Molecular Dynamics and Experimental Study of the Effect of CeF3 and NdF3 Additives on the Physical Properties of FLiNaK.

The paper presents the results, which are consistent within 2%, obtained both in the simulation of molecular dynamics and in the experiment on the study of the kinetic properties of molten FLiNaK with addition of lanthanide fluorides. The parameters of the Born-Huggins-Meier potential for the interaction of CeF3 or NdF3 with FLiNaK components are first calculated using the ab initio approach. The enthalpy of the system with dissolved CeF3 or NdF3 calculated in the model increases by ∼4.4% over the entire temperature range studied (800 ≤ T ≤ 1020 K). The self-diffusion coefficients of the molten salt components are calculated from the Einstein relation and also estimated from the shear viscosity data. The temperature dependences of the shear viscosity of molten FLiNaK as well as FLiNaK with additions of 15 mol % CeF3 or NdF3 are determined experimentally and by calculation. In addition, the dependence of shear viscosity on the concentration of CeF3 and NdF3 in FLiNaK is measured and calculated. The linear growth of the shear viscosity with the CeF3 and NdF3 concentrations is obtained. Experimental dependence is in good agreement with the simulated results in the case of NdF3, and there is the discrepancy while CeF3 addition. An analytical approximation of the temperature and concentration dependences for the viscosity of molten FliNaK and for the calculated self-diffusion coefficients of constituent elements is proposed. Linear approximation of temperature dependence of the self-diffusion coefficients of similar components in the corresponding extended systems is presented.

HALOPERIDOL MODULATES IONIC TRANSPORT OF CHARA CORALLINA CELLS.

The effect of the haloperidol (HP), a dopamine D2-receptor antagonist on the function of ionic channels of the electrically excitable plasma membrane and on the cytoskeleton of Chara corallina cells was investigated. Haloperidol was shown to block plasmalemmal Ca2+ channels. Apart from Ca2+ current reduction, the presence of HP slowed the kinetics of both activation and inactivation of ionic channels. The influence of haloperidol on the membrane structure was reversible. After removal of the neuromodulator, both the amplitude and the kinetics of the current development were seen to be completely restored. HP had no effect on Ca2+-activated chloride channels. Haloperidol inhibited cytoplasmic motion related to microfilamentary complex. Once haloperidol was removed from cell washing solution, cytoplasmic motion was restored. These results let us to assume that in the presence of HP the concentration of free Ca2+ in cytoplasm increases. Also it can be assumed that plasmalemmal Ca2+-channels of Ch. corallina cells contain binding sites similar to dopamine receptors and their antagonists.

[Trabeculae and the intertrabelcular tissue during the contraction of the frog atrium at decreased temperatures and sodium ion concentrations in solution].

Data characterizing the kinetics of the contraction of trabeculae and the intertrabelcular tissue have been obtained. It has been concluded that trabeculae can act as conductors/transmitters of contraction across the myocardium and play a leading role in this process, while the functional role of the intertrabelcular tissue is secondary and more passive, and consists in the optimization and support of the contractile process.

[Slow Ca2'-binding Mg2+- EDTA buffer for intracellular perfusion].

In studies of currents in perfused cells or their membrane fragments containing potential-dependent Ca channels and Ca2+-activated channels, a buffer slowly binding Ca2+ appears useful in some cases. A buffer with EDTA in excess of Mg2+ has been proposed, and its kinetic characteristics have been calculated. It has been shown that this buffer, depending on its component proportions, may provide Ca2+ binding with a characteristic time of up to tens of milliseconds. For comparison, in the cytoplasm, this time does not exceed 1 ms even with a large calcium signal, as follows from calculations.

[Transient currents and Ca2+ gradient relaxation in characean algae cells: theory and experiment].

Transient Ca2+ and Ca2+-dependent Cl- currents of plasmatic membranes of voltage-clamped Chara corallina freshwater alga cells were studied. Our earlier described method was used for rapid (approximately 10 ms) injection of Ca2+ ions into the cell during the deactivation period of calcium channels following their activation by a positive voltage pulse (injection by "tail" Ca2+ current). This procedure allowed one to determine the amplitude of the Ca2+ component, as well as the amplitude and kinetics of the submembrane Ca2+ concentration-dependent Cl- component for the transient current. Calculations based on the cell model allowing for Ca2+ diffusion, the Ca2+-buffering properties of the cytoplasm, and the nonlinear dependency of iCl on [Ca2+]cyt, as well as the presence of chloroplasts agreed well with the experimentally observed behavior of the transient current. The slow stage of the [Ca2+]cyt relaxation to the resting level (approximately 10(-7) M), related to the functioning of Ca2+-ATPases, was shown to take approximately 10(2) s. We assume this stage to determine the duration of the refractory period after the generation of action potential.

[Effect of avermectns on Ca(2+)-dependent chloride currents in plasmalemma of Chara corallina cells]. / Deistvie avermektinov na Ca(2+)-zavisimyi khlornyi tok plazmalemmy kletok Chara corallina.

A natural complex of avermectins, aversectin C, and a component of this complex, avermectin A1, were shown to change the conductivity of Ca(2+)-dependent chloride channels of plasmalemma of Chara corallina cells by acting only from the outer side of the cellular membrane. Low concentrations of aversectin C and avermectin A1 increased the chloride current: K1/2 = 3.5 x 10(-5) mg/ml for the whole complex and K1/2 = 2.1 x 10(-3) mg/ml for A1. Relatively high concentrations of the compounds suppressed the chloride current: K1/2 = 2.2 x 10(-3) mg/ml for aversectin C and K1/2 = 4.2 x 10(-6) mg/ml for A1. The Hill coefficients for the interaction of avermectin A1 with the corresponding targets for stimulation and suppression of the chloride current were 2.8 and 2.5 respectively. Bicuculine, a non-specific inhibitor of the GABA alpha-receptors, did not influence stimulation of chloride currents caused by action of low concentrations of avermectins, but at the same time blocked suppression of the chloride currents associated with the action of high doses of avermectins. Avermectins A2, B1 (abamectin), B2 and 22,23-dihydroavermectin B1 (vermectin) in the concentration range studied, did not affect the chloride currents of Chara corallina cells.

Through pore diameter in the cell wall of Chara corallina.

Determination of pore size of the cell wall of Chara corallina has been made by using the polyethylene glycol (PEG) series as the hydrophilic probing molecules. In these experiments, the polydispersity of commercial preparation of PEGs was allowed for. The mass share (gamma(p)) of polyethylene glycol preparation fractions penetrating through the pores was determined using a cellular 'ghost', i.e. fragments of internodal cell walls filled with a 25% solution of non-penetrating PEG 6000 and tied up at the ends. In water, such a 'ghost' developed a hydrostatic pressure close to the cell turgor which persisted for several days. The determination of gamma(p), for polydisperse polyethylene glycols with different average molecular mass (M) was calculated from the degree of pressure restoration after water was replaced by a 5-10% polymer solution. Pressure was recorded using a dynamometer, which measures, in the quasi-isometric mode, the force necessary for the partial compression of the 'ghost' in its small fragment. By utilizing the data on the distribution of PEG 1000, 1450, 2000, and 3350 fractions over molecular mass (M), it was found that gamma(p), for these polyethylene glycols corresponded to the upper limit of ML=800-1100 D (hydrodynamic radius of molecules, r(h)=0.85-1.05 nm). Thus, the effective diameter of the pores in the cell wall of Chara did not exceed 2.1 nm.

Effect of avermectins on Ca2+-dependent Cl- currents in plasmalemma of Chara corallina cells.

A natural complex of avermectins, aversectin C, and a component of this complex, avermectin A1, were shown to change the conductivity of Ca2+-dependent Cl- channels of plasmalemma of Chara corallina cells by acting from the outer side of the cellular membrane. Low concentrations of aversectin C and avermectin A1 increased the Cl- current: K1/2 = 35 ng/ml for the whole complex and K1/2 = 21 pg/ml for A1. Relatively high concentrations of the compounds suppressed the Cl- current: K1/2 = 2.2 microg/ml for aversectin C and K1/2 = 4.2 ng/ml for A1. The Hill coefficient for the interaction of avermectin A1 with the corresponding targets was identical for stimulation and suppression of the Cl- current: 2.8 and 2.5, respectively. Bicuculline, a nonspecific inhibitor of the GABAa receptors, did not influence stimulation of Cl- currents caused by low concentrations of avermectins, but at the same time blocked suppression of the Cl- currents by high concentrations of avermectins. Avermectins A2, B1, B2, abamectin and 22,23-dihydroavermectin B1 (ivermectin) did not affect the Cl- currents of Chara corallina cells.

[Allowing for polymer polydispersity--an essential condition for determination of aqueous pore diameters in cell walls and membranes using polymers]. / Uchet polidispersnosti polimerov--neobkhodimoe uslovie pri opredelenii s ikh pomoshch'iu diametra vodnykh por v kletochnykh obolochkakh i membranakh.

A method of allowing for polydispersion of polyethylene glycol (PEG) preparations was developed for the use of these preparations for the osmometrical evaluation of pore diameters with aqueous pores of Chara corallina cell walls as an example. The mass share of polyethylene glycol preparation fractions gamma p penetrating through the pores was determined using cellular "shadows", fragments of internodal cell walls tied up at the ends and filled with a 25% solution of nonpenetrating PEG 6000. When immersed into water, such "shadow" acquired a turgor (hydrostatic) pressure close to the cellular pressure and persistent over long time. The determination of gamma p for polyethylene glycols with different average molecular weights Mw was performed from the degree of pressure restoration after water was replaced by a 5-10% polymer solution. The kinetics of pressure changes was recorded using a mechanotronic dynamometer, which measures, in the quasi-isometric mode, the force necessary for partial compression of the "shadow" in its small fragment. By utilizing the dependence of the overall share of fractions with molecular weights Mi < Mk on Mk (data of [1]), we found that gamma p, for these polyethylene glycols corresponds to the threshold value of Mk = 800-1100 D (hydrodynamic radius of molecules rh = 0.85-1.05 nm). Thus, the effective diameter of the pores in the cell wall of Chara does not exceed 2.1 nm. It was shown that the smoothness of the sigmoid shape of the dependence of ionic channel conductivity on the Mw value of the polymer in the media is largely due to the polydispersion of polymer preparations, particularly, to the reduction in the share of fractions penetrating the channels as Mw is increased. The method normally used to estimate pore diameters in ionic channels which ignores the dispersion of polymer preparations, results in overestimated values.

D2O-induced ion channel activation in Characeae at low ionic strength.

Effects of D2O were studied on internodal cells of the freshwater alga Nitellopsis obtusa under plasmalemma perfusion (tonoplast-free cells) with voltage clamp, and on Ca2+ channels isolated from the alga and reconstituted in bilayer lipid membranes (BLM). External application of artificial pond water (APW) with D2O as the solvent to the perfused plasmalemma preparation led to an abrupt drop of membrane resistance (Rm = 0.12 +/- 0.03 k omega.cm2), thus preventing further voltage clamping. APW with 25% D2O caused a two-step reduction of Rm: first, down to 2.0 +/- 0.8 k omega.cm2, and then further to 200 omega.cm2, in 2 min. It was shown that in the first stage, Ca2+ channels are activated, and then, Ca2+ ions entering through them activate the Cl- channels. The Ca2+ channels are activated irreversibly. If 100 mM CsCl was substituted for 200 mM sucrose (introduced for iso-osmoticity), no effect of D2O on Rm was observed. Intracellular H2O/D2O substitution also did not change Rm. In experiments on single Ca2+ channels in BLM H2O/D2O substitution in a solution containing 100 mM KCl (trans side) produced no effect on channel activity, while in 10 mM KCl, at negative voltage, the open channel probability sharply increased. This effect was irreversible. The single channel conductance was not altered after the H2O/D2O substitution. The discussion of the possible mechanism of D2O action on Ca2+ and Cl- channels was based on an osmotic-like stress effect and the phenomenon of higher D-bond energy compared to the H-bond.

[The effect of charged local anesthetics on the inactivation of Ca2+-activated Cl-channels of characean algae]. / Vliianie zapiazhennykh mestnykh anestetikov na inaktivatsiiu Ca-2+-aktiviruemykh Cl-analov kharovoi vodorosli.

Effects of local anesthetics (LA) and a number of organic cations on Ca2+-activated Cl-channels in plasmalemma of intracellularly perfused giant algae Nitellopsis obtusa were studied using voltage-clamp technique. It was shown earlier that Ca2+ ions cause irreversible inactivation of Cl-channels with a characteristic time equal to a few minutes, but not only activate Cl-channels. It has been found that amphiphilic cations (AC), including LA+, introduced intracellularly together with Ca2+ produced delayed action on the beginning of the inactivation process (approximately ten minutes) producing no effect on activation during this period. The time of delayed action was linearly dependent on the concentrations ratio alpha = [AC]/[Ca2+]. Procaine is the most effective agent in this respect, the time of its delayed action on the inactivation process being 20 min at alpha = 1. LA in the neural form, hydrophilic AC of tetraethylammonium, as well as LA+ from the outside had no effect on Cl-channels. Cl-channels inactivated "irreversibly" by Ca2+ ions may be restored after addition of AC in Ca2+-containing perfusion medium.

Ca2+-induced activation and irreversible inactivation of chloride channels in the perfused plasmalemma of Nitellopsis obtusa.

Experiments were carried out on the algal cells with removed tonoplast using both continuous intracellular perfusion and voltage clamp on plasmalemma. The transient plasmalemma current induced by depolarization disappeared upon perfusion with the Ca2+-chelating agent, EGTA, since the voltage-dependent calcium channels lost their ability to activate. Subsequent replacement of the perfusion medium containing EGTA by another with Ca2+ for clamped plasmalemma (-100 mV) induced an inward C1- current which showed both activation and inactivation. The maximal amplitude of the current at [C1-]in = 15 mmol/l (which is similar to that in native cells) was approximately twice that in electrically excited cell in vivo. The inactivation of C1 channels in the presence of internal Ca2+ was irreversible and had a time constant of 1-3 min. This supports our earlier suggestion (Lunevsky et al. 1983) that the inactivation of C1 channels in an intact cell (with a time constant of 1-3 s) is due to a decrease in Ca2+ concentration rather than to the activity of their own inactivation mechanism. The C1 channel selectivity sequence was following: C1- much greater than CH3SO-4 approximately equal to K+ much greater than SO2-4 (PK/PSO4 approximately 10). Activation of one half the channels occurs at a Ca2+ concentration of 2 X 10(-5) mol/l. Sr2+ also (though to a lesser extent) activated C1 channels but had to be present in a much more higher concentration than Ca2+. Mg2+ and Ba2+ appeared ineffective. Ca2+ activation did not, apparently, require participation of water-soluble intermediator including ATP. Thus, C1 channel functioning is controlled by Ca2+-, Sr2+-sensitive elements of the subplasmalemma cytoskeleton.