Novel mechanism of modulation at a ligand-gated ion channel; action of 5-Cl-indole at the 5-HT3A receptor.
The 5-HT3receptor is a prototypical member of the Cys-loop ligand-gated ion channel (LGIC) superfamily and an established therapeutic target. In addition to activation via the orthosteric site, receptor function can be modulated by allosteric ligands. We have investigated the pharmacological action of Cl-indole upon the 5-HT3A receptor and identified that this positive allosteric modulator possesses a novel mechanism of action for LGICs.



The impact of Cl-indole upon the 5-HT3receptor was assessed using single cell electrophysiological recordings and [3H]-granisetron binding in HEK293 cells stably expressing the 5-HT3receptor.



Cl-indole failed to evoke 5-HT3A receptor-mediated responses (up to 30 μM) or display affinity for the [3H]-granisetron binding site. However, in the presence of Cl-indole, termination of 5-HT application revealed tail currents mediated via the 5-HT3A receptor that were independent of the preceding 5-HT concentration but were antagonized by the 5-HT3receptor antagonist, ondansetron. These tail currents were absent in the 5-HT3AB receptor. Furthermore, the presence of 5-HT revealed a concentration-dependent increase in the affinity of Cl-indole for the orthosteric binding site of the human 5-HT3A receptor.



Cl-indole acts as both an orthosteric agonist and an allosteric modulator, but the presence of an orthosteric agonist (e.g. 5-HT) is a prerequisite to reveal both actions. Precedent for ago-allosteric action is available, yet the essential additional presence of an orthosteric agonist is now reported for the first time. This widening of the pharmacological mechanisms to modulate LGICs may offer further therapeutic opportunities.
Clinical and Experimental Medicine, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK.|School of Nursing Midwifery and Social Work, Birmingham City University, Edgbaston, UK.
Andrew D
AD
Powell
Clinical and Experimental Medicine, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK.
Gillian
G
Grafton
Clinical and Experimental Medicine, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK.
Alexander
A
Roberts
Clinical and Experimental Medicine, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK.
Shannon
S
Larkin
Clinical and Experimental Medicine, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK.
Nathanael
N
O'Neill
Clinical and Experimental Medicine, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK.
Josephine
J
Palandri
Department of Molecular and Cellular Neurobiology, VU University Amsterdam, Amsterdam, The Netherlands.
Reka
R
Otvos
Clinical and Experimental Medicine, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK.
Alison J
AJ
Cooper
Laboratory of Structural Neurobiology, KU Leuven, Leuven, Belgium.
Chris
C
Ulens
Clinical and Experimental Medicine, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK.|Department of Pharmacology and Therapeutics, School of Biomedical Sciences, Faculty of Medicine, Dentistry and Health Sciences, The University of Melbourne, Parkville, Victoria, Australia.
Nicholas M
NM
Barnes
D000494:Allosteric Regulation / Q000187:drug effects; D002478:Cells, Cultured; D057809:HEK293 Cells; D006801:Humans; D007211:Indoles / Q000494:pharmacology*; D058446:Ligand-Gated Ion Channels / Q000378:metabolism*; D008024:Ligands; D044406:Receptors, Serotonin, 5-HT3 / Q000378:metabolism*; D058827:Serotonin 5-HT3 Receptor Agonists / Q000494:pharmacology*
D007211:Indoles; D058446:Ligand-Gated Ion Channels; D008024:Ligands; D044406:Receptors, Serotonin, 5-HT3; D058827:Serotonin 5-HT3 Receptor Agonists
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