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[3H]5-hydroxytryptamine labels the agonist high affinity state of the cloned rat 5-HT4 receptor
N Adham1, C Gerald, L Schechter
1Synaptic Pharmaceutical Corporation, Paramus, NJ 07652, USA.
Abstract:
We have used the cloned rat 5-HT4 receptor, and determined that the single protein product produced is able to bind both [3H]5-HT and [3H]GR113808 ([1-[(2-methyl sulphonyl) amino] ethyl-4-piperidinyl] methyl-1-methyl-1H-indole-3-carboxylate) with high affinity. The affinities of agonists for the [3H]5-HT (agonist)-labelled receptor were significantly higher than for the [3H]GR113808 (antagonist)-labelled receptor. Furthermore, [3H]5-HT binding was reduced by addition of guanyl nucleotides. These results strongly support the hypothesis that the 5-HT4 receptor displays two interconvertible affinity states (high and low) for agonists, characteristic of many G protein coupled receptors. [3H]5-HT, at the concentration employed, therefore labels the agonist high affinity state of the 5-HT4 receptor in systems in which high densities of this receptor are found.
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