TRPC5 is a Ca2+-activated channel functionally coupled to Ca2+-selective ion channels.
TRPC5 forms non-selective cation channels. Here we studied the role of internal Ca(2+) in the activation of murine TRPC5 heterologously expressed in human embryonic kidney cells. Cell dialysis with various Ca(2+) concentrations (Ca(2+)(i)) revealed a dose-dependent activation of TRPC5 channels by internal Ca(2+) with EC(50) of 635.1 and 358.2 nm at negative and positive membrane potentials, respectively. Stepwise increases of Ca(2+)(i) induced by photolysis of caged Ca(2+) showed that the Ca(2+) activation of TRPC5 channels follows a rapid exponential time course with a time constant of 8.6 +/- 0.2 ms at Ca(2+)(i) below 10 microM, suggesting that the action of internal Ca(2+) is a primary mechanism in the activation of TRPC5 channels. A second slow activation phase with a time to peak of 1.4 +/- 0.1 s was also observed at Ca(2+)(i) above 10 microM. In support of a Ca(2+)-activation mechanism, the thapsigargin-induced release of Ca(2+) from internal stores activated TRPC5 channels transiently, and the subsequent Ca(2+) entry produced a sustained TRPC5 activation, which in turn supported a long-lasting membrane depolarization. By co-expressing STIM1 plus ORAI1 or the alpha(1)C and beta(2) subunits of L-type Ca(2+) channels, we found that Ca(2+) entry through either calcium-release-activated-calcium or voltage-dependent Ca(2+) channels is sufficient for TRPC5 channel activation. The Ca(2+) entry activated TRPC5 channels under buffering of internal Ca(2+) with EGTA but not with BAPTA. Our data support the hypothesis that TRPC5 forms Ca(2+)-activated cation channels that are functionally coupled to Ca(2+)-selective ion channels through local Ca(2+) increases beneath the plasma membrane.
Gross
Stefan Alfred
SA
Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Universität des Saarlandes, 66421 Homburg/Saar, Germany.
Guzmán
Gustavo Adolfo
GA
Wissenbach
Ulrich
U
Philipp
Stephan Ernst
SE
Zhu
Michael Xi
MX
Bruns
Dieter
D
Cavalié
Adolfo
A
D000818:Animals; D002118:Calcium / Q000737:chemistry / Q000378:metabolism; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002614:Chelating Agents / Q000494:pharmacology; D006801:Humans; D007473:Ion Channels / Q000737:chemistry*; D007477:Ions; D008564:Membrane Potentials; D051379:Mice; D008954:Models, Biological; D050052:TRPC Cation Channels / Q000378:metabolism* / Q000502:physiology; D019284:Thapsigargin / Q000737:chemistry; D013997:Time Factors
D002614:Chelating Agents; D007473:Ion Channels; D007477:Ions; D050052:TRPC Cation Channels; C491780:TRPC5 protein, human; C112021:Trpc5 protein, mouse; D019284:Thapsigargin; D002118:Calcium