Intracellular nucleotides and polyamines inhibit the Ca2+-activated cation channel TRPM4b.
TRPM4b (in contrast to the short splice variant TRPM4a) is a Ca(2+)-activated but Ca(2+)-impermeable cation channel. We have studied TRPM4 currents in inside-out patches. Supramicromolar Ca(2+) concentrations applied at the inner side, [Ca(2+)](i), activated TRPM4 with an EC(50) value of 0.37 mM, a value that is much higher than that of whole-cell currents. Current amplitudes decreased above 1 mM [Ca(2+)](i), (IC(50) 9.3 mM). Sr(2+) but not Ba(2+)could partially substitute for Ca(2+). ATP, ADP, AMP and AMP-PNP all quickly and reversibly inhibited TRPM4 with IC(50) values between 2 and 19 microM (at +100 mV). Adenosine also blocked TRPM4 at 630 microM. The block at high ATP concentrations was incomplete and was not affected by the presence of free Mg(2+). ADP induced the most sensitive block with an IC(50) of 2.2 microM. For inhibition of TRPM4 by free ATP(4-), an IC(50) value of 1.7+/-0.3 microM was calculated. GTP, UTP and CTP at concentrations up to 1 mM did not induce a similar block. Spermine blocked TRPM4 currents with an IC(50) of 61 microM. In conclusion, TRPM4 is a channel that can be effectively modulated by intracellular nucleotides and polyamines.
Nilius
Bernd
B
Laboratorium voor Fysiologie Campus Gasthuisberg, KU Leuven, Herestraat 49, 3000 Leuven, Belgium. bernd.nilius@med.kuleuven.ac.be
Prenen
Jean
J
Voets
Thomas
T
Droogmans
Guy
G
D000227:Adenine Nucleotides / Q000494:pharmacology*; D002118:Calcium / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism; D027682:Cation Transport Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D002460:Cell Line; D002478:Cells, Cultured; D006801:Humans; D020128:Inhibitory Concentration 50; D007668:Kidney / Q000196:embryology / Q000378:metabolism; D018408:Patch-Clamp Techniques; D013096:Spermine / Q000494:pharmacology*; D050053:TRPM Cation Channels
D000227:Adenine Nucleotides; D015220:Calcium Channels; D027682:Cation Transport Proteins; D050053:TRPM Cation Channels; C437888:TRPM4 protein, human; D013096:Spermine; D002118:Calcium