Block of TRPC5 channels by 2-aminoethoxydiphenyl borate: a differential, extracellular and voltage-dependent effect

Authors


School of Biomedical Sciences, University of Leeds, Leeds LS2 9JT. E-mail: d.j.beech@leeds.ac.uk

Abstract

  • 12-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.
  • 2Using 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.
  • 3The concentration–response curve has an IC50 of 20 μM 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.
  • 4In whole-cell and excised membrane patch recordings, 2-APB acts from the extracellular but not intracellular face of the membrane.
  • 5Block of TRPC5 by 2-APB is less at positive voltages, suggesting that it enters the electric field or acts by modulating channel gating.
  • 62-APB also blocks TRPC6 and TRPM3 expressed in HEK-293 cells, but not TRPM2.
  • 7Block 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.
  • 8Our 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.

British Journal of Pharmacology (2005) 145, 405–414. doi:10.1038/sj.bjp.0706197

Ancillary