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G N Berestovsky

Publications and source records attributed to G N Berestovsky.

10 recordsLinked to original sources
PubMed2001

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.

Calcium↗
PubMed2001

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.

Biomechanical Phenomena↗
PubMed1998

Effective diameter and structural organization of reconstituted calcium channels from the Characeae algae Nitellopsis.

Using hydrophilic non-electrolytes, we determined the effective diameter of calcium channels from the Characeae alga Nitellopsis, reconstituted in a planar lipid membrane. It is suggested that a "single" reconstituted channel is a cluster consisting of several protochannels, in which the channel-forming molecules are stabilized by calcium ions. It is shown that the channels assembled in a cluster with the common conductivity of 350 pS (in 0.1 M KCl) have a funnel-like structure. The diameter of the smaller section is 0.96 +/- 0.20 nm, the diameter of the wider vestibule is 1.78 +/- 0.30 nm. Similarity of the structural organization of the channels investigated to the channels formed by annexin proteins is discussed.

Action Potentials↗
PubMed1997

Effective diameters of ion channels formed by homologs of the antibiotic chrysospermin.

Radii of ion channels formed in the lipid bilayer by 4 homologs of the alamethicin-like antibiotic, chrysospermin, were determined using hydrophilic nonelectrolytes. It is shown that the replacement of isovaline amino acid at position 15 of the polypeptide chain by alpha-aminoisobutyric acid results in the decrease in the channel effective radius from 1.2 +/- 0.15 to 0.94 +/- 0.1 nm and a respective 2.5-fold decrease in channel conductance.

Amino Acid Sequence↗
PubMed1994

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.

Calcium Channels↗
PubMed1993

Effects of D2O on permeation and gating in the Ca(2+)-activated potassium channel from Chara.

We studied the effects of H2O/D2O substitution on the permeation and gating of the large conductance Ca(2+)-activated K+ channels in Chara gymnophylla droplet membrane using the patch-clamp technique. The selectivity sequence of the channel was: K+ > Rb+ >> Li+, Na+, Cs+ and Cl-. The conductance of this channel in symmetric 100 mM KCl was found to be 130 pS. The single channel conductance was decreased by 15% in D2O as compared to H2O. The blockade of channel conductance by cytosolic Ca2+ weakened in D2O as a result of a decrease in zero voltage Ca2+ binding affinity by a factor of 1.4. Voltage-dependent channel gating was affected by D2O primarily due to the change in Ca2+ binding to the channel during the activation step. The Hill coefficient for Ca2+ binding was 3 in D2O and around 1 in H2O. The values of the Ca2+ binding constant in the open channel conformation were 0.6 and 6 microM in H2O and D2O, respectively, while the binding in the closed conformation was much less affected by D2O. The H2O/D2O substitution did not produce a significant change in the slope of channel voltage dependence but caused a shift as large as 60 mV with 1 mM internal Ca2+.

Calcium↗
PubMed1984

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.

Calcium↗
PubMed1978

Voltage-induced reflectivity relaxation of bilayer lipid membranes: on changes of bilayer thickness.

Temporal and voltage-induced changes of reflectivity (R), the optical phase difference in transmitted polarized light, of tension and total capacity of bilayer lipid membrane (BLM) were studied. The membranes were mainly formed from total brain phospholipids (TP) in n-alkanes. 1) Reflectivity of "black" regions of films made of TP in decane and hexadecane decreases by several percent with a time constant (tauR) of about 30 min, whereas that of membranes with hexane and heptane does not depend on time (with an accuracy up to 1--2%). The BLM tension decreases appreciably in the course of time and reaches its steady-state value in tens of minutes after complete blackening of the membrane. 2) Under prolonged (up to tens of minutes) action of voltage (V) no R changes of BLMs with hexane, heptane, and hexadecane were revealed at a noise level of 0.2%. Blms with decane usually respond to voltage application, first by a rapid (jump-like) and then by a slow decrease of R with a value spread from 0.2% to 3%. 3) With higher amplitude and temporal resolutions of the signal (signal averaging method) it can be seen that after voltage jump R decreases down to a new steady-state value: at V = 100 mV, deltaR/R = -(2--4) . 10(-4) and tauR approximately 0.1 msec for BLMs from TP in heptane, and deltaR/R = -(3--6) . 10(-2) and tauR approximately 2 msec for BLMs from oxidized cholesterol in decane. It is shown in the latter case that the great value of deltaR/R is due to the contribution of invisible microlenses. In all the cases deltaR approximately V2. 4) It is concluded that at voltage jump a bilayer first becomes thinner due to volumic compression of its hydrocarbon core; then it spreads with a time constant of the order of 0.1 msec, getting thinner until a new equilibrium state is reached. Complete change of bilayer thickness is detah/h approximately -10(-4) at 100 mV.

Alkanes↗