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Identification of the Ca2+ blocking site of acid-sensing ion channel (ASIC) 1: implications for channel gating.
- Source :
-
The Journal of general physiology [J Gen Physiol] 2004 Oct; Vol. 124 (4), pp. 383-94. - Publication Year :
- 2004
-
Abstract
- Acid-sensing ion channels ASIC1a and ASIC1b are ligand-gated ion channels that are activated by H+ in the physiological range of pH. The apparent affinity for H+ of ASIC1a and 1b is modulated by extracellular Ca2+ through a competition between Ca2+ and H+. Here we show that, in addition to modulating the apparent H+ affinity, Ca2+ blocks ASIC1a in the open state (IC50 approximately 3.9 mM at pH 5.5), whereas ASIC1b is blocked with reduced affinity (IC50 > 10 mM at pH 4.7). Moreover, we report the identification of the site that mediates this open channel block by Ca2+. ASICs have two transmembrane domains. The second transmembrane domain M2 has been shown to form the ion pore of the related epithelial Na+ channel. Conserved topology and high homology in M2 suggests that M2 forms the ion pore also of ASICs. Combined substitution of an aspartate and a glutamate residue at the beginning of M2 completely abolished block by Ca2+ of ASIC1a, showing that these two amino acids (E425 and D432) are crucial for Ca2+ block. It has previously been suggested that relief of Ca2+ block opens ASIC3 channels. However, substitutions of E425 or D432 individually or in combination did not open channels constitutively and did not abolish gating by H+ and modulation of H+ affinity by Ca2+. These results show that channel block by Ca2+ and H+ gating are not intrinsically linked.
- Subjects :
- Acid Sensing Ion Channels
Amino Acid Substitution
Animals
Binding Sites
Cells, Cultured
Mutagenesis, Site-Directed
Oocytes physiology
Rats
Recombinant Proteins chemistry
Recombinant Proteins metabolism
Structure-Activity Relationship
Xenopus laevis
Calcium chemistry
Calcium metabolism
Ion Channel Gating physiology
Membrane Potentials physiology
Membrane Proteins chemistry
Membrane Proteins physiology
Nerve Tissue Proteins chemistry
Nerve Tissue Proteins physiology
Sodium Channels chemistry
Sodium Channels physiology
Subjects
Details
- Language :
- English
- ISSN :
- 0022-1295
- Volume :
- 124
- Issue :
- 4
- Database :
- MEDLINE
- Journal :
- The Journal of general physiology
- Publication Type :
- Academic Journal
- Accession number :
- 15452199
- Full Text :
- https://doi.org/10.1085/jgp.200308973