Mg2+-dependent gating and strong inward rectification of the cation channel TRPV6.
TRPV6 (CaT1/ECaC2), a highly Ca(2+)-selective member of the TRP superfamily of cation channels, becomes permeable to monovalent cations in the absence of extracellular divalent cations. The monovalent currents display characteristic voltage-dependent gating and almost absolute inward rectification. Here, we show that these two features are dependent on the voltage-dependent block/unblock of the channel by intracellular Mg(2+). Mg(2+) blocks the channel by binding to a site within the transmembrane electrical field where it interacts with permeant cations. The block is relieved at positive potentials, indicating that under these conditions Mg(2+) is able to permeate the selectivity filter of the channel. Although sizeable outward monovalent currents were recorded in the absence of intracellular Mg(2+), outward conductance is still approximately 10 times lower than inward conductance under symmetric, divalent-free ionic conditions. This Mg(2+)-independent rectification was preserved in inside-out patches and not altered by high intracellular concentrations of spermine, indicating that TRPV6 displays intrinsic rectification. Neutralization of a single aspartate residue within the putative pore loop abolished the Mg(2+) sensitivity of the channel, yielding voltage-independent, moderately inwardly rectifying monovalent currents in the presence of intracellular Mg(2+). The effects of intracellular Mg(2+) on TRPV6 are partially reminiscent of the gating mechanism of inwardly rectifying K(+) channels and may represent a novel regulatory mechanism for TRPV6 function in vivo.
Voets
Thomas
T
Department of Physiology, Campus Gasthuisberg, KU Leuven, Belgium. thomas.voets@med.kuleuven.ac.be
Janssens
Annelies
A
Prenen
Jean
J
Droogmans
Guy
G
Nilius
Bernd
B
D001224:Aspartic Acid; D002121:Calcium Channel Blockers / Q000378:metabolism / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D002412:Cations / Q000494:pharmacology; D002460:Cell Line; D004347:Drug Interactions; D004594:Electrophysiology; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism; D015640:Ion Channel Gating; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism / Q000494:pharmacology*; D010539:Permeability; D017434:Protein Structure, Tertiary / Q000235:genetics; D050916:TRPV Cation Channels
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D002412:Cations; D050916:TRPV Cation Channels; C120776:TRPV6 channel; D001224:Aspartic Acid; D008274:Magnesium