Voltage-dependent changes of TRPV6-mediated Ca2+ currents.
The physiological role and activation mechanism for most proteins of the transient receptor potential (TRP) family are unknown. This is also the case for the highly Ca(2+) selective transient receptor potential vanilloid type 6 (TRPV6) channel. Patch clamp experiments were performed on transiently transfected human embryonic kidney (HEK) cells to address this issue. Currents were recorded under various conditions of intracellular Ca(2+) buffering and monitored at the same voltage throughout. No TRPV6-mediated Ca(2+) entry was detected under in vivo Ca(2+) buffering conditions at a slightly negative holding potential; however, moderate depolarization resulted in current activation. Very similar results were obtained with different Ca(2+) chelators, either EGTA or BAPTA dialyzing the cell. TRPV6 channel activity showed a negative correlation with the intracellular free Ca(2+) concentration ([Ca(2+)](i)) and was modulated by the membrane potential: Hyperpolarization decreases and depolarization increases TRPV6-mediated currents. Monovalent ions permeated TRPV6 channels in the absence of extracellular divalent cations. These currents were resistant to changes in the holding potential while the negative correlation to the [Ca(2+)](i) was conserved, indicating that the voltage-dependent current changes depend on blocking and unblocking the charge carrier Ca(2+) within the pore. In summary, these results suggest that the voltage dependence of TRPV6-mediated Ca(2+) influx is of physiological importance since it occurs at cytosolic Ca(2+) buffering and takes place within a physiologically relevant membrane potential range.
Bödding
Matthias
M
Experimentelle und Klinische Pharmakologie und Toxikologie, Universität des Saarlandes, D-66421 Homburg, Germany. matthias.boedding@uniklinik-saarland.de
D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology*; D002460:Cell Line; D004533:Egtazic Acid / Q000494:pharmacology; D004594:Electrophysiology; D006801:Humans; D008564:Membrane Potentials / Q000502:physiology*; D018408:Patch-Clamp Techniques; D050916:TRPV Cation Channels; D014162:Transfection
D015220:Calcium Channels; D050916:TRPV Cation Channels; C120776:TRPV6 channel; D004533:Egtazic Acid; D002118:Calcium