3 years ago

The muscarinic antagonists scopolamine and atropine are competitive antagonists at 5-HT3 receptors

The muscarinic antagonists scopolamine and atropine are competitive antagonists at 5-HT3 receptors
Scopolamine is a high affinity muscarinic antagonist that is used for the prevention of post-operative nausea and vomiting. 5-HT3 receptor antagonists are used for the same purpose and are structurally related to scopolamine. To examine whether 5-HT3 receptors are affected by scopolamine we examined the effects of this drug on the electrophysiological and ligand binding properties of 5-HT3A receptors expressed in Xenopus oocytes and HEK293 cells, respectively. 5-HT3 receptor-responses were reversibly inhibited by scopolamine with an IC 50 of 2.09 μM. Competitive antagonism was shown by Schild plot (pA 2 = 5.02) and by competition with the 5-HT3 receptor antagonists [3H]granisetron (K i = 6.76 μM) and G-FL (K i = 4.90 μM). The related molecule, atropine, similarly inhibited 5-HT evoked responses in oocytes with an IC 50 of 1.74 μM, and competed with G-FL with a K i of 7.94 μM. The reverse experiment revealed that granisetron also competitively bound to muscarinic receptors (K i = 6.5 μM). In behavioural studies scopolamine is used to block muscarinic receptors and induce a cognitive deficit, and centrally administered concentrations can exceed the IC 50 values found here. It is therefore possible that 5-HT3 receptors are also inhibited. Studies that utilise higher concentrations of scopolamine should be mindful of these potential off-target effects.

Publisher URL: www.sciencedirect.com/science

DOI: S0028390816301678

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