Abstract
TRPM4b (in contrast to the short splice variant TRPM4a) is a Ca2+-activated but Ca2+-impermeable cation channel. We have studied TRPM4 currents in inside-out patches. Supramicromolar Ca2+ concentrations applied at the inner side, [Ca2+]i, activated TRPM4 with an EC50 value of 0.37 mM, a value that is much higher than that of whole-cell currents. Current amplitudes decreased above 1 mM [Ca2+]i, (IC50 9.3 mM). Sr2+ but not Ba2+could partially substitute for Ca2+. ATP, ADP, AMP and AMP-PNP all quickly and reversibly inhibited TRPM4 with IC50 values between 2 and 19 μM (at +100 mV). Adenosine also blocked TRPM4 at 630 μM. The block at high ATP concentrations was incomplete and was not affected by the presence of free Mg2+. ADP induced the most sensitive block with an IC50 of 2.2 μM. For inhibition of TRPM4 by free ATP4−, an IC50 value of 1.7±0.3 μM was calculated. GTP, UTP and CTP at concentrations up to 1 mM did not induce a similar block. Spermine blocked TRPM4 currents with an IC50 of 61 μM. In conclusion, TRPM4 is a channel that can be effectively modulated by intracellular nucleotides and polyamines.
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Acknowledgements
We thank Drs. J.-P. Kinnet and P. Launay (Department of Pathology, Harvard Medical Scholl, Boston, Mass., USA) for providing us with the tetracycline-inducible HEK 293 Flag-TRPM4-expressing cell line. This work was supported by the Belgian Federal Government, the Flemish Government, the Onderzoeksraad KU Leuven (GOA 99/07, F.W.O. G.0214.99, F.W.O. G. 0136.00; F.W.O. G.0172.03, Interuniversity Poles of Attraction Program, Prime Ministers Office IUAP) .
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Nilius, B., Prenen, J., Voets, T. et al. Intracellular nucleotides and polyamines inhibit the Ca2+-activated cation channel TRPM4b. Pflugers Arch - Eur J Physiol 448, 70–75 (2004). https://doi.org/10.1007/s00424-003-1221-x
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DOI: https://doi.org/10.1007/s00424-003-1221-x