Block of TRPC5 channels by 2-aminoethoxydiphenyl borate: a differential, extracellular and voltage-dependent effect.
1 2-aminoethoxydiphenyl borate (2-APB) has been widely used to examine the roles of inositol 1,4,5-trisphosphate receptors (IP3Rs) and store-operated Ca2+ entry and is an emerging modulator of cationic channels encoded by transient receptor potential (TRP) genes. 2 Using Ca2+-indicator dye and patch-clamp recording we first examined the blocking effect of 2-APB on human TRPC5 channels expressed in HEK-293 cells. 3 The concentration-response curve has an IC50 of 20 microM and slope close to 1.0, suggesting one 2-APB molecule binds per channel. The blocking effect is not shared by other Ca2+ channel blockers including methoxyverapamil, nifedipine, N-propargylnitrendipine, or berberine. 4 In whole-cell and excised membrane patch recordings, 2-APB acts from the extracellular but not intracellular face of the membrane. 5 Block of TRPC5 by 2-APB is less at positive voltages, suggesting that it enters the electric field or acts by modulating channel gating. 6 2-APB also blocks TRPC6 and TRPM3 expressed in HEK-293 cells, but not TRPM2. 7 Block of TRP channels by 2-APB may be relevant to cell proliferation because 2-APB has a greater inhibitory effect on proliferation in cells overexpressing TRPC5. 8 Our data indicate a specific and functionally important binding site on TRPC5 that enables block by 2-APB. The site is only available via an extracellular route and the block shows mild voltage-dependence.
Xu
Shang-Zhong
SZ
School of Biomedical Sciences, University of Leeds, Leeds LS2 9JT.
Zeng
Fanning
F
Boulay
Guylain
G
Grimm
Christian
C
Harteneck
Christian
C
Beech
David J
DJ
D000818:Animals; D001599:Berberine / Q000494:pharmacology; D001896:Boron Compounds / Q000494:pharmacology*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015220:Calcium Channels / Q000235:genetics / Q000502:physiology*; D027682:Cation Transport Proteins / Q000235:genetics / Q000502:physiology*; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D005711:Gallopamil / Q000494:pharmacology; D006801:Humans; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D009543:Nifedipine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D050052:TRPC Cation Channels; D000074287:TRPC6 Cation Channel; D050053:TRPM Cation Channels; D013997:Time Factors; D014162:Transfection
D001896:Boron Compounds; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D027682:Cation Transport Proteins; D050052:TRPC Cation Channels; C491780:TRPC5 protein, human; D000074287:TRPC6 Cation Channel; D050053:TRPM Cation Channels; C475667:TRPM3 protein, human; C492146:Trpc6 protein, mouse; D001599:Berberine; D005711:Gallopamil; C109986:2-aminoethoxydiphenyl borate; D009543:Nifedipine