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 μ m ) 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 μ m . 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.