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Browsing by Subject "α-bungarotoxin"

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  • Salmelainen, Laura (2010)
    Neuronal nicotinic acetylcholine receptors are ligand-gated ion channel receptors that consist of five transmembral receptor subunits. They can form a functional receptor subtype solely out of alfa-subunits or out of a combination of alfa- and beta-subunits. The number of potential assembly of nicotinic receptor subunits is high because at least nine alfa-subunits (α2-α10) and three beta-subunits (β2-β4) have been recognized. The composition, location and pharmacological properties of different subtypes have not yet been fully characterized. However, it has been shown that the neuronal nicotinic receptors are involved in a wide range of physiological and pathofysiological processes especially in the central nervous system. Toxins from snakes and Conus -sea snails have proved to be important tools in neuropharmacological research, from which considerable information on structure and subunit combinations of the nicotinic receptors have been received. Receptors binding assays or autoradiographic experiments exploiting toxins have also been useful methods to locate the neuronal nicotinic receptors in mammalian brain. The aim of the experimental part of the Pro gradu was to characterize in vitro binding affinities of α-contoxin MII, α-conotoxin Vc1.1, neurotoxin II, α-cobratoxin and weak-toxin synthetized in Moscow and of well-known receptor ligands cytisine and methyllycaconitine to neuronal nicotinic receptors in SH-SY5Y- and SH-EP1-hα7-cell membrane preparations. SH-SY5Y-cells are known to express various neuronal receptor subtypes (α3* or α7) endogenously. For the SH-EP1-hα7-cells part, the cell line has been transfected with α7 nAChR-genes and it expresses only α7 receptor subtypes. Receptor competition studies were performed with [3H]-epibatidine (400 pM SH-SY5Y, 2000 pM SH-EP1-hα7) and the radioactivity was measured with a Microbeta- scintillation counter. [3H]-epibatidine was perceived to be displaced almost completely by cytisine and methyllycaconitine in both cell lines. In addition to this, the toxins were shown to bind to two distinct receptor-binding sites in SH-SY5Y-cells. Also α-contoxin MII and α-conotoxin Vc1.1 inhibited [3H]-epibatidine binding by biphasic manner, but the maximal displacement failed to be complete. From α-conotoxins only MII had affinity to α7 receptors in SH-EP1-hα7-cells. Neurotoxin II, α-cobratoxin and weak-toxin were not found to compete with [3H]-epibatidine for the same binding sites in SH-SY5Y-cells. The results confirm the assumption that cytisine and methyllycaconitine label various nAChR-subtypes. Instead, based on SH-SY5Y-cell assays α-conotoxins used in this study would seem to label spesifically only particular nAChR-subtypes. The receptor competition studies also confirm the prevalent conception that neurotoxin II, α-cobratoxin and weak-toxin do not bind to neuronal nicotinic receptor subtypes containing α3-subunits.