Akihiko Irimajiri

A dielectric theory of “multi-stratified shell” model with its application to a lymphoma cell

Abstract A theory of complex dielectric constant ( e ∗ ) for the suspension of “multi-stratified” spherical particles is presented. Based on Maxwells theory of interfacial polarization, we derive a general expression which correlates e ∗ with the electrical and geometrical parameters of each stratum. It can be shown that such a “multi-stratified” system in general should give rise to multiple dielectric dispersions, the number of which corresponds to the number of interfaces lying between the successive shell phases. The conditions for a full number of different “unit” dispersions to occur are also discussed. As an example, a special case of the “double-shell” model consisting of a spherical core and three layers of concentric phases is solved numerically by using a set of parameter values pertinent to a lymphoma cell. In light of the characteristic behavior of e ∗ thus revealed, we propose a scheme of procedure that applies to the determination of electrical parameters associated with the specific “double-shell” model.

Electrical properties and active solute transport in rat small intestine

SummaryAddition ofd-glucose to the mucosal fluid resulted in a significant depolarization of the mucosal membrane potential (Vm) in rat duodenum, jejunum, and ileum accompanied by an increase in the transepithelial potential difference (PDt). On the other hand,l-glucose did not inducePDt andVm changes. Glycine applied from the mucosal side also inducedVm-depolarization andPDt-increment in the ileum. Phlorizin added to the mucosal fluid or ouabain added to the serosal fluid inhibited the sugar-dependent changes inPDt andVm.According to the analysis with an equivalent circuit model for the epithelium, it was concluded that an actively transported solute induced not only a depolarization of the mucosal (brush border) membrane but also a hyperpolarization of the serosal (baso-lateral) membrane of an epithelial cell, so that the origin of solute-inducedPDt changes should be attributed to changes in emfs at both membranes. The hyperpolarization of the serosal membrane in the presence of an actively transported solute was attributed to a mechanism of serosal electrogenic sodium pump stimulated by the increase in the extrusion rate of Na+ co-transported into the cell with sugar or amino acid.

Passive electrical properties of cultured murine lymphoblast (L5178Y) with reference to its cytoplasmic membrane, nuclear envelope, and intracellular phases

SummaryDielectric dispersion measurements over a frequency range 0.01–100 MHz were made with the suspensions of a cultured cell line, mouse lymphoma L5178Y, and an attempt to explain the observed dielectric behavior by taking explicitly into consideration the possible involvement of cell nucleus has been presented.The use of a conventional “single-shell” model in which the cell is represented by a homogeneous sphere coated with a thin limiting shell phase did not duplicate the observed dispersion curves, whereas a “double-shell” model in which one additional concentric shell is incorporated into the “single-shell” model gave a much better fit between the observed and the predicted dispersion curves. Based on the latter model, we analyzed the raw data of dielectric measurements to yield a set of plausible electrical parameters for the lymphoma cell:CM≅1.0μF/cm2,CN≅0.4μF/cm2, εk≅300, κc/κa≅0.9, and κk/κc≅0.7. Here,CM andCN are the specific capacities of plasma and nuclear membranes; ε and κ are the dielectric constant and conductivity with subscripta, c andk referring respectively to the extracellular, the cytoplasmic and the karyoplasmic phases.

Electrical properties and active solute transport in rat small intestine. II. Conductive properties of transepithelial routes.

SummaryThe transepithelial resistance, the cell membrane resistance and the ratio of resistances of the serosal (baso-lateral) to the mucosal (brush border) cell membrane were measured in rat duodenum, jejunum and ileum by means of microelectrode techniques. These measured values were not affected in the presence of actively transported solutes in the mucosal bathing fluid.Contribution of an electrical conductance through the extracellular shunt pathway to the total transepithelial conductance was quantitatively estimated using an electrically equivalent circuit analysis. These values estimated in respective tissues of small intestine were approx. 95% of the total transepithelial conductance, remaining unaffected by an active solute transport.From these data, the changes in emfs of the mucosal and serosal membrane induced byd-glucose or glycine were separately evaluated.

A method for determining the dielectric constant and the conductivity of membrane-bounded particles of biological relevance

Numerical assessment is made regarding Pauly and Schwans theory which describes the dielectric behaviour of a suspension of “shell spheres” as a model of biological membrane-bounded particles. The results indicate that approximate expressions of the theory may give rise to serious errors when applied to particles smaller than about 1 Μm in diameter. With a view to performing analysis according to a general expression of the theory, some of the characteristic responses of dielectric parameters upon changes in phase parameters are examined with particular reference to some numerical ranges of biological interest. On this basis a simplified and systematic procedure is proposed for estimating the phase parameters of particles whose shell phase can be regarded as non-conductive. As the application of the procedure proposed, a set of dielectric data of a synaptosome suspension is analyzed, so that the following three phase parameters are successfully determined: membrane capacitance (or shell phase dielectric constant), internal phase conductivity and internal phase dielectric constant. Some limitations of the procedure are discussed for the cases of conducting shells and small particles.

Evaluation of a conductometric method to determine the volume fraction of the suspensions of biomembrane-bounded particles.

Supported by the fact of correspondence between the results of several independent techniques compared, we recommend here a conductometric method as a simple, nondestructive and reliable tool for determining the volume fraction of the suspensions of membrane-limited particles of biological relevance. It requires only conductivity measurements on a suspension and its medium.

Dielectric dispersion of a single spherical bilayer membrane in suspension

Abstract Single spherical bilayer membranes of the Pagano-Thompson type (Pagano, R. and Thompson, T.E. (1967) Biochim. Biophys. Acta 144, 666–669), formed from monooleyl phosphate and cholesterol dissolved in CHCl 3 /CH 3 OH/ n -decane, were subjected to a fast impedance analysis of high precision. Dielectric behavior of the whole system, as monitored from outside the spherical membrane, was sensitive to changes in the membrane state from the thick colored to the thin black state. With a spherical membrane 2–3 mm in diameter formed in the sample cavity containing 0.12 ml 10 mM NaCl, the former state was characterized by a dielectric dispersion having dielectric increment (Δϵ) of some 10 2 and characteristic frequency ( ƒ c ) around 10 6 Hz, while the latter had Δϵ ≅ 10 5 and ƒ c ≅ 10 3 Hz . Complex plane plots for both dispersions traced semicircles, indicating that the present system may be unequivocally analyzed to yield spherical radius and membrane capacity ( C m ) on the basis of a well-established dielectric theory. C m for the thin membranes has thus been determined to be 0.54 μF · cm −2 , in excellent agreement with a separate determination on planar membranes. The applicability of the present type of spherical membranes under dielectric monitoring to the study of membrane fusion or of exocytosis is suggested.

TRANSIENT KINETICS FOR Ca UPTAKE BY FRAGMENTED SARCOPLASMIC RETICULUM FROM BULLFROG SKELETAL MUSCLE WITH REFERENCE TO THE RATE OF RELAXATION OF LIVING MUSCLE

The transient kinetics of Ca uptake for fragmented sarcoplasmic reticulum from bullfrog skeletal muscle was determined spectrophotometrically in the presence of tetramethylmurexide as a Ca indicator by a stopped-flow method in view of understanding the time course of muscle relaxation in terms of the transient Ca uptake rate. The initial uptake rate depended on the concentration of MgATP, the pH of the medium, and the concentration of Mg 2+ . Under the optimum conditions for the initial uptake rate, i.e. pH 6.80, 1 mM Mg 2+ and 0.5 mM MgATP, the transient time course of Ca uptake was composed of two components of first-order kinetics: the rapid component of an apparent rate constant of 40–60 s −1 and the slow component of an apparent rate constant of 2–3 s −1 at 15°C in the presence of 0.35 mg protein/ml. High concentrations of MgATP, 0.5 mM or more, are required for the observation of the rapid component. Both apparent rate constants appear to be proportional to the amount of FSR in the medium. The ratio of the amplitude for the rapid component to that for the slow one was estimated to be 1:5–10. The temperature coefficient, Q 10 , for the initial uptake rate was 3.0, which corresponded to that for the relaxation rate of living muscle. The time course of muscle relaxation was discussed in reference with these observations, taking account of sarcoplasmic reticulum content (9mg protein/g muscle wet weight), and myoplasmic Ca 2+ concentration.

Dielectric properties of synaptosomes isolated from rat brain cortex

Dielectric measurements were performed on the suspensions of synaptosomes isolated from rat brain cortex. The synaptosomes in buffered salt media showed typical dielectric dispersions caused by the presence of a thin limiting membrane of sufficiently low conductivity. An analysis of the dielectric data revealed that the electric conductivity of the synaptosome interior was about 37 % of the external medium conductivity under isotonic conditions and that the dielectric constant for the interior phase was about 35. The membrane capacitance (0.7 ΜF cm−2) remained constant irrespective of nature and concentration of the univalent salts examined. Significant reduction in both the conductivity and the dielectric constant of the internal phase can be explained theoretically provided that some intra-synaptosomal structure (synaptic vesicles and/or small mitochondria) of non-conducting nature occupies about 50 % of the particulate volume, the remainder being in equilibrium with the external salt medium.

Permeability properties and intracellular ion concentrations of epithelial cells in rat duodenum

Effects of the K+ concentration in the bathing fluid ([K+]l) on the intracellular K+, Na+ and Cl- concentrations ([K+]i [Na+]i and [Cl-]i) as well as on the electrical potential were studied in rat duodenum. Changes in the mucosal K+ concentration ([K+]m), bringing the sum of Na+ and K+ concentrations to 147.2 mM constant, had little effect on the transmural potential difference (PDt), but did induce marked changes in the mucosal membrane potential (Vm). As [K+]m increased, Vm was depolarized gradually and obeyed the Nernst equation for a potassium electrode in the range of [K+]m greater than approx. 60 mM. Experiments of ion analyses were carried out on strips of duodenum to determine the effect of changing the external K+ concentrations on [K+] i, [Na+]i and [Cl-]i. An increase in [K+]o resulted in increases in [K+]i and [Cl-]i and a decrease in [Na+]i, [K+]i approaching its maximum at [K+]o greater than 70 mM. Such changes in [K+]i and [Na+]i seem to correlate quantitatively with the changes in [K+]o and [Na+]o. The values of the ratio of permeability coefficients, Pna+/PK+ were estimated using the Vm values and intracellular ion concentrations measured in these experiments. The results suggested that there appeared a rather abrupt increase in the PNa+/PK+ ratio from 0 to approx. 0.1, as [K+]m decreased.