TRPM4, a Ca2+-activated nonselective cation channel in mouse sino-atrial node cells

Cardiovasc Res. 2007 Feb 1;73(3):531-8. doi: 10.1016/j.cardiores.2006.11.023. Epub 2006 Nov 22.

Abstract

Objective: A calcium-activated nonselective cation channel (NSC(Ca)) has been recently described in several cardiac preparations. This channel is over-expressed in models of ventricular hypertrophy showing electrophysiological perturbations of heart activity, including occurrence of spontaneous activity. While these perturbations are currently attributed to a modification of the pacemaker I(f) current activity, arguments are also in favor of participation of an NSC(Ca). Similarly, the NSC(Ca) may be expressed in specialized pacemaker cells, i.e. sino-atrial node (SAN) cells. The aim of the present study was to detect such current in mouse pacemaker cells.

Methods: The inside-out configuration of the patch-clamp technique was used in freshly isolated SAN cells from adult mice. Also, RT-PCR and Western-blotting studies were used to probe for TRPM4 mRNA and protein expression.

Results: In these cells, an NSC(Ca) activity was detected. The channel is voltage dependant with a conductance of 20.9+/-0.5 pS (n = 11). It is equally permeable for Na+ and K+ but does not conduct Ca2+. It is activated by rise in intracellular calcium concentrations and blocked by intracellular ATP (0.5 mmol/L). Also, as a new property in cardiac cells, the channel is activated by internal application of phosphatidylinositol 4,5-bisphosphate (10 microM). It is reversibly inhibited by flufenamic acid and glibenclamide. This channel shows the hallmarks of the TRPM4 molecule, a member of the TRP melastatin subfamily. We confirm the expression of this TRP channel on SAN cells by Western blotting and RT-PCR and validate that TRPM4 is glibenclamide sensitive.

Conclusion: TRPM4 is functionally expressed in SAN cells and may be a key player in the generation and/or perturbation of heart rhythm.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Anti-Inflammatory Agents, Non-Steroidal / pharmacology
  • Blotting, Western
  • Calcium Channel Blockers / pharmacology
  • Calcium Chloride / pharmacology
  • Cell Line
  • Cell Membrane / metabolism
  • Female
  • Flufenamic Acid / pharmacology
  • Glyburide / pharmacology
  • Humans
  • Ion Channel Gating / drug effects
  • Mice
  • Myocytes, Cardiac / chemistry
  • Myocytes, Cardiac / metabolism*
  • Patch-Clamp Techniques
  • Phosphatidylinositol 4,5-Diphosphate / pharmacology
  • RNA, Messenger / analysis
  • Reverse Transcriptase Polymerase Chain Reaction
  • Sinoatrial Node / chemistry
  • Sinoatrial Node / metabolism*
  • TRPM Cation Channels / analysis*
  • TRPM Cation Channels / genetics

Substances

  • Anti-Inflammatory Agents, Non-Steroidal
  • Calcium Channel Blockers
  • Phosphatidylinositol 4,5-Diphosphate
  • RNA, Messenger
  • TRPM Cation Channels
  • TRPM4 protein, human
  • Flufenamic Acid
  • Calcium Chloride
  • Glyburide