The Journal of General Physiology
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Published online 14 February 2006 doi:10.1085/jgp.200509409
The Rockefeller University Press, 0022-1295 $8.00
JGP, Volume 127, Number 3, 267-276
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ARTICLE

 Interaction of Acid-sensing Ion Channel (ASIC) 1 with the Tarantula Toxin Psalmotoxin 1 is State Dependent



Xuanmao Chen1, Hubert Kalbacher2, and Stefan Gründer1

1 Department of Physiology II, University of Würzburg, 97070 Würzburg, Germany
2 Interfakultäres Institut für Biochemie, University of Tübingen, 72074 Tübingen, Germany

Correspondence to Stefan Gründer: stefan.gruender{at}mail.uni-wuerzburg.de

Acid-sensing ion channels (ASICs) are Na+ channels gated by extracellular H+. Six ASIC subunits that are expressed in neurons have been characterized. The tarantula toxin psalmotoxin 1 has been reported to potently and specifically inhibit homomeric ASIC1a and has been useful to characterize ASICs in neurons. Recently we have shown that psalmotoxin 1 inhibits ASIC1a by increasing its apparent affinity for H+. However, the mechanism by which PcTx1 increases the apparent H+ affinity remained unclear. Here we show that PcTx1 also interacts with ASIC1b, a splice variant of ASIC1a. However, PcTx1 does not inhibit ASIC1b but promotes its opening; under slightly acidic conditions, PcTx1 behaves like an agonist for ASIC1b. Our results are most easily explained by binding of PcTx1 with different affinities to different states (closed, open, and desensitized) of the channel. For ASIC1b, PcTx1 binds most tightly to the open state, promoting opening, whereas for ASIC1a, it binds most tightly to the open and the desensitized state, promoting desensitization.

Abbreviations used in this paper: ASIC, acid-sensing ion channel; DHP, dihydropyridine; PcTx1, psalmotoxin 1.


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