Antiviral Drug Ivermectin at Nanomolar Concentrations Inhibits Glycine-Induced Chloride Current in Rat Hippocampal Neurons.

Ivermectin (IVM) belongs to the class of macrocyclic lactones, which is used as an antiparasitic agent. At present, the researchers focus on possibility to use IVM in treatment of certain forms of cancer and viral diseases such as COVID-19. The mechanisms of IVM action are not clear. It is assumed that IVM affects chloride channels and increases cytoplasmic concentration of chloride. This study examines the effect of IVM on chloride currents induced by glycine (IGly). Experiments were carried out on isolated pyramidal neurons of the rat hippocampus with whole-cell patch clamp. A short-term (600 msec) application of IVM in a concentration of 10 µM induced a slow inward current, which persisted after washing the neurons. The low concentrations (0.1-1000 nM) of IVM did not induce any novel current, but it rapidly and reversibly reduced the peak amplitude and accelerated desensitization of IGly in a dose-dependent manner. The threshold concentrations of IVM sufficient to reduce peak amplitude of IGly and to accelerate desensitization of IGly were 100 nM and 0.1 nM, respectively. The study revealed a high sensitivity of neuronal glycine receptors to IVM.

Copper Ions Reduce the Effect of Protons on Desensitization of Glycine Receptors.

Chloride current (IGly) evoked by the rapid (600 msec) application of glycine on isolated pyramidal neurons of the rat hippocampus was recorded using the patch clamp technique. We studied the effect of individual or combined application of copper ions (Cu2+) and protons (H+) on IGly. It was found that both Cu2+ (10 µM) and H+ (pH 7.0 and 6.0) applied separately caused a fast and reversible effect on IGly that included two components: a decrease in peak amplitude (Ipeak) and a decrease in the desensitization time constant (τdes). During combined application, the effects on Ipeak were additive, which indicates the independence of the mechanisms of these effects. At the same time, the effect of combined application of Cu2+ and H+ on τdes was not additive and sometimes a slowdown of the total desensitization was observed. The latter result suggests that H+ and Cu2+ can play the role of mutual antagonists when they affect the desensitization of GlyR.

The influence of acidic media on the effect of beta-amyloid peptide on the function of glycine receptor in hippocampal neurons.

We have previously shown that application of beta-amyloid peptide 1-42 (Aß) at picomolar/nanomolar concentrations caused a decrease in the peak amplitude and acceleration of desensitization of the glycine-activated chloride current (IGly) in hippocampal pyramidal neurons (Bukanova et al., 2016). The aim of this work was to study the effect of Aß on IGly in an acidified medium. The relevance of this work is determined by the fact that the pathogenic effects of Aß in Alzheimer's disease are usually accompanied by inflammatory processes and acidosis. The IGly was induced by 600 ms application of 100 µM (nearly EC50) or 500 µM (nearly saturating) glycine on isolated rat hippocampal neurons. The solution of glycine was neutral (pH 7.4) or acidic over a pH range of 5.0-7.0. It was found that 600 ms application of protons rapidly, reversibly and in dose-dependent manner decreased the peak amplitude and accelerated the desensitization of IGly. The effect of H+ on IGly desensitization did not depend on glycine concentration and may be considered noncompetitive, while the effect on IGly peak disappeared at saturating glycine concentration and can be regarded as a competitive. These characteristics of the proton effects on IGly coincide with the characteristics of the Aß effects on IGly. Experiments with joint application of Aß and H+ showed interdependence of their effects. Addition of Aß to perfusing solution reduced H+ effects on IGly while long pretreatment of Aß with acid solution prevented the effects of the peptide on IGly. Our results suggest the existence of common sites for Aß and H+ on the GlyR and indicate a mutual weakening of the inhibitory action of these molecules on IGly.

Functional modulation of strychnine-sensitive glycine receptors in rat hippocampal pyramidal neurons by amyloid-ß protein (1-42).

Amyloid-ß peptide (Aß) is considered a key protein in the pathogenesis of Alzheimer's disease because of its neurotoxicity, resulting in impaired synaptic function and memory. On the other hand, it was demonstrated that low (picomolar) concentrations of Aß enhance synaptic plasticity and memory, suggesting that in the healthy brain, physiological Aß concentrations are necessary for normal cognitive functions. In the present study, we found that Aß (1-42) in concentrations of 10 pМ - 100nМ enhanced desensitization of the glycine-activated current in isolated CA3 pyramidal neurons and also reversibly suppressed its peak amplitude during short (600ms) co-application with agonist. The effect was most prominent at low glycine concentrations. When glycine receptors were activated by other receptor agonists - taurine and ß-alanine, the changes of current kinetics and amplitudes induced by Aß had a similar character. When Aß (100 pM) was added to the bath solution, it caused, besides acceleration of desensitization, more pronounced reduction of peak current amplitude. This effect developed slowly, during a few minutes, and was more prominent at saturating concentrations of agonists. The results suggest that Aß interacts with glycine receptors through three different mechanisms - by enhancing receptor desensitization, by rapid inhibition of the receptor, and also by means of a slowly developing inhibition of the amplitude of the current, possibly through intracellular mechanisms. The observed changes in the activity of glycine receptors induced by Aß can lead to suppression of the tonic inhibition of hippocampal neurons mediated by extrasynaptic glycine receptors.

Lithium ions in nanomolar concentration modulate glycine-activated chloride current in rat hippocampal neurons.

Lithium salts are successfully used to treat bipolar disorder. At the same time, according to recent data lithium may be considered as a candidate medication for the treatment of neurodegenerative disorders. The mechanisms of therapeutic action of lithium have not been fully elucidated. In particular, in the literature there are no data on the effect of lithium on the glycine receptors. In the present study we investigated the effect of Li(+) on glycine-activated chloride current (IGly) in rat isolated pyramidal hippocampal neurons using patch-clamp technique. The effects of Li(+) were studied with two glycine concentrations: 100 µM (EC50) and 500 µM (nearly saturating). Li(+) was applied to the cell in two ways: first, by 600 ms co-application with glycine through micropipette (short application), and, second, by addition to an extracellular perfusate for 10 min (longer application). Li(+) was used in the range of concentrations of 1 nM-1 mM. Short application of Li(+) caused two effects: (1) an acceleration of desensitization (a decrease in the time of half-decay, or "τ") of IGly induced by both 100 µM and 500 µM glycine, and (2) a reduction of the peak amplitude of the IGly, induced by 100 µM, but not by 500 µM glycine. Both effects were not voltage-dependent. Dose-response curves for both effects were N-shaped with two maximums at 100 nM and 1 mM of Li(+) and a minimum at 1 µM of Li(+). This complex form of dose-response may indicate that the process activated by high concentrations of lithium inhibits the process that is sensitive to low concentrations of lithium. Longer application of Li(+)caused similar effects, but in this case 1 µM lithium was effective and the dose-effect curves were not N-shaped. The inhibitory effect of lithium ions on glycine-activated current suggests that lithium in low concentrations is able to modulate tonic inhibition in the hippocampus. This important property of lithium should be considered when using this drug as a therapeutic agent.

Fe(2+) and Fe(3+) in micromolar concentrations modulate glycine-induced Cl(-) current in rat hippocampal neurons.

The effects of Fe(2+) and Fe(3+) on glycine-activated chloride current (IGly) were studied in rat isolated pyramidal hippocampal neurons using patch-clamp technique in whole-cell configuration. 25, 100 or 500 µM glycine was applied for 600 ms with 40s intervals. Fe(2+) and Fe(3+) were co-applied with glycine in the range of concentrations of 0.01-100 µM. We found that Fe(2+) and Fe(3+) affected IGly in a similar manner. Two types of effects of iron on IGly were observed. In low concentrations (0.1 µM) Fe ions caused an acceleration of the IGly desensitization, and the effect was more pronounced for IGly induced by 100 and 500 µM glycine than by 25 µM glycine. Higher Fe concentrations (1-100 µM) decreased the peak amplitude of IGly with weak influence on its kinetics. The values of IC50 of the effect were close to 10 µM for all glycine concentrations tested. The effect of iron on IGly peak did not depend on the membrane potential. This inhibition was noncompetitive and voltage-independent, suggesting that Fe ions do not exert their action on the agonist binding site of GlyRs or block the channel pore. An important characteristic of both effects of Fe was their progressive development during repetitive Fe applications (use-dependence). Our results suggest an existence of at least two binding sites for Fe ions which vary in affinity and mechanism of action, with the low-affinity site suppressing the activity of the high-affinity one. Physiological implication of our observations is that Fe ions in low micromolar concentrations can suppress tonic inhibition and cause hyperexcitability in hippocampus.

Amyloid ß peptide (25-35) in picomolar concentrations modulates the function of glycine receptors in rat hippocampal pyramidal neurons through interaction with extracellular site(s).

ß-Amyloid peptide (Aß) plays a central role in the pathogenesis of Alzheimer׳s disease, but in lower amounts it is found in normal brains where it participates in physiological processes and probably regulates synaptic plasticity. This study investigated the effects of physiologically relevant concentrations of Aß (1 pM-100 nM), fragment 25-35, on glycine-mediated membrane current in acutely isolated rat hippocampal pyramidal neurons using whole-cell patch-clamp technique. We have found that short (600 ms) co-application of glycine with Aß caused reversible dose-dependent and voltage-independent acceleration of desensitization of glycine current. The peak amplitude of the current remained unchanged. The effect of picomolar Aß concentrations persisted in the presence of 1 µM Aß in the pipette solution, implying that Aß bounds to extracellular site(s). Concentration-dependence curve was N-shaped with maximums at 100 pM and 100 nM, suggesting the existence of two binding sites, which may interact with each other. Glycine current resistant to 100 µM picrotoxin, was insensitive to Aß, which suggests that Aß affected mainly homomeric glycine receptors. When Aß was added to bath solution, besides acceleration of desensitization, it caused reversible dose-dependent reduction of glycine current peak amplitude. These results demonstrate that physiological (picomolar) concentrations of Aß reversibly augment the desensitization of glycine current, probably by binding to external sites on homomeric glycine receptors. Furthermore, Aß can suppress the peak amplitude of glycine current, but this effect develops slowly and may be mediated through some intracellular machinery.

Impact of amyloid-ß peptide (1-42) on voltage-gated ion currents in molluscan neurons.

Different types of voltage-gated ion currents were recorded in isolated neurons of snail Helix pomatia using the two-microelectrode voltage-clamp technique. Application of amyloid-ß peptide (1-42, 1-10 µM) in the bathing solution did not change delayed rectifier K(+)-current and leakage current, but enhanced inactivation of Ca(2+)-current and blocked Ca(2+)-dependent K(+)-current.

The nootropic drug vinpocetine modulates different types of potassium currents in molluscan neurons.

Three types of high-threshold K+ currents were recorded in isolated neurons of the snail Helix pomatia using a two-microelectrode voltage clamp technique: transient K+ current (I(A)), delayed rectifier (I(KD)) and Ca2+-dependent K+ current (I(K(Ca))). Vinpocetine (1-100 microM) applied to the bath affected different types of K+ current in different ways: I(A) was increased (35+/-14%), I(KD) was moderately inhibited (20+/-9%) and I(K(Ca)) was strongly suppressed (45+/-15%). When I(A) and I(K(Ca)) were present in the same cell, vinpocetine exerted a dual effect on the total K+ current, depending on the amplitude of the test stimulus. In the presence of vinpocetine, the I-V curve crossed the control I-V curve. The inhibition of I(K(Ca)) by vinpocetine between 1 and 100 microM is unlikely to be a result of Ca2+ current (I(Ca)) suppression, as the latter was inhibited only at vinpocetine concentrations exceeding 300 microM. Dibutyryl cyclic GMP (dbcGMP) (but not dbcAMP) mimicked the effects of vinpocetine in the majority of cells tested (coefficient of correlation r=0.60, P<0.05, n=22). The data suggest that modulation of different types of K+ current in neuronal membrane can contribute, at least partially, to the nootropic effect of vinpocetine through the regulation of intracellular Ca2+ concentration.

Enhancement of low-threshold A-current of the neuronal membrane by vinpocetine.

A low-threshold fast inactivating K+ current (I(Alth)) was recorded in isolated land snail neurons using the two-microelectrode voltage clamp method. A nootropic drug, vinpocetine, applied to the extracellular medium at a concentration of 1-100 microM potentiated I(Alth). The potentiation consisted in a rise of its peak amplitude and an increase of the half-decay time. Vinpocetine did not cause a shift of the steady-state activation and inactivation curves along the potential axis. Dibutyryl cyclic GMP (dcGMP) also increased the peak amplitude but did not change the time of current half-decay. dcAMP did not potentiate I(Alth). The possible role of K+-current potentiation in neuronal membranes in therapy of dementia is discussed.

The effects of piracetam and its novel peptide analogue GVS-111 on neuronal voltage-gated calcium and potassium channels.

1. With the use of the two-microelectrode voltage-clamp method, three types of voltage-activated ionic currents were examined in isolated neurons of the snail Helix pomatia: high-threshold Ca2+ current (ICa), high-threshold Ca(2+)-dependent K+ current (IK(Ca)) and high-threshold K+ current independent of Ca2+ (IK(V)). 2. The effect of bath application of the nootropics piracetam and a novel piracetam peptide analog, ethyl ester of N-phenyl-acetyl-L-prolyl-glycine (GVS-111), on these three types of voltage-activated ionic currents was studied. 3. In more than half of the tested cells, ICa was resistant to both piracetam and GVS-111. In the rest of the cells, ICa decreased 19 +/- 7% with 2 mM of piracetam and 39 +/- 14% with 2 microM of GVS-111. 4. IK(V) in almost all cells tested was resistant to piracetam at concentrations up to 2 mM. However, IK(V) in two-thirds of the cells was sensitive to GVS-111, being suppressed 49 +/- 18% with 1 microM GVS-111. 5. IK(Ca) appeared to be the most sensitive current of those studied to both piracetam and GVS-111. Piracetam at 1 mM and GVS-111 at 0.1 microM decreased the amplitude of IK(Ca) in most of the cells examined by 49 +/- 19% and 69 +/- 24%, respectively. 6. The results suggest that piracetam and GVS-111 suppression of voltage-activated calcium and potassium currents of the neuronal membrane may regulate (both up and down) Ca2+ influx into neurons.