Regulation of the Ca2+ sensitivity of the nonselective cation channel TRPM4.
TRPM4, a Ca(2+)-activated cation channel of the transient receptor potential superfamily, undergoes a fast desensitization to Ca(2+). The mechanisms underlying the alterations in Ca(2+) sensitivity are unknown. Here we show that cytoplasmic ATP reversed Ca(2+) sensitivity after desensitization, whereas mutations to putative ATP binding sites resulted in faster and more complete desensitization. Phorbol ester-induced activation of protein kinase C (PKC) increased the Ca(2+) sensitivity of wild-type TRPM4 but not of two mutants mutated at putative PKC phosphorylation sites. Overexpression of a calmodulin mutant unable to bind Ca(2+) dramatically reduced TRPM4 activation. We identified five Ca(2+)-calmodulin binding sites in TRPM4 and showed that deletion of any of the three C-terminal sites strongly impaired current activation by reducing Ca(2+) sensitivity and shifting the voltage dependence of activation to very positive potentials. Thus, the Ca(2+) sensitivity of TRPM4 is regulated by ATP, PKC-dependent phosphorylation, and calmodulin binding at the C terminus.
Nilius
Bernd
B
Department of Physiology, Campus Gasthuisberg, KU Leuven, B-3000 Leuven, Belgium. bernd.nilius@med.kuleuven.ac.be
Prenen
Jean
J
Tang
Jisen
J
Wang
Chunbo
C
Owsianik
Grzegorz
G
Janssens
Annelies
A
Voets
Thomas
T
Zhu
Michael X
MX
D000255:Adenosine Triphosphate / Q000494:pharmacology; D001665:Binding Sites; D002118:Calcium / Q000494:pharmacology*; D015220:Calcium Channels / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D002147:Calmodulin / Q000378:metabolism; D027682:Cation Transport Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D002460:Cell Line; D004594:Electrophysiology; D006801:Humans; D009154:Mutation; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D050053:TRPM Cation Channels
D015220:Calcium Channels; D002147:Calmodulin; D027682:Cation Transport Proteins; D050053:TRPM Cation Channels; C437888:TRPM4 protein, human; D000255:Adenosine Triphosphate; D011493:Protein Kinase C; D002118:Calcium