Decavanadate modulates gating of TRPM4 cation channels.
We have tested the effects of decavanadate (DV), a compound known to interfere with ATP binding in ATP-dependent transport proteins, on TRPM4, a Ca(2+)-activated, voltage-dependent monovalent cation channel, whose activity is potently blocked by intracellular ATP(4-). Application of micromolar Ca(2+) concentrations to the cytoplasmic side of inside-out patches led to immediate current activation followed by rapid current decay, which can be explained by an at least 30-fold decreased apparent affinity for Ca(2+). Subsequent application of DV (10 microm) strongly affected the voltage-dependent gating of the channel, resulting in large sustained currents over the voltage range between -180 and +140 mV. The effect of DV was half-maximal at a concentration of 1.9 microm. The Ca(2+)- and voltage-dependent gating of the channel was well described by a sequential kinetic scheme in which Ca(2+) binding precedes voltage-dependent gating. The effects of DV could be explained by an action on the voltage-dependent closing step. Surprisingly, DV did not antagonize the effect of ATP(4-) on TRPM4, but caused a nearly 10-fold increase in the sensitivity of the ATP(4-) block. TRPM5, which is the most homologous channel to TRPM4, was not modulated by DV. The effect of DV was lost in a TRPM4 chimera in which the C-terminus was substituted with that of TRPM5. Deletion of a cluster in the C-terminus of TRPM4 containing positively charged amino acid residues with a high homology to part of the decavanadate binding site in SERCA pumps, completely abolished the DV effect but also accelerated desensitization. Deletion of a similar site in the N-terminus had no effects on DV responses. These results indicate that the C-terminus of TRPM4 is critically involved in mediating the DV effects. In conclusion, decavanadate modulates TRPM4, but not TRPM5, by inhibiting voltage-dependent closure of the channel.
Nilius
Bernd
B
Department of Physiology, Campus Gasthuisberg, KU Leuven, Herestraat 49, B-3000 Leuven, Belgium. bernd.nilius@med.kuleuven.ac.be
Prenen
Jean
J
Janssens
Annelies
A
Voets
Thomas
T
Droogmans
Guy
G
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015220:Calcium Channels / Q000502:physiology*; D027682:Cation Transport Proteins / Q000037:antagonists & inhibitors / Q000502:physiology*; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects* / Q000502:physiology; D008565:Membrane Proteins / Q000378:metabolism / Q000502:physiology; D051379:Mice; D050053:TRPM Cation Channels; D014638:Vanadates / Q000494:pharmacology*
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D027682:Cation Transport Proteins; D008565:Membrane Proteins; D050053:TRPM Cation Channels; C437888:TRPM4 protein, human; C404409:TRPM5 protein, human; C498617:Trpm5 protein, mouse; D014638:Vanadates; D000255:Adenosine Triphosphate