Biomedical subjects

Oleg Krishtal

Publications and source records attributed to Oleg Krishtal.

6 recordsLinked to original sources

PubMed2005

Acid sensing ionic channels: modulation by redox reagents.

Acid-sensing ion channels (ASICs) are widely expressed in mammalian sensory neurons and supposedly play a role in nociception and acid sensing. In the course of functioning the redox status of the tissue is subjected to changes. Using whole-cell patch-clamp/concentration clamp techniques we have investigated the effect of redox reagents on the ASIC-like currents in the sensory ganglia and hippocampal neurons of rat. The reducing agent dithiothreitol (DTT), when applied in the concentrations 1-2 mM, reversibly potentiates proton-activated currents, while the oxidizing reagent 5,5'-dithio-bis-(2-nitrobenzoic acid) (DTNB) causes their inhibition. The EC50 and Hill coefficient for the activation of ASIC-like currents by protons are not affected by DTT. Redox modulation of proton-activated currents is independent on the membrane potential and on the level of pH used for the current activation. The endogenous antioxidant tripeptide glutathione (its reduced form, g-l-glutamyl-l-cysteinyl-glycine, GSH) also potentiates proton-activated currents. Our results indicate that ASIC-like currents are susceptible to regulation by redox agents.

Acid Sensing Ion Channels↗

PubMed2005

Novel spider toxin slows down the activation kinetics of P-type Ca2+ channels in Purkinje neurons of rat.

We have identified a novel polypeptide toxin (Lsp-1) from the venom of the spider Lycosa (LS). Its effect has been examined on the P-type calcium channels in Purkinje neurons, using whole-cell patch-clamp. This toxin (at saturating concentration 7 nM) produces prominent (four-fold) deceleration of the activation kinetics and partial (71+/-6%) decrease of the amplitude of P-current without affecting either deactivation or inactivation kinetics. These effects are not use-dependent. They are partially reversible within a minute upon the wash-out of the toxin. Intracellular perfusion of Purkinje neurons with 100 microM of GDP or 2 microM of GTPgammaS, as well as strong depolarising pre-pulses (+100 mV), do not eliminate the action of Lsp-1 on P-channels indicating that down-modulation via guanine nucleotide-binding proteins (G-proteins) is not involved in the observed phenomenon. In view of extremely high functional significance of P-channels, the toxin can be suggested as a useful pharmacological tool.

Animals↗

PubMed2004

Methyllycaconitine, alpha-bungarotoxin and (+)-tubocurarine block fast ATP-gated currents in rat dorsal root ganglion cells.

The effects of nicotinic acetylcholine receptor antagonists were studied on currents evoked by application of ATP to rat isolated dorsal root ganglion cells, and human embryonic kidney 293 cells expressing rat P2X(3) and P2X(2/3) receptors. The rapidly desensitising (within 100 ms) current in dorsal root ganglion cells was inhibited by methyllycaconitine, alpha-bungarotoxin and (+)-tubocurarine (concentrations giving half-maximal inhibition were approximately 40, 60 and 800 nm, respectively), but not by hexamethonium (100 microm) or mecamylamine (100 microm). The sustained (>250 ms) current in dorsal root ganglion cells was inhibited by (+)-tubocurarine (80% by 10 microm), but not by methyllycaconitine (200 nm), alpha-bungarotoxin (200 nm), mecamylamine (100 microm) or hexamethonium (100 microm). Rapidly desensitising currents evoked by alpha,betamethylene-ATP in human embryonic kidney cells expressing P2X(3) receptors were inhibited by methyllycaconitine and alpha-bungarotoxin, at concentrations similar to those effective in dorsal root ganglion cells. The results indicate that some nicotinic acetylcholine receptor antagonists are potent blockers of P2X receptors on neurons, particularly the homo-oligomeric P2X(3) receptor. This finding suggests that these drugs should be used with care to discriminate between P2X and neuronal acetylcholine receptor types.

Aconitine↗

PubMed2004

Protective cap over CA1 synapses: extrasynaptic glutamate does not reach the postsynaptic density.

Numerous data indicate that nonsynaptic release of glutamate occurs both in normal and pathophysiological conditions. When reaching receptors in the postsynaptic density (PSD), glutamate (Glu) could affect the synaptic transmission. We have tested this possibility in the hippocampal CA1 synapses of rats, either by applying exogenous Glu to the CA1 neurons or by disruption of Glu transporter activity. L-Glu (400 microM) was directly applied to the hippocampal slices acutely isolated from the rats. It produced a strong inhibition of both ortho- and antidromically elicited action potentials fired by CA1 neurons while the excitatory postsynaptic current (EPSC) measured in these neurons remained totally unaffected. The optical isomer D-Glu which is not transported by the systems of Glu uptake inhibited not only orthodromic and antidromic spikes, but also EPSC. Non-specific glutamate transporter inhibitor DL-threo-beta-hydroxyaspartic acid (THA, 400 microM) mimicked the effects of exogenous Glu and produced strong inhibition of both orthodromic and antidromic spikes, without any influence on the amplitude of EPSCs. Dihydrokainate (DHK, 300 microM), selective inhibitor of GLT-1 subtype of glutamate transporter, exerted a significant inhibitory action on the orthodromically evoked spikes and also on the EPSC. Our results indicate that extrasynaptic and PSD membranes of CA1 neurons form separate compartments differing in the mechanisms and efficiency of external Glu processing: the protection of PSD markedly prevails.

4-Aminopyridine↗

PubMed2004

Intracellular Na+ inhibits voltage-dependent N-type Ca2+ channels by a G protein betagamma subunit-dependent mechanism.

N-type voltage-dependent Ca(2+) channels (N-VDCCs) play important roles in neurotransmitter release and certain postsynaptic phenomena. These channels are modulated by a number of intracellular factors, notably by Gbetagamma subunits of G proteins, which inhibit N-VDCCs in a voltage-dependent (VD) manner. Here we show that an increase in intracellular Na(+) concentration inhibits N-VDCCs in hippocampal pyramidal neurones and in Xenopus oocytes. In acutely dissociated hippocampal neurones, Ba(2+) current via N-VDCCs was inhibited by Na(+) influx caused by the activation of NMDA receptor channels. In Xenopus oocytes expressing N-VDCCs, Ba(2+) currents were inhibited by Na(+) influx and enhanced by depletion of Na(+), after incubation in a Na(+)-free extracellular solution. The Na(+)-induced inhibition was accompanied by the development of VD facilitation, a hallmark of a Gbetagamma-dependent process. Na(+)-induced regulation of N-VDCCs is Gbetagamma dependent, as suggested by the blocking of Na(+) effects by Gbetagamma scavengers and by excess Gbetagamma, and may be mediated by the Na(+)-induced dissociation of Galphabetagamma heterotrimers. N-VDCCs may be novel effectors of Na(+)ion, regulated by the Na(+) concentration via Gbetagamma.

Animals↗

PubMed2003

The ASICs: signaling molecules? Modulators?

Acid-sensing ionic channels (ASICs) are almost ubiquitous in the mammalian nervous system, both at the periphery and in the brain. Strong evidence for the physiological function of these molecules has come from recent knockout experiments. Now it is clear that ASICs are important for certain sensory modalities (mechanoreception and nociception) at the periphery and for learning and memory in the brain. The actual mechanisms by which the acid-gated channels serve these functions remain unclear. The question of whether tissue pH is subject to quick fluctuations of a magnitude sufficient to activate ASICs is a crucial point that will determine the functional significance of these channels.

Acid Sensing Ion Channels↗