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This Article Full Text Full Text (PDF) Supplemental Data All Versions of this Article: 586/15/3629    most recent jphysiol.2008.153486v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Noam, Y. Articles by van Hooft, J. A. PubMed PubMed Citation Articles by Noam, Y. Articles by van Hooft, J. A. Related Collections Neuroscience

¹ Swammerdam Institute for Life Sciences, Center for NeuroScience, University of Amsterdam, the Netherlands

Natively expressed serotonin 5-HT₃ receptors typically possess a negative-slope conductance region in their I–V curve, due to a voltage-dependent block by external Ca²⁺ ions. However, in almost all studies performed with heterologously expressed 5-HT₃ receptors, this feature was not observed. Here we show that mere addition of ATP to the pipette solution is sufficient to reliably observe a voltage-dependent block in homomeric (h5-HT_3A) and heteromeric (h5-HT_3AB) receptors expressed in HEK293 cells. A similar block was observed with a plethora of molecules containing a phosphate moiety, thus excluding a role of phosphorylation. A substitution of three arginines in the intracellular vestibule of 5-HT_3A with their counterpart residues from the 5-HT_3B subunit (RRR-QDA) was previously shown to dramatically increase single channel conductance. We find this mutant to have a linear I–V curve that is unaffected by the presence of ATP, with a fractional Ca²⁺ current (Pf%) that is reduced (1.8 ± 0.2%) compared to that of the homomeric receptor (4.1 ± 0.2%), and similar to that of the heteromeric form (2.0 ± 0.3%). Moreover, whereas ATP decreased the Pf% of the homomeric receptor, this was not observed with the RRR-QDA mutant. Finally, ATP was found to be critical for voltage-dependent channel block also in hippocampal interneurons that natively express 5-HT₃ receptors. Taken together, our results indicate a novel mechanism by which ATP, and similar molecules, modulate 5-HT₃ receptors via interactions with the intracellular vestibule of the receptor.

(Received 4 March 2008; accepted after revision 12 June 2008; first published online 12 June 2008)
Corresponding author J.A. van Hooft: Swammerdam Institute for Life Sciences, Center for NeuroScience, University of Amsterdam, PO Box 94084, NL-1090 GB Amsterdam, the Netherlands. Email:  j.a.vanhooft{at}uva.nl