Interaction of acid-sensing ion channel (ASIC) 1 with the tarantula toxin psalmotoxin 1 is state dependent.
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.
Chen
Xuanmao
X
Department of Physiology II, University of Würzburg, 97070 Würzburg, Germany.
Kalbacher
Hubert
H
Gründer
Stefan
S
D062565:Acid Sensing Ion Channels; D000818:Animals; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D006863:Hydrogen-Ion Concentration; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D008565:Membrane Proteins / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000502:physiology*; D009419:Nerve Tissue Proteins / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000502:physiology*; D009865:Oocytes / Q000737:chemistry / Q000187:drug effects / Q000502:physiology*; D010455:Peptides; D011485:Protein Binding; D051381:Rats; D012964:Sodium / Q000378:metabolism*; D015222:Sodium Channels / Q000737:chemistry / Q000502:physiology*; D013111:Spider Venoms / Q000008:administration & dosage* / Q000737:chemistry; D014982:Xenopus laevis
D062565:Acid Sensing Ion Channels; C568268:Asic1 protein, rat; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; C413209:PcTX1 protein, Psalmopoeus cambridgei; D010455:Peptides; D015222:Sodium Channels; D013111:Spider Venoms; D012964:Sodium