title: Implication of the TRPM4 nonselective cation channel in mammalian sinus rhythm.
abstract: BACKGROUND
  The transient receptor potential melastatin 4 (TRPM4) channel is expressed in the sinoatrial node, but its physiologic roles in this tissue with cardiac pacemaker properties remain unknown. This Ca(2+)-activated nonselective cation channel (NSCCa) induces cell depolarization at negative potentials. It is implicated in burst generation in neurons and participates in induction of ectopic beating in cardiac ventricular preparations submitted to hypoxia/reoxygenation. Accordingly, TRPM4 may participate in action potential (AP) triggering in the sinoatrial node.
  
  
  OBJECTIVE
  The purpose of this study was to investigate the influence of TRPM4 on spontaneous heart beating.
  
  
  METHODS
  Spontaneous APs were recorded using intracellular microelectrodes in mouse, rat, and rabbit isolated right atria.
  
  
  RESULTS
  In the spontaneously beating mouse atrium, superfusion of the TRPM4-specific inhibitor 9-phenanthrol produced a concentration-dependent reduction in AP rate (maximal reduction = 62% that of control; EC50 = 8 × 10(-6) mol●L(-1)) without affecting other AP parameters. These effects were absent in TRPM4(-/-) mice. 9-Phenanthrol exerted a rate-dependent reduction with a higher effect at low rates. Similar results were obtained in rat. Moreover, application of 9-phenanthrol produced a reduction in diastolic depolarization slope in rabbit sinus node pacemaker cells.
  
  
  CONCLUSIONS
  These data showed that TRPM4 modulates beating rate. Pacemaker activity in the sinoatrial node results from the slow diastolic depolarization slope due to the "funny" current, Na/Ca exchange, and a Ca(2+)-activated nonselective cation current, which can be attributable in part to TRPM4 that may act against bradycardia.
authors: Normandie Université, EA 4650, Groupe Signalisation, Electrophysiologie et Imagerie des Lésions d'Ischémie-Reperfusion Myocardique, UCBN, Caen, France.
authors: Thomas
authors: T
authors: Hof
authors: Christophe
authors: C
authors: Simard
authors: René
authors: R
authors: Rouet
authors: Laurent
authors: L
authors: Sallé
authors: Romain
authors: R
authors: Guinamard
mesh_terms: D000818:Animals; D001919:Bradycardia / Q000378:metabolism / Q000503:physiopathology / Q000628:therapy*; D004195:Disease Models, Animal; D005260:Female; D005786:Gene Expression Regulation; D006325:Heart Atria / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018408:Patch-Clamp Techniques; D010616:Phenanthrenes / Q000494:pharmacology*; D047428:Protein Kinase Inhibitors; D011817:Rabbits; D051381:Rats; D012849:Sinoatrial Node / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology*; D050053:TRPM Cation Channels / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000235:genetics
chemical_list: D010616:Phenanthrenes; D047428:Protein Kinase Inhibitors; D050053:TRPM Cation Channels; C476766:TRPM4 protein, mouse; C091375:9-phenanthrol
keywords: AP; APA; APD(50); APD(70); APD(90); Bradycardia; Ca(2+)-activated nonselective cation channel; Ca(2+)-activated nonselective cation channels; DD; EC(50); Heart rate; I(Ca,L); I(Ca,T); I(f); L-type Ca(2+) current; NSC(Ca); RMP; SAN; Sinus node; T-type Ca(2+) current; TRPM; Transient receptor potential melastatin 4; V(max); WT; action potential; action potential amplitude; action potential duration at 50% repolarization; action potential duration at 70% of repolarization; action potential duration at 90% of repolarization; concentration for half maximal effect; diastolic depolarization; funny current; maximum upstroke velocity; resting membrane potential; sinoatrial node; transient receptor potential melastatin; wild type