Comparison of jumping and electrodiffusion mechanisms of particle movement in thin membranes. II. Potential clamping. Jumping and continuous uniform mechanism]

Electric relaxation of the membrane in three-barrier hopping and electrodiffusion uniform models has been considered. Both models are shown to have different relaxation characteristics which do not coiside with each other.     

An irreversible thermodynamics treatment of electrodiffusion in uniform membranes

Summary In a previous paper (Ciani andGliozzi, 1966) we presented the integration of the phenomenological equations of flow of irreversible thermodynamics, describing the movement of water and two monovalent counterions across a uniform permselective membrane. The present paper generalizes those results, by introducing less restrictive assumptions and by allowing for the case that two counterions of different valences or one counterion and one coion are present in the membrane.The analytical expressions for the voltage-current relationship, the fluxes of the mobile species and the profiles of the concentrations are derived. The membrane resistance and the rectification properties of the system are analyzed in detail.The expression of the flux of water is found to allow for negative electroosmosis.Some comparative remarks between the present treatment and the earlier theory bySchlögl andSchödel (Schlögl andSchödel, 1955) are presented in the last section of the paper.     

Comparison of discrete models of charge transfer in thin membranes. I. Stationary regime]

The model of the ion transport through thin membranes is discussed. It is assumed that there exist some steps of the ion transfer in the membrane volume. Theory of absolute rate of processes is used to derive an equation for stationary transmembrane flow. As a result the thory parameters are connected with the form of potential energy curve of permeable ions into the membrane phase.     

Effect of ionic polarizability on electrodiffusion in lipid bilayer membranes.

Ion-carrier complexes and organic ions of similar size and shape have mobilities in lipid bilayer membranes which span several orders of magnitude. In this communication, an examination is made of the hypothesis that the basis for this unusually wide range of ionic mobilities is the potential energy barrier arising from image forces which selectively act on ions according to their polarizability. Using Poisson's equation to evaluate the electrostatic interaction between an ion and its surroundings, the potential energy barrier to ion transport due to image effects is computed, with the result that the potential energy barrier height depends strongly on ionic polarizability. Theoretical membrane potential energy profile calculations are used in conjunction with Nernst-Planck electrodiffusion equation to analyze the available mobility data for several ion-carrier complexes and lipid-soluble ions in lipid bilayer membranes. The variation among the mobilities of different ions is shown to be in agreement with theoretical predictions based on ionic polarizability and size. Furthermore, the important influence exerted by image forces on ion transport in lipid bilayer membranes compared to the frictional effect of membrane viscosity is established by contrasting available data on the activation energy of ionic conductivity with that for membrane fluidity.     

Semiconductor theory of ion transport in thin lipid membranes: I. Potential and field distributions

In the theory as presented in this paper and the following one, we shall attempt to apply the semiconductor principles and methods to the study of ion transport in thin lipid membranes. Detailed formulations are given on the potential energy barriers at the interfaces, voltage drops in the polar and non-polar regions, and potential and field distributions in the diffuse double layer and within a charged membrane. These results will be used mainly as the boundary conditions for the solution of ion flow as to be given in the following paper. The analysis clearly indicates that the ion transport is interface-limited and is profoundly influenced by the presence of surface charges. An explanation of Na⁺ extrusion in nerve membrane is given based on the field distribution analysis. The theory also suggests that the “membrane potential” depends mainly on surface charges but not necessarily on ion permeation through the membrane.     

Simulations of voltage clamping poorly space-clamped voltage-dependent conductances in a uniform cylindrical neurite

Significant error is made by using a point voltage clamp to measure active ionic current properties in poorly space-clamped cells. This can even occur when there are no obvious signs of poor spatial control. We evaluated this error for experiments that employ an isochronal I(V) approach to analyzing clamp currents. Simulated voltage clamp experiments were run on a model neuron having a uniform distribution of a single voltage-gated inactivating ionic current channel along an elongate, but electrotonically compact, process. Isochronal Boltzmann I(V) and kinetic parameter values obtained by fitting the Hodgkin-Huxley equations to the clamp currents were compared with the values originally set in the model. Good fits were obtained for both inward and outward currents for moderate channel densities. Most parameter errors increased with conductance density. The activation rate parameters were more sensitive to poor space clamp than the I(V) parameters. Large errors can occur despite normal-looking clamp curves.     

Interaction between fascicles and tendinous structures during counter movement jumping investigated in vivo.

Behavior of fascicles and tendinous structures of the m. gastrocnemius medialis (MG) was quantitatively examined during human jumping in vivo. Eight male subjects performed maximal-effort counter movement jumping (CMJ) motions. Kinematic and kinetic data were obtained using a high-speed camera and a force platform. Behavior of fascicles and tendinous structures was determined using ultrasonography and electromyography. Although the muscle-tendon complex (MTC) shortened by only 1.6% during the downward phase of the counter movement, fascicles shortened as much as 10.4%. This shortening of fascicles caused elongation of tendinous structures by 2.2%. Although the MTC remained at almost constant length during the upward-I phase (-250 to -100 ms before toe-off), fascicles shortened by 19.2% of the initial length with an elongation of tendinous structures by 4.4%. The MTC shortened rapidly by 5.3% of the initial length during the upward-II phase (-100 to 0 ms), whereas fascicles shortened slightly during the first half of this phase and contracted in a quasi-isometric manner during the latter half of this phase. These findings implied that elastic energy was stored in tendinous structures throughout the latter half of the downward phase (1.0 J) and upward-I phase (5.6 J), which was thereafter rapidly released during the upward-II phase (3.8 J). It was found that muscle fibers of the MG were not stretched during counter movement; therefore, stretch reflex and potentiation of the contractile component of the MG might not contribute to the work enhancement in CMJ. It was suggested that the interaction between fascicles and tendinous structures was essential in a generation of higher joint power during the late push-off phase. This behavior of the MTC of the MG in CMJ was quite similar to what was observed in squat jumping performed without counter movement.     

Comparison of lectin receptor and membrane coat-associated glycoproteins of milk lipid globule membranes.

1. Glycoproteins of bovine (Bos taurus) and human (Homo sapiens) milk lipid globule membranes were characterized by ability to bind lectins after electrophoretic separation. 2. Seven lectin receptor glycoproteins were detected in bovine and five in human milk lipid globule membranes. Bovine and human globule membrane glycoproteins differed in ability to interact with certain lectins. 3. Two major nonionic detergent insoluble glycoproteins were present in bovine and human lipid globule membrane; these constituents had apparent molecular weights of 155,000 and 69,000. Detergent-insoluble polypeptides with similar or identical electrophoretic mobilities were found in milk lipid globule membranes from four other species, rat (Rattus norvegicus), sheep (Ovis aries), pig (Sus scrofa) and goat (Capra hircus). Tryptic peptide mapping revealed these polypeptides to be nonidentical among species.     

Properties of particle movement in the plasma membrane of 3T3 mouse fibroblasts

The effects of cytochalasin B, vinblastine and temperature on particle movement in the plasma membrane of several 3T3 mouse fibroblast lines were investigated. Preincubation of normal 3T3 cells for 24 h in 5–10 μg/ml cytochalasin B had no effect on the mean square relative displacement of marker particles in the membrane (motion constant), but preincubation for 4 h in 40 μg/ml vinblastine reduced the value of this constant by 70%. A 10 °C decrease in temperature decreased the motion constant in normal cells (Q₁₀ = 4) more than in virus-transformed 3T3 cells (Q₁₀ = 1.8). Interpreting the motion constant of the particles as an expression of the viscosity of the membrane material, values of 3 poise for normal 3T3 cells and 6 poise for the transformed cells are obtained for 37 °C and pH = 7.4.A method is suggested to quantitate aggregation of particles on the surface of cells. When this method is applied to gold particles on 3T3 cells, disaggregation of particles is seen to behave as an unordered process, whereas aggregation appears to express cellular control. This consideration and the effect of vinblastine indicate that the interpretation of particle movement as Brownian movement in a viscous membrane material does not cover all phenomena observed.The membrane movement of the flat revertant SVF1 101 [1] was investigated. This cell line occupies an intermediary position between normal 3T3 mouse fibroblasts and the polyoma and SV40 transformed 3T3 cell lines as judged by growth properties. Its membrane movement was found to occupy an intermediary position between the membrane movements of these cell lines, too.     

Rubella virus. III. Purification of infected or non-infected Vero cell membranes]

Separation of Vero cell membrane in a discontinuous sucrose gradient reveals five fractions. After infection a sixth fraction appears. It contains virioins but mostly modified membranes with subunits 5-6 nm in diameter, probably the hemagglutinin. None of the enzymes used was associated with this fraction. No modification of the other fractions was observed after infection.     

Lipolysis and lipid movement in a membrane model. Action of lipoprotein lipase.

The action of purified bovine milk lipoprotein lipase on tri[3H]oleoylglycerol and the effect of albumin on movement of lipolytic products at an argon-water interface were studied in a specially designed tricomparted trough. The amount of trioleoylglycerol applied was 14 times that needed to cover the surface of the aqueous subphase (0.1 M Tris . HCl, pH 7.4) with a monolayer. It is concluded that trioleoylglycerol was present in lenses on the surface of the aqueous subphase, that hydrolysis by lipoprotein lipase occurred in or near the lipid/argon-water interface, and that lipolytic products immediately located and spread throughout the interface, displacing substances with lower spreading pressures from the interface. Addition of albumin to the aqueous subphase accelerated markedly the desorption of oleic acid and monooleoylglycerol from the interface and thereby enhanced lipolysis. When albumin was not contiguous with the site of hydrolysis, oleic acid and monooleoylglycerol readily moved in the interface to the area of contact with albumin where they were desorbed from the interface. These findings support the hypothesis of transport of lipolytic products by lateral movement in cell membranes.     

Biochemical studies of the excitable membrane of Paramecium tetraurelia. III. Proteins of cilia and ciliary membranes

As a first step in the biochemical analysis of membrane excitation in wild-type Paramecium and its behavioral mutants we have defined the protein composition of the ciliary membrane of wild-type cells. The techniques for the isolation of cilia and ciliary membrane vesicles were refined. Membranes of high purity and integrity were obtained without the use of detergents. The fractions were characterized by electron microscopy, and the proteins of whole cilia, axonemes, and ciliary membrane vesicles were resolved by SDS polyacrylamide gel electrophoresis and isoelectric focusing in one and two dimensions. Protein patterns and EM appearance of the fractions were highly reproducible. Over 200 polypeptides were present in isolated cilia, most of which were recovered in the axonemal fraction. Trichocysts, which were sometimes present as a minor contaminant in ciliary preparations, were composed of a very distinct set of over 30 polypeptides of mol wt 11,000--19,000. Membrane vesicles contained up to 70 polypeptides of mol wt 15,000--250,000. The major vesicle species were a high molecular weight protein (the "immobilization antigen") and a group of acidic proteins with mol wt similar to or approximately 40,000. These and several other membrane proteins were specifically decreased or totally absent in the axoneme fraction. Tubulin, the major axonemal species, occurred only in trace amounts in isolated vesicles; the same was true for Tetrahymena ciliary membranes prepared by the methods described in this paper. A protein of mol wt 31,000, pI 6.8, was virtually absent in vesicles prepared from cells in exponential growth phase, but became prominent early in stationary phase in good correlation with cellular mating reactivity. This detailed characterization will provide the basis for comparison of the ciliary proteins of wild-type and behavioral mutants and for analysis of topography and function of membrane proteins. It will also be useful in future studies of trichocysts and mating reactions.     

Precipitation membranes: III. Reversible changes of membrane properties induced by alterations in ionic concentrations

Summary The conditioned state of a precipitation membrane with its particular properties exists within a limited range of membrane potentials and requires certain minimum concentrations,C _lim, of the generating ions in the adjoining solutions. We investigated these quantities for the BaSO₄ cellophane membrane and foundC _lim to be 10×10^–5 n (0.5×10^–4 m), equally for Ba⁺⁺ and SO ₄ ^–– . Beyond these limits, the membrane becomes deconditioned. This transformation is a reversible process provided the limits have not been surpassed too far. The capability for de- and reconditioning is a characteristic and unique property of precipitation membranes, not found in other membrane systems. The phenomenon is explained by the adsorption theory for precipitation membranes. It allows wide modifications and quick variations of the electrical properties and permeability of the membrane in an easy and reversible manner.     

The jumping mechanism of Xenopsylla cheopis. III. Execution of the jump and activity.

The flea's hind legs are the chief source of jumping power, but in species which execute large jumps, take-off is accelerated by elastic energy released from a resilin pad (homologous with the wing hinge ligaments of flying insects) situated in the pleural arch. A central click mechanism, operated by a rapid twitch of the trochanteral depressor (the starter muscle), synchronizes the separate sources of energy which power the jump. Ciné photos confirm the morphological evidence that the flea takes off from the trochanters, not the tarsi. The loss of wings, associated with lateral compression of the body and the shortening of the pleural ridge (which thus lowers the position of the pleural arch) together with modifications of the direct and indirect flight muscles, are some of the main morphological features associated with the change from a flying to a saltatorial mode of progression. The flea's take-off basically resembles that of other Panorpoid insects (Diptera, Mecoptera, etc.). The release of elastic energy from the pleural arch is a system by which the force used to move the wings of flying insects is rapidly fed back into the legs and adds power to the jump.     

Antigenic structure of the plasma membranes of mouse liver cells. III. Lipid haptens]

The total glycolipids, gangliosides, neutral lipids and some individual lipids of these fractions were isolated from the whole lipid extract of the mouse liver cell suspension. The antigenic activity of the isolated lipids was studied with the complement fixation test using the rabbit antisera against the liver cell ghosts. Active lipids were: glycosphingolipids, gangliosides, cardiolipin and fraction containing polar glyco- and phospholipid mixture. The cardiolipins isolated from animal cells of some species differed in their antigenic activity. With the immunofluorescence method, the absorbtion of antighost sera by lipid haptens resulted in a decreased fluorescence of plasma membranes of cells in the liver sections. This fact may evidence for the membrane localization of the studied haptens.