Antagonism by selected classical irreversible competitive antagonists : an investigation into the proposed non-specific mechanisms involved / Johannes Bodenstein

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dc.contributor.author Bodenstein, Johannes
dc.date.accessioned 2008-11-27T08:58:06Z
dc.date.available 2008-11-27T08:58:06Z
dc.date.issued 2003
dc.identifier.uri http://hdl.handle.net/10394/92
dc.description Thesis (Ph.D. (Pharmacology))--North-West University, Potchefstroom Campus, 2004.
dc.description.abstract Many irreversible antagonists are known to bind irreversibly to pharmacological receptors. However, few studies suggest that these irreversible antagonists may also display irreversible non-specific antagonism by binding irreversibly to non-syntopic binding sites on the receptor macromolecule, whereby they modulate the signal transduction of these receptors or reduce the agonist binding affmity. The aim of this study was to investigate whether the classical irreversible antagonists phenoxybenzamine, benextramine and 4-DAMP mustard display irreversible nonspecific antagonism at various G protein-coupled receptor (GPCR) types. In addition, the subcellular mechanism whereby benextramine displays irreversible non-specific antagonism was investigated. Three cell lines were employed to investigate the antagonism by these irreversible antagonists: Chinese hamster ovary (CHO-K1) cells transfected to express the porcine a2A-adrenoceptor (a2A-AR) at higher (a2A-H) or lower (a2A-L) numbers, human neuroblastoma (SH-SY5Y) cells that endogenously express muscarinic acetylcholine receptors (mACh-Rs), and SH-SY5Y cells transfected (5HT2A-SH-SY5Y)o express the human 5HT2A-serotonirne ceptor (5HTZA-R).C ells of the appropriate cell line were pre-treated at the appropriate concentrations and incubation times with an appropriate irreversible antagonist, with or without an appropriate reversible competitive antagonist at a sufficient concentration to protect the specific receptors. This was followed by washing procedures with drug-free media to rinse any unbound or reversibly bound drugs from the cells. When appropriate, cell membranes were prepared. Receptor function was evaluated by measuring whole-cell [3H]-cAMP or [3H]-IPx acumulation, or the binding of [35S]-GTPyS to membraness. Receptor concentrations were determined from radioligand-binding assays. In addition, the constitutive [35S]-GTPyS binding to Go protein before and after pre-treatment with benextramine was investigated. Results suggest that phenoxybenzamine (100 uM, 20 minutes) and benextramine (10 uM, 20 minutes) display irreversible non-specific antagonism at a2A-ARs when measuring Gi-mediated effects in a2A-L cells, but the affinity for a2A-ARs in a2A-H cells was not changed. In addition, it was found that the observed irreversible nonspecific antagonism by benextramine appears to be time- and concentration-dependent. When the mechanism of irreversible antagonism by benextramine was further investigated, benextramine reduced the binding of [35S]-GTPyS to a2A-H membranes with protected a2A-ARs, but did not modulate the constitutive binding of [35S]-GTPyS to Go. In addition, benextramine displays irreversible non-specific antagonism by inhibiting the G,-mediated effects of a2A-ARs in a2A-H cells and the Gq-mediated effects of mACh-Rs or 5HT2A-Rs in SH-SY5Y or 5HT2A-SH-SY5Y cells respectively. 4-DAMP mustard (100 uM, 20 minutes) did not display irreversible non-specific antagonism at mACh-Rs in SH-SY5Y cells, but irreversible non-specific antagonism was observed when the incubation time was increased (100 uM, 60 minutes). In conclusion it was found that phenoxybenzamine, benextramine and 4-DAMP mustard display irreversible non-specific antagonism at typical experimental conditions. These findings confirm concerns in literature and supports the possibility that more irreversible antagonists could display irreversible non-specific antagonism, and that could influence the interpretation of data obtained with such drugs. In addition, benextramine may prove to be a useful experimental drug in studying GPCR signalling.
dc.publisher North-West University
dc.subject 5HT[2A]-serotonin receptor en
dc.subject 4-DAMP mustard en
dc.subject Alpha[2A]-adrenoceptor en
dc.subject Benextramine en
dc.subject G protein-coupled receptor en
dc.subject Irreversible antagonist en
dc.subject Muscarinic acetylcholine receptor en
dc.subject Non-syntopic binding site en
dc.subject Phenoxybenzamine en
dc.subject Specific receptor en
dc.subject 4-DAMP mosterd en
dc.subject 5HT[2A]-serotonienreseptor en
dc.subject Alpha[2A]-adrenoseptor en
dc.subject Benekstramien en
dc.subject Fenoksibensamien en
dc.subject G-proteïengekoppelde reseptor en
dc.subject Muskariniese asetielcholienreseptor en
dc.subject Non-sintopiese bindingsetel en
dc.subject Onomkeerbare antagonis en
dc.title Antagonism by selected classical irreversible competitive antagonists : an investigation into the proposed non-specific mechanisms involved / Johannes Bodenstein en
dc.title.alternative Antagonisme deur geselekteerde klassieke onomkeerbare kompeterende antagoniste : 'n ondersoek na die voorgestelde non-spesifieke meganismes betrokke
dc.title.alternative Irreversible non-specific antagonism
dc.type Thesis en
dc.description.thesistype Doctoral

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