J. Zawilska, J. Zalewska-kaszubska, M. Przybysz
Feb 22, 2002
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Journal
Neuroscience Letters
Abstract
Abstract A selective (according to mammalian criteria) histamine (HA) H 2 -receptor radioligand [ 3 H]tiotidine ([ 3 H]TIOT) was used to characterize HA receptors in duck cerebral cortex by an in vitro binding technique. The specific binding of [ 3 H]TIOT to duck cerebral cortical membranes was found to be rapid, stable, saturable, reversible, and of high affinity. Saturation analysis resulted in a linear Scatchard plot suggesting binding to a single class of receptor binding sites with high affinity ( K d =19.5 nM) and high capacity ( B max =356 fmol/mg protein). Competition studies showed the following relative rank order of potency of various HA receptor ligands to inhibit the [ 3 H]TIOT binding: antagonists, tiotidine⪢ranitidine≈zolantidine≥cimetidine⪢mepyramine>thioperamide; agonists, HA≥4-methylHA>2-methylHA>dimaprit⪢ R α-methylHA. The biphasic nature of the displacement curve for HA and the effect of 5′-guanylimidodiphosphate indicate the coupling of the studied receptor to G-protein. It is suggested that HA receptors in the duck cerebral cortex labelled with [ 3 H]TIOT represent either avian-specific H 2 -like HA receptors or a novel subtype of HA receptors, coupled to a signalling pathway other than the adenylyl cyclase/cyclic adenosine monophosphate one.