog (Rananigromaculata) was measured in Ringer solutions containing different concentrations of K+ (0.1 to 30 mM). The effects of adrenaline (30 μM) and ouabain (10 μM) on the22Na+-efflux were investigated for the purpose to clarify the mechanism of the facilitatory effect of adrenaline on Na+−K+ pump. The rate coefficient for the ouabain-sensitive22Na+-efflux increases with increasing extracellular K+ concentrations and adrenaline potently facilitates these rate coefficients. On the basis of Michaelis-Menten type kinetics assumed for the reaction between pump site and extracellular K+, it is concluded that adrenaline decreases the dissociation constant (Km), and increases the maximum Na+-efflux.

Ion transport mediated by inverted micellar aggregates across a phosphatidylcholine-octanol liquid membrane

Abstract The ionophoretic activity of dipalmitoyl-DL-α-phosphatidylcholine (DPPC) was investigated on the system in which two aqueous NaCl solutions are separated by a porous support membrane impregnated with a 1-octanol solution of DPPC. Transmembrane potential and conductance measurements were carried out with changing temperature to estimate the membrane permeability to ions. To clarify the mechanism of ion transport through an immobilized DPPC-1-ctanol membrane, differential scanning calorimetry and photon correlation spectroscopy were employed to investigate the molecular properties of DPPC in a water-saturated 1-octanol system. An endothermic peak was detected at around 18°C in the water-saturated 1-octanol system, but not in the pure 1-ctanol system. Laser light scattering study indicated that DPPC molecules form aggregates, ca. 0.1 μm in diameter, in water-saturated 1-octanol, but not in pure 1-octanol. Temperature dependences of the relaxation time estimated by the light scattering study changed above and below 18°C. The critical temperature, 18°C, correlates well with that at which modes of the temperature dependences of membrane permeability are altered. Results obtained by these three types of experiments indicate that inverted micellar aggregates of DPPC function as an ionophore.