PubMed Health⌕ Search

Biomedical subjects

S I Alekseev

Publications and source records attributed to S I Alekseev.

At least 19 recordsLinked to original sources
PubMed1999

Effects of millimeter waves on ionic currents of Lymnaea neurons.

The effects of mm-waves 60.22-62.22 GHz and 75 GHz on A-type K+ currents and the effects of 61.22 GHz on Ca2+ currents of Lymnaea neurons were investigated using a whole-cell voltage-clamp technique. The open end of a rectangular waveguide covered with a thin Teflon film served as a radiator. Specific absorption rates at the waveguide outlet, inserted into physiological solution, were in the range of 0-2400 W/kg. Millimeter wave irradiation increased the peak amplitudes, activation rates, and inactivation rates of both ion currents. The changes in A-type K+ current were not dependent on the irradiation frequency. It was shown that the changes in the amplitudes and kinetics of both currents resulted from the temperature rise produced by irradiation. No additional effects of irradiation on A-type K+ current other than thermal were found when tested at the phase transition temperature or in the presence of ethanol. Ethanol reduced the thermal effect of irradiation. Millimeter waves had no effect on the steady-state activation and inactivation curves, suggesting that the membrane surface charge and binding of calcium ions to the membrane in the area of channel locations did not change.

Absorption↗
PubMed1997

Millimeter waves thermally alter the firing rate of the Lymnaea pacemaker neuron.

The effects of millimeter waves (mm-waves, 75 GHz) and temperature elevation on the firing rate of the BP-4 pacemaker neuron of the pond snail Lymnaea stagnalis were studied by using microelectrode techniques. The open end to a rectangular waveguide covered with a thin Teflon film served as a radiator. Specific absorption rates (SARs), measured in physiological solution at the radiator outlet, ranged from 600 to 4,200 W/kg, causing temperatures rises from 0.3 to 2.2 degrees C, respectively. Irradiation at an SAR of 4200 W/kg caused a biphasic change in the firing rate, i.e., a transient decrease in the firing rate (69 +/- 22% below control) followed by a gradual increase to a new level that was 68 +/- 21% above control. The biphasic changes in the firing rate were reproduced by heating under the condition that the magnitude (2 degrees C) and the rate of temperature rise (0.96 degrees C/s) were equal to those produced by the irradiation (for an SAR of 4,030 W/kg). The addition of 0.05 mM of ouabain caused the disappearance of transient responses of the neuron to the irradiation. It was shown that the rate of temperature rise played an important role in the development of a transient neuronal response. The threshold stimulus for a transient response of the BP-4 neuron found in warming experiments was a temperature rise of 0.0025 degrees C/s.

Animals↗
PubMed1997

Effects of alcohols on A-type K+ currents in Lymnaea neurons.

The effects of short-chain alcohols (methanol, ethanol and n-propanol) on the fast-inactivating, A-type, potassium current of Lymnaea neurons were examined using macroscopic recording techniques. Alcohols produced a blockade of the current and modified its inactivation mechanism. The extracellular concentrations of methanol, ethanol and n-propanol causing 50% suppression of the current were 2970, 830 and 230 mM, respectively. The main effects of alcohols on inactivation were a decrease in the amplitude of the fast component and a simultaneous increase in the amplitude of the slow component of inactivation. In a model, the suppression of the fast component could be reproduced by an increase of the backward rate constant related to the dissociation of the inactivation particle from its binding site. The blockade and modification of inactivation reveal similar dependences on ethanol concentration, indicating that the same type of interaction of ethanol with the channel underlies both of these events. Ethanol was effective only in extracellular applications. The data support an action of alcohols at a hydrophobic site near the extracellular portion of the channel.

Alcohols↗
PubMed1995

Millimeter microwave effect on ion transport across lipid bilayer membranes.

The effects of millimeter microwaves in the frequency range of 54-76 GHz on capacitance and conductance of lipid bilayer membranes (BLM) were studied. Some of the membranes were modified by gramicidin A and amphotericin B or by tetraphenylboron anions (TPhB-). The millimeter microwaves were pulse-modulated (PW) at repetition rates ranging from 1 to 100 pps, PW at 1000 pps, or unmodulated continuous waves (CW). The maximum output power at the waveguide outlet was 20 mW. It was found that CW irradiation decreased the unmodified BLM capacitance by 1.2% +/- 0.5%. At the same time, membrane current induced by TPhB- transport increased by 5% +/- 1%. The changes in conductance of ionic channels formed by gramicidin A and amphotericin B were small (0.6% +/- 0.4%). No "resonance-like" effects of mm-wave irradiation on membrane capacitance, ionic channel currents, or TPhB- transport were detected. All changes in membrane capacitance and currents were independent of the modulation employed and were equivalent to heating by approximately 1.1 degrees C.

Amphotericin B↗
PubMed1995

Two types of A-channels in Lymnaea neurons.

The gating mechanism of A-channels of Lymnaea neurons and the effect of tetraethylammonium (TEA) on these channels were studied using macroscopic recording techniques. Along with the fast-inactivating A-current (Iaf) described earlier we found a slow-inactivating A-current (Ias) in some neurons of the visceral ganglion. Both currents have revealed similar activation kinetics, but differ in the inactivation kinetics and mechanisms. The inactivation kinetics of Ias were satisfactorily described by a sum of two exponentials with rate constants (tau -1) of 28 s-1 and 4.5 s-1 at V = -20 mV. Intracellular TEA reduced the peak amplitudes of Iaf and Ias and slowed the rate of the fast phase of inactivation of Iaf. This resulted in a crossover of the current traces in the presence and absence of TEA, as though it competes with the binding of the inactivating particle. The mechanism of the fast phase of inactivation of Iaf is similar to that of fast inactivation of the Shaker K+ channels which appears to be due to a ball-and-chain mechanism. The slow phases of inactivation of Iaf and Ias reveal properties characteristic of C-type inactivation shown in Shaker K+ channels. A partially coupled model including three pathways for transition of a channel from the closed to open states accurately reproduces all of the experimental data. It has voltage-independent transitions to the inactivation states indicating that inactivation of A-current is not associated with charge movement through the membrane. The results suggest that Lymnaea A-channels seem to be heteromultimeric.

Action Potentials↗
PubMed1994

Influence of microwaves on different types of receptors and the role of peroxidation of lipids on receptor-protein shedding.

The effects of a continuous wave or pulse-modulated, 900 MHz microwave field were studied by in vitro assays of rat chemoreceptors. The pulsed field was modulated as rectangular waves at rates of 1, 6, 16, 32, 75, or 100 pps. The pulse-period to pulse-duration ratio was 5 in all cases, and specific absorption rates (SARs) ranged from 0.5 to 18 W/kg. Binding of ligands to cell membranes was differentially affected by exposure to microwaves. For example, binding of H3-glutamic acid to hippocampal cells was not altered by a 15 min exposure to a continuous wave field at 1 W/kg, but binding of H3-dihydroalprenolol to liver-cell membranes of neonates underwent a fivefold decrease under the same field conditions. This effect was not dependent on modulation or on a change in the constant of stimulus-receptor binding but depended on a shedding of the membrane's receptor elements into solution. The magnitude of inhibition correlated with the oxygen concentration in the exposed suspension. Antioxidants (dithiothreitol and ionol) inhibited the shedding of receptor elements. The microwave exposure did not cause an accumulation of products from the peroxidation of lipids (POL). Ascorbate-dependent or non-enzymatic POL was not responsible for the inhibition, and POL was not found in other model systems. However, enzymatic POL mechanisms in localized areas of receptor binding remain a possibility.

Animals↗
PubMed1993

Kinetic study of A-type current inactivation in Lymnaea neurons.

Macroscopic inactivation of A-current was studied in internally perfused Lymnaea neurons under voltage clamp conditions. Inactivation kinetics were satisfactorily described by the sum of two exponentials, suggesting the presence of two type inactivation. The kinetics of recovery from inactivation were exponential. The rate constants of the fast phase of inactivation gamma f(V) rose steeply with depolarization exposing the pronounced plateau in the range from -30 to 0 mV. The time course of inactivation in this potential range was more closely approximated with the sum of three exponentially decaying components. Calcium and hydrogen ions strongly affected the fast phase of inactivation. Calcium gave a positive shift of a part of the gamma f(V) curve on the left of the plateau. Raising the pH caused a negative shift of the right-hand branch of the gamma f(V) curve. It was shown that these effects are associated with Ca2+ and H+ binding to some specific sites of the channel protein. Two models give good fits with the experimental data. They include two pathways for fast inactivation. Calcium and hydrogen ions are assumed to selectively affect the voltage-dependent transitions related to these pathways of inactivation.

Animals↗
PubMed1992

Interaction of sulfhydryl reagents with A-type channels of Lymnaea neurons.

The effect of sulfhydryl reagents on macroscopic inactivation of A-current in internally perfused Lymnaea neurons under voltage-clamp conditions was investigated. It was found that the binding of Hg2+ rather than PHMB with channel proteins resulted in a strong decrease of the peak current and the inactivation rate. Hg2+ markedly influenced the steady-state inactivation but did not change the rate of recovery from inactivation. It was found that both reagents reacted with the same groups of the channel protein and that those are most likely sulfhydryl groups. These groups seemed not to be involved in the gating charge movement. Hg2+ ions can immobilize some part of the gating charge thereby resulting in strong changes of the steady-state inactivation.

Animals↗
PubMed1992

Bursting responses of Lymnea neurons to microwave radiation.

Microelectrode and voltage-clamp techniques were modified to record spontaneous electrical activity and ionic currents of Lymnea stagnalis neurons during exposure to a 900-MHz field in a waveguide-based apparatus. The field was pulse-modulated at repetition rates ranging from 0.5 to 110 pps, or it was applied as a continuous wave (CW). When subjected to pulsed waves (PW), rapid, burst-like changes in the firing rate of neurons occurred at SARs of a few W/kg. If the burst-like irregularity was present in the firing rate under control conditions, irradiation enhanced its probability of occurrence. The effect was dependent on modulation, but not on modulation frequency, and it had a threshold SAR near 0.5 W/kg. CW radiation had no effect on the firing rate pattern at the same SAR. Mediator-induced, current activation of acetyl-choline, dopamine, serotonin, or gamma-aminobutyric-acid receptors of the neuronal soma was not altered during CW or PW exposures and, hence, could not have been responsible for the bursting effect.

Animals↗
PubMed1988

Microwave effect on camphor binding to rat olfactory epithelium.

Microwave radiation decreased specific camphor binding to a membrane fraction of rat epithelium but not to a Triton X-100 extract of this fraction. Inhibition of the ligand binding did not depend on the modulation frequency of the microwave field in the region 1-100 Hz and was not a linear function of specific absorption rate (SAR). The decreased ligand binding was due to a shedding or release of the specific camphor-binding protein from the membrane into solution. It is highly probable that several other membrane proteins may be shed into solution during microwave exposure.

Animals↗
PubMedDate not supplied

[Interaction of rhodopsin with quinone].

The reaction of rodopsin extracted with cetyltrimethylammonium bromide with p-benzoquinone was studied with spectrophotometric and ESR methods. In the dark quinone reacted with three SH-groups of rodopsin, in the light with three more SH- and two unknown groups of decolourized rodopsin. The interaction of quinone with SH-groups liberated under light effect on rodopsin proceeds with the formation of intermediate free-radical products.

Animals↗
PubMedDate not supplied

[Effect of electromagnetic radiation in a decimeter wave-length range on the calcium current of molluscan neurons].

Microwave effect on calcium current of the dialysed snail neurons was investigated. Isolated neurons were irradiated by unmodulated and modulated microwaves (900 MHz) with modulation frequency 0,5 divided by 1000 Hz and SAR = 0,1 divided by 20 W/kg. Calcium current increase was shown to be induced by microwave heating. The current increments were proportional to SAR. Microwave effects on the charge distribution of the cell membrane surface and other non-thermal special microwave effects were not detected.

Animals↗