Agonist-induced changes in Ca(2+) permeation through the nociceptor cation channel TRPA1.
The Ca(2+)-permeable cation channel TRPA1 acts as an ionotropic receptor for various pungent compounds and as a noxious cold sensor in sensory neurons. It is unclear what proportion of the TRPA1-mediated current is carried by Ca(2+) ions and how the permeation pathway changes during stimulation. Here, based on the relative permeability of the nonstimulated channel to cations of different size, we estimated a pore diameter of approximately 11 A. Combined patch-clamp and Fura-2 fluorescence recordings revealed that with 2 mM extracellular Ca(2+), and at a membrane potential of -80 mV, approximately 17% of the inward TRPA1 current is carried by Ca(2+). Stimulation with mustard oil evoked an apparent dilatation of the pore of 3 A and an increase in divalent cation selectivity and fractional Ca(2+) current. Mutations in the putative pore that reduced the divalent permeability and fractional Ca(2+) current also prevented mustard-oil-induced increases in Ca(2+) permeation. It is interesting that fractional Ca(2+) currents for wild-type and mutant TRPA1 were consistently higher than values predicted based on biionic reversal potentials using the Goldman-Hodgkin-Katz equation, suggesting that binding of Ca(2+) in the pore hinders monovalent cation permeation. We conclude that the pore of TRPA1 is dynamic and supports a surprisingly large Ca(2+) influx.
Karashima
Yuji
Y
Department of Molecular Cell Biology, Katholieke Universiteit Leuven, Belgium.
Prenen
Jean
J
Talavera
Karel
K
Janssens
Annelies
A
Voets
Thomas
T
Nilius
Bernd
B
D000818:Animals; D016466:CHO Cells; D002118:Calcium / Q000378:metabolism*; D002413:Cations, Divalent / Q000378:metabolism; D002414:Cations, Monovalent / Q000378:metabolism; D002463:Cell Membrane Permeability; D006224:Cricetinae; D003412:Cricetulus; D015640:Ion Channel Gating; D051379:Mice; D009619:Nociceptors / Q000378:metabolism*; D016062:Porosity; D011726:Pyridinium Compounds / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D000074025:TRPA1 Cation Channel; D050051:Transient Receptor Potential Channels / Q000819:agonists* / Q000378:metabolism*
D002413:Cations, Divalent; D002414:Cations, Monovalent; C073804:FM1 43; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds; D000074025:TRPA1 Cation Channel; D050051:Transient Receptor Potential Channels; C475685:Trpa1 protein, mouse; D002118:Calcium