title: Electrophysiologic characteristics of cells spanning the left ventricular wall of human heart: evidence for presence of M cells.
abstract: OBJECTIVE
  The present work was designed to provide an initial characterization of M cells in the normal human heart.
  
  
  BACKGROUND
  Recent studies have uncovered a unique population of cells in the midmyocardial region of the canine ventricle. These cells, named M cells, were found to possess electrophysiologic features and a pharmacologic responsiveness different from those of other myocardial cells. Although well characterized in the dog, their presence or absence in the human heart is unknown.
  
  
  METHODS
  Standard microelectrode techniques were used to map slices of ventricular free wall obtained from normal human hearts (n = 4). Preparations were paced at cycle lengths ranging from 1 to 10 s.
  
  
  RESULTS
  We identified three cell subtypes: endocardial, subepicardial (M cells) and epicardial cells. The principal features differentiating M cells from the other cell subtypes were their longer action potential duration, more accentuated action potential duration rate relations and greater maximal rate of increase in action potential upstroke (Vmax). Our findings suggest that M cells represent approximately 30% of the cellular mass of the left ventricular wall. Concordance between changes in their repolarization and changes in QTU interval provide support for the role of M cells in the generation of the electrocardiographic (ECG) U wave.
  
  
  CONCLUSIONS
  This study provides evidence for the existence of M cells in the human heart that contribute to heterogeneity of repolarization within the ventricular wall. Our findings provide strong support for the hypothesis that M cells contribute importantly to the manifestation of the U wave on the ECG.
authors.affiliation: Laboratory of Experimental Cardiology, National Center for Scientific Research, Nantes, France.
authors.forename: E
authors.initials: E
authors.lastname: Drouin
authors.forename: F
authors.initials: F
authors.lastname: Charpentier
authors.forename: C
authors.initials: C
authors.lastname: Gauthier
authors.forename: K
authors.initials: K
authors.lastname: Laurent
authors.forename: H
authors.initials: H
authors.lastname: Le Marec
mesh_terms: D000200:Action Potentials; D000293:Adolescent; D000328:Adult; D004562:Electrocardiography; D004699:Endocardium / Q000166:cytology; D005260:Female; D006352:Heart Ventricles / Q000166:cytology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009206:Myocardium / Q000166:cytology*; D010496:Pericardium / Q000166:cytology; D016276:Ventricular Function