Ligand-gated ionic channels are integral membrane proteins that enable rapid and selective ion fluxes across biological membranes. In excitable cells, their role is crucial for generation and propagation of electrical signals. This survey describes recent results from studies performed in the Department of Cellular Neurophysiology, Institute of Physiology ASCR, aimed at exploring the conformational dynamics of the acetylcholine, glutamate and vanilloid receptors during their activation, inactivation and desensitization. Distinct families of ion channels were selected to illustrate a rich
complexity of the functional states and conformational transitions these proteins undergo. Particular attention is focused on structure-function studies and allosteric modulation of their activity. Comprehension of the fundamental principles of mechanisms involved in the operation of ligand-gated ion channels at the cellular and molecular level is an essential prerequisite for gaining an insight into the pathogenesis of many psychiatric and neurological disorders and for efficient development of novel specifically targeted drugs.
In this study we investigated whether also glycine fullfils the function as co-activator in glutamatergic activation of NMDA receptors in the neuronal apparatus of spontaneous motility in chick embryos.The successive application of glycine (5 or 10 mg/kg egg weight (e.w.) and glutamate (15 mg/kg e.w.) in a 10 min interval significantly increased the activation of spontaneous motility of 17-day-old chick embryos in comparison with the effect of glutamate alone. This effect did not depend on the order of application of the drugs. In 13-day-old embryos, glycine was ineffective in both doses. It is concluded from these results that the modulatory effect of glycine is evidently a later developmental acquisition (after day 15 of incubation) in the embryogenesis of NMDA-ergic activation of spontaneous motility in chick embryos similarly as glycinergic inhibition.
The early postdenervation depolarization of rat diaphragm muscle fibres (8-10 mV) is substantially smaller (3 mV) when muscle strips are bathed with 1 mM L-glutamate (GLÜ) or N-methyl-D-aspartate (NMDA). The effects of GLÜ and NMDA are not seen in the presence of aminophosphonovaleric acid (APV), a blocker of NMDA-subtype of glutamate receptors, 5 mM Mg2+ (which blocks NMDA-controlled ion channels) and L-nitroarginine methylester (NAME), an inhibitor of NO-synthase. This indicates that NMDA-subtype of GL(J receptors might be involved in the regulation of the membrane potential in muscle fibres, most probably through the NO-synthase system.
a1_The effect of lesions induced by bilateral intracerebroventricular (ICV) injection of quinolinate (250 nmol of QUIN/ventricle), a selective N-methyl-D-aspartate (NMDA) receptor agonist, on [3H]glutamate ([3H]Glu) binding to the main types of both ionotropic and metabotropic glutamate receptors (iGluR and mGluR) was investigated in synaptic membrane preparations from the hippocampi of 50-day-old rats. The membranes from QUIN injured brains revealed significantly lowered binding in iGluR (by 31 %) as well as in mGluR (by 22 %) as compared to the controls. Using selected glutamate receptor agonists as displacers of [3H]Glu binding we found that both the NMDA-subtype of iGluR and group I of mGluR are involved in this decrease of binding. Suppression of nitric oxide (NO) production by NG-nitro-L-arginine (50 nmol of NARG/ventricle) or the increase of NO generation by 3-morpholinylsydnoneimine (5 nmol of SIN-1/ventricle) failed to alter [3H]Glu or [3H]CPP (3-((D)-2-carboxypiperazin-4-yl)-[1,2-3H]-propyl-1-phosphonic acid; NMDA-antagonist) binding declines caused by QUIN-lesions. Thus, our findings indicate that both the NMDA-subtype of iGluR and group I of mGluR are susceptible to the QUIN-induced neurodegeneration in the rat hippocampus. However, the inhibition of NO synthesis did not reveal any protective action in the QUIN-evoked, NMDA-receptor mediated decrease of [3H]Glu binding., a2_Therefore, the additional mechanisms of QUIN action, different from direct NMDA receptor activation/NO production (e.g. lipid peroxidation induced by QUIN-Fe-complexes) cannot be excluded., V. Lisý, F. Šťastný., and Obsahuje bibliografii
Application of Cerebrolysin (0.1 /rg per 1 ml) by a fast microperfusion system induced an inward current of 0.2 to 1 nA in all neurones from newborn mouse hippocampi held at —30 mV membrane potential. Cerebrolysin- induced currents were reduced by the GABAa antagonist bicuculline (2 /¿M) by 65 %, by the NMDA antagonist aminophosphovaleric acid (APV, 10 /¿M) by 27 %, and by the non-NMDA antagonist cyanonitroquinoxalinedione (CNQX, 10 ¡utA) by 20 %. Cerebrolysin dialyzed through a 3.6 kD gut did not induce any transmembrane current but potentiated the response induced by GABA (10 /utA) to 135 %. We conclude that, in addition to amino acids which activate GABAa, NMDA and non-NMDA receptors, Cerebrolysin also contains a peptide which potentiates the GABAa receptor response.
NMDA receptors have received much attention over the last few decades, due to their role in many types of neural plasticity on the one hand, and their involvement in excitotoxicity on the other hand. There is great interest in developing clinically relevant NMDA receptor antagonists that would block excitotoxic NMDA receptor activation, without interfering with NMDA receptor function needed for normal synaptic transmission and plasticity. This review summarizes current understanding of the structure of NMDA receptors and the mechanisms of NMDA receptor activation and modulation, with special attention given to data describing the properties of various types of NMDA receptor inhibition. Our recent analyses point to certain neurosteroids as NMDA receptor inhibitors with desirable properties. Specifically, these compounds show use-dependent but voltage-independent block, that is predicted to preferentially target excessive tonic NMDA receptor activation. Importantly, neurosteroids are also characterized by use-independent unblock, compatible with minimal disruption of normal synaptic transmission. Thus, neurosteroids are a promising class of NMDA receptor modulators that may lead to the development of neuroprotective drugs with optimal therapeutic profiles., V. Vyklicky ... [et al.]., and Obsahuje bibliografii a bibliografické odkazy