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V A Derkach

Publications and source records attributed to V A Derkach.

At least 19 recordsLinked to original sources
PubMed2000

Postsynaptic protein phosphorylation and LTP.

Prolonged changes in synaptic strength, such as those that occur in LTP and LTD, are thought to contribute to learning and memory processes. These complex phenomena occur in diverse brain structures and use multiple, temporally staged and spatially resolved mechanisms, such as changes in neurotransmitter release, modulation of transmitter receptors, alterations in synaptic structure, and regulation of gene expression and protein synthesis. In the CA1 region of the hippocampus, the combined activation of SRC family tyrosine kinases, protein kinase A, protein kinase C and, in particular, Ca2+/calmodulin-dependent protein kinase II results in phosphorylation of glutamate-receptor-gated ion channels and the enhancement of subsequent postsynaptic current. Crosstalk between these complex biochemical pathways can account for most characteristics of early-phase LTP in this region.

Animals↗
PubMed1995

Identification of a Ca2+/calmodulin-dependent protein kinase II regulatory phosphorylation site in non-N-methyl-D-aspartate glutamate receptors.

Glutamate receptor ion channels are colocalized in postsynaptic densities with Ca2+/calmodulin-dependent protein kinase II (CaM-kinase II), which can phosphorylate and strongly enhance non-N-methyl-D-aspartate (NMDA) glutamate receptor current. In this study, CaM-kinase II enhanced kainate currents of expressed glutamate receptor 6 in 293 cells and of wild-type glutamate receptor 1, but not the Ser-627 to Ala mutant, in Xenopus oocytes. A synthetic peptide corresponding to residues 620-638 in GluR1 was phosphorylated in vitro by CaM-kinase II but not by cAMP-dependent protein kinase or protein kinase C. The 32P-labeled peptide map of this synthetic peptide appears to be the same as the two-dimensional peptide map of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) glutamate receptors phosphorylated in cultured hippocampal neurons by CaM-kinase II described elsewhere. This CaM-kinase II regulatory phosphorylation site is conserved in all AMPA/kainate-type glutamate receptors, and its phosphorylation may be important in enhancing postsynaptic responsiveness as occurs during synaptic plasticity.

Amino Acid Sequence↗
PubMed1994

Mechanism of long-lasting block of ganglion nicotinic receptors by mono-ammonium compounds with long aliphatic chain.

The effect of long-chain mono-ammonium compounds (long-chain MACs), t-butyldecylammonium (IEM-1078), 2,2,6,6-tetramethyldecylpiperidine (IEM-1559), and diisopropyldecylammonium (IEM-1194), on nicotinic acetylcholine receptors (nAChRs) was studied in sympathetic ganglion neurons using the patch clamp method. Long-chain MACs (1-10 microM) strongly inhibited acetylcholine (ACh)-induced current (ACh-current); the block persisted for hours after washing the drugs out. Short-chain MACs had a much weaker and completely reversible blocking effect. Suppression of ACh-current by MACs was dose- and voltage-dependent; it was absent at low ACh doses or at potentials > or = 60 mV and increased with higher ACh doses or hyperpolarization. The second of two ACh-currents induced by paired application of ACh was inhibited by long-chain MACs more strongly than the first. This use-dependent block also persisted for hours after washing the drugs out. Additional inhibition of the second ACh-current was reduced by lengthening the time interval between ACh applications in the pair. Time constants of the recovery of the second ACh-current in the presence and after washing out of long-chain MACs were similar, ranging from 45 to 140 s at -50 mV for different long-chain MACs, and decreased with de- or hyperpolarization. The use-dependent block produced by long-chain MACs could be prevented by another long-chain MAC with a small ammonium head (IEM-1195, 75-100 microM) or trimethaphan (30 microM), a competitive antagonist of ACh in ganglia. Neither the short-chain MAC (IEM-1405, 100 microM) nor ACh (100 microM) could exert this protective effect. Long-chain MACs did not exert any use-, dose- or voltage-dependent suppression of ACh-current when applied intracellularly. Single-channel conductance was not affected by IEM-1194 (3-10 microM). We suggest that inhibition of ACh-current by long-chain MACs is accounted for by (i) a long-lasting, apparently irreversible, binding of the drug near the channel of nAChR via its long aliphatic chain and (ii) a slow reversible block of the nAChR channel with the MAC's ammonium head.

Acetylcholine↗
PubMed1991

Role of disulphide bonds in burst-like activity of nicotinic acetylcholine receptor channels in rat sympathetic neurones.

1. The effects of reduction of disulphide bonds in nicotinic acetylcholine receptors (nicotinic AChRs) with dithiothreitol (DTT) were studied in rat superior cervical ganglion neurones using the patch-clamp method in whole-cell and cell-attached recording modes. 2. Dithiothreitol (1 mM) markedly reduced the ACh-induced membrane current, while the action of ACh remained reversible. Conversely, bromoacetylcholine (BrACh), if applied after the treatment with DTT, caused irreversible activation of nicotinic AChRs manifested in the appearance of a non-declined steady-state component in BrACh-induced currents accompanied by increased membrane current fluctuations. The successive reoxidation of sulphydryl groups by potassium ferricyanide (1 mM-ferricyanide) restored the response to ACh. Ferricyanide itself had a weaker inhibitory effect on the ACh-induced current, compared to the effect of DTT. 3. As a result of the action of DTT (1 mM), the spectrum of BrACh-induced current noise shifted to a higher frequency range. 4. The distributions of durations of the gaps (closed states) and the bursts (the states identified as open states after the shortest gaps were ignored) in single-channel activity of native (non-treated with DTT) nicotinic AChRs caused by ACh (30 microM) and BrACh (30 microM) were similar and both revealed four to five and two to three components for gap intervals and burst durations respectively. 5. Single-channel behaviour of reduced nicotinic AChRs was similar for both ACh and BrACh as agonists, but significantly differed from that in the native one. The first difference was the marked increase in the frequency of the appearance of long closed states of the channel that was presumably due to enhanced receptor desensitization. The second difference was an almost complete disappearance of long bursts associated with disappearance of the fastest component in gap interval distribution. 6. Mean conductance of single nicotinic AChR channels decreased by approximately 20% in the reduced receptor compared with that in the native one, for both agonists. 7. The results suggest a critical role of disulphide bonds for the functioning of native neuronal nicotinic AChRs: the disruption of disulphide bonds leads to the loss of burst-like kinetics of the nicotinic AChR ionic channel.

Acetylcholine↗
PubMed1988

[Mechanism of action of tubocurarine on nicotinic cholinoreceptors of neurons of the sympathetic ganglia of rats].

Tubocurarine (Tc) effect on membrane currents elicited by acetylcholine (ACh) was studied in isolated superior cervical ganglion neurons of rat using patch-clamp method in the whole-cell recording mode. The "use-dependent" block of ACh current by Tc was revealed in the experiments with ACh applications, indicating that Tc blocked the channels opened by ACh. Mean lifetime of Tc-open channel complex, tau, was found to be 9.8 +/- 0.5 s (n = 7) at -50 mV and 20-24 degrees C. tau exponentially increased with membrane hyperpolarization (e-fold change in tau corresponded to the membrane potential shift by 61 mV). Inhibition of the ACh-induced current by Tc (3-30 microM/1) was completely abolished by membrane depolarization to the level of 80-100 mV. Inhibition of ACh-induced current was augmented at increased ACh doses. It is concluded that the open channel block produced by Tc is likely to be the only mechanism for Tc action on nicotinic acetylcholine receptors in superior cervical ganglion neurons of rat.

Acetylcholine↗
PubMed1988

[The "trap"--a modification of the block of neuronal nicotinic cholinoceptors].

The effect of IEM-1742, a pentaethonium derivative, on the currents induced by iontophoretic applications of acetylcholine was studied in rat superior cervical ganglion neurons using patch-clamp method in the whole-cell modification. Blocking action increased with membrane hyperpolarization and was removed by strong membrane depolarization. Apparent dissociation constant for the receptor-blocker reaction was found to be (2.9 +/- 0.6) 10(-6) M (n = 6) at -50 mV and 20-23 degrees C. IEM-1742 blocks the nicotinic acetylcholine receptor in its activated form. The dissociation of IEM-1742 from the receptor was drastically accelerated during its activation by agonist (trap-block). Trapped receptor was not released from the blocker only by membrane depolarization to the level at which any blocking effect is absent. The data obtained show that IEM-1742 in rat sympathetic ganglion neurons acts in the potential-dependent manner and displays a trap-effect.

Acetylcholine↗
PubMed1988

[The potential dependence of acetylcholine-activated membrane conductance in sympathetic ganglion neurons].

Membrane conductance activated by acetylcholine (ACh-conductance) was studied in rat isolated superior cervical ganglion neurons by means of the patch-clamp method in the whole-cell recording mode. It was found that ACh-conductance was increased or decreased with membrane hyper- or depolarization, respectively. The decrease in ACh-conductance was not associated with the reversal of ACh-current or with the presence of Ca2+ ions in external solution. The time constant of voltage-jump relaxation of ACh-current revealed e-fold increase with membrane hyperpolarization by 70 mV, which corresponded to the voltage dependence of ACh-conductance. Basing upon these results it was concluded that the voltage dependence of ACh-conductance is mostly determined by the voltage dependence of nicotinic receptor channel gating kinetics.

Acetylcholine↗
PubMed1987

Single channels activated by acetylcholine in rat superior cervical ganglion.

1. The elementary currents flowing through single channels opened by acetylcholine were recorded in rat superior cervical ganglion neurones using patch-clamp methods. Acetylcholine (30 microM) was included in the patch electrode (cell-attached recordings) or applied by ionophoresis (outside-out configuration). All measurements were made at 23-25 degrees C and mostly at -110 mV. 2. Channel openings appeared both as single events and as bursts of events. One population of the currents observed had a conductance of 20.0 +/- 0.2 pS (mean +/- S.E. of mean, n = 4). A second population had a conductance of about 50 pS, occurred more rarely, and was not included in further analysis. 3. Four channel closed time periods and two channel open time periods were found from the distributions of closed and open times. It was found that shorter channel openings (about 0.2 ms) appeared in isolation, whereas longer openings (duration 1.3 +/- 0.2 ms, n = 4) appeared as bursts of openings separated by the shortest channel closed time periods (about 0.15 ms). The next shortest closed time (about 2 ms) apparently corresponds to the lifetime of the channel not activated by acetylcholine. The two longer closed times (about 80 ms and 1 s) may reflect desensitization. The mean burst duration was 8.5 +/- 1.2 ms (n = 4), giving about six openings per burst. 4. Because the time constant of decay of the excitatory post-synaptic current is more similar to the burst duration than to the duration of individual single openings, it is suggested that acetylcholine released from presynaptic nerves may result in a burst of openings rather than a single opening. 5. On the basis of the above assumption, the rate constants were calculated for a sequential model in which acetylcholine binds to the receptor (forward rate k + 1 = 2.3 X 10(7) M-1 s-1; reverse rate k-1 = 1235 s-1) which then undergoes a conformational change to an open state (forward rate beta = 6293 s-1; reverse rate alpha = 894 s-1). 6. When heptamethonium (30 microM) was added to the solution in the patch electrode, the burst duration was markedly shortened, but there was no change in the closed time between two openings within the burst. This effect was voltage-dependent, which suggests that heptamethonium binds to the channel after it is opened by acetylcholine.

Acetylcholine↗
PubMed1984

[Ganglionic-blockading action of bis-ammonium compounds].

The actions of bis-ammonium compounds on acetylcholine-activated channels were studied in voltage-clamped neurons of isolated superior cervical ganglion in a rabbit. The kinetics of the compound binding to open channels was estimated from shortening of the decay of fast excitatory postsynaptic current (which is determined by the rate of channels closure). The kinetics of dissociation of the compound from open channels was estimated from the kinetics of the restoration of the second response to double-pulse application of acetylcholine in presence of the blocking compound. The rate constant of bindings of the bis-ammonium compounds to open channels increased while the rate constant of dissociation decreased with membrane hyperpolarization. This voltage-dependence increased with the lengthening of the polymethylene chain in the compound and remained unchanged with the lengthening of nitrogen group radicals. The ganglion-blocking activities of the compounds as determined in the cat ganglion in situ correlated with their rate constants of binding to open channels. It was concluded that ganglion-blocking actions of bis-ammonium compounds is determined by their channel-blocking activities.

Acetylcholine↗
PubMed1983

Channel-blocking activity is a possible mechanism for a selective ganglionic blockade.

The actions of bis-ammonium compounds (BAC) on the ionic channels activated by acetylcholine (ACh) were studied in voltage-clamped neurones of rabbit isolated superior cervical ganglion. The kinetics of binding of BAC to open channels was estimated from shortening of the decay of fast excitatory postsynaptic current. The kinetics of dissociation of BAC from open channels was estimated from the kinetics of restoring of second response to double-pulse application of ACh in presence of BAC. The ganglion-blocking activities of BAC correlated with the rate constants of their binding to open channels. It was concluded that selective ganglion-blocking actions of BAC were determined by their channel-blocking activities.

Acetylcholine↗
PubMed1983

Acetylcholine-induced current fluctuations and fast excitatory post-synaptic currents in rabbit sympathetic neurones.

Post-synaptic currents and responses to ionophoretically applied acetylcholine (ACh) were recorded at 34-37 degrees C from rabbit superior cervical ganglion neurones clamped at -80 mV membrane potential. Atropine (1 microM) was used to block muscarinic receptors. The fast excitatory post-synaptic current (e.p.s.c.) reversed at -9.6 +/- 1.7 mV and decayed with a single exponential time course. The e.p.s.c. decay time constant, tau d, was 4.5 +/- 0.3 msec and increased as the membrane was hyperpolarized (e-fold increase in tau d corresponded to 140 mV hyperpolarization). Miniature e.p.s.c.s. (m.e.p.s.c.s) decayed with time constants similar to those of the e.p.s.c. The decay of the e.p.s.c. was slowed by lowering temperature but remained a single exponential; the changes of tau d with temperature followed the Arrhenius equation (Q10 = 3.7). In most of the neurones studied the analysis of ACh noise spectra revealed two kinetic components with mean time constants tau N1 = 1.1 +/- 0.1 msec and tau N2 = 5.0 +/- 0.5 msec. In a few neurones only the tau N1 component was found. Similar two-component ACh noise spectra were observed in the neurones not treated with atropine. tau N1 and tau N2 components revealed temperature dependences similar to each other and close to that of tau d. The values of tau N1 and tau N2 and the ratio between the contributions of the tau N1 and tau N2 components to the ACh noise spectrum did not depend on the dose of ACh. The single channel conductance is 36 +/- 3 pS. A single ACh quantum opens about 150 ionic channels and the e.p.s.c. consists of 4-243 quanta. It is suggested that in mammalian sympathetic ganglion neurones there are two types of nicotinic ACh receptor channels, with short and long lifetimes, and that the kinetics of e.p.s.c. and m.e.p.s.c. are determined by the activity of the longer lifetime channel type.

Acetylcholine↗
PubMed1982

Two modes of activity of nicotinic acetylcholine receptor channels in sympathetic neurons.

Spectral analysis of acetylcholine (ACh) noise was performed in voltage-clamped neurons of the isolated rabbit superior cervical ganglion at 34-37 degrees C and at membrane potential--80 mV. Two modes of activity were found in the ionic channels of nicotinic ACh receptors, with mean channel life-times of for fast-operating channels and for slow-operating channels. Excitatory postsynaptic current (EPSC) decays exponentially with a time constant which is very close to , indicating that the slow-operating channel activity determines the duration of EPSC. The mean value of conductance of single nicotinic ACh-receptor channel is 36 more or less 3 pS.

Acetylcholine↗
PubMed1982

Voltage-dependent actions of short-chain polymethylene bis-trimethylammonium compounds on sympathetic ganglion neurons.

Effects of polymethylene bis-trimethylammonium compounds (with 4-7 carbons in the polymethylene chain, C4-C7) on voltage-dependence of fast excitatory postsynaptic current (EPSC) were studied in voltage-clamped neurons of the isolated rabbit superior cervical ganglion. All these compounds shortened the EPSC decay (which remained single-exponential) and decreased (or reversed) the dependence of the EPSC decay on membrane hyperpolarization. All drugs slightly decreased the EPSC amplitude; in addition, C6 and C7 decreased their dependence on membrane hyperpolarization. It is suggested that shortening of the EPSC decay produced by ganglion-blocking agents results from their binding to the open ionic channel (channel-blocking effect). The ratio of channel-blocking activities of these drugs correlates with the well-known ratio of their ganglion-blocking activities. It is suggested that the channel-blocking activities of polymethylene bis-trimethylammonium compounds determine their ganglion-blocking activities. The model of channel-blocking action is discussed.

Animals↗
PubMed1982

Distribution of muscarinic receptors in mammalian sympathetic ganglion: autoradiographic and electrophysiological studies.

Localization of muscarinic receptors in rabbit superior cervical ganglion (SCG) neurons was investigated by means of light microscopy autoradiographic study of binding sites for the labeled selective muscarinic antagonist atropine, and intracellular recordings were made from single ganglionic neurons to determine their response to local iontophoretic application of the selective muscarinic agonist--5-methylfurmethide (MF). Autoradiography showed that muscarinic receptors are located predominantly on the dendrites of ganglion neurons and on their soma near large processes. The remaining soma areas are usually devoid of muscarinic receptors or their density is much lower than in dendritic areas. MF-elicited depolarization was seen in 34% of neurons studied; an initial hyperpolarization was followed by depolarization in 23% of the neurons and no responses occurred in the remaining 43%. Lowering Ca2+ and increasing Mg2+ content in the external medium abolished MF-hyperpolarization but not MF-depolarization. The following properties of MF-depolarization support the concept of dendritic localization of muscarinic receptors: (i) the time-course of MF-depolarization varies widely in different cells; (ii) its rise time increases with the increase of the MF dose; (iii) MF is more effective in inducing a MF-depolarization if it is applied to cell processes than if it is applied to cell soma. The origin of MF-hyperpolarization is discussed.

Animals↗
PubMed1979

Fast excitatory postsynaptic currents in voltage-clamped mammalian sympathetic ganglion neurones.

Fast excitatory postsynaptic currents (EPSCs) were recorded in voltage-clamped neurones of isolated superior cervical ganglion of the rabbit. The rise time, decay time and whole duration of EPSC, as well as miniature EPSC, were shorter than those of corresponding postsynaptic potentials. Characteristic impedance for EPSC was 5.5 +/- 1.1 M omega, and was a few times lower than for current evoked by iontophoretic application of ACh. The rise time of EPSC was 2.0 +/- 0.2 msec, the time constant of decay was 3.6 +/- 0.5 msec, and the mean amplitude of EPSC was -5.5 +/- 1.0 nA at the resting potential level (-53.8 +/- 1.4 mV) and at 36 degrees C. Amplitude of EPSC varied with membrane potential almost linearly at negative potentials, non-linearly at positive potentials, and nullified at -8.9 +/- 1.8 mV. The decay of EPSC was exponential over the most of its time course and the rate constant of decay (alpha) varied exponentially with membrane potential according to the relationship alpha(V) = B exp(AV), with A = 0.00716 +/- 0.00101 mV-1 and B = 0.46 +/- 0.07 msec-1. The voltage sensitivity of EPSC decay is interpreted in terms of voltage sensitivity in ionic channel lifetimes.

Animals↗