title: Lack of evidence of M-cells in porcine left ventricular myocardium.
abstract: OBJECTIVE
  The aim of this study was to analyze whether cells with long action potential duration, fast Vmax, and spike-and-dome configuration (M-cells) are present in porcine left ventricular myocardium.
  
  
  METHODS
  Transmembrane action potentials (n = 505) of the left ventricle were recorded with conventional glass microelectrodes in an epicardial-endocardial direction at 2000 ms basic cycle length in 14 pigs. In 3 pigs, potentials were obtained at 1000, 2000, and 5000 ms cycle length before and after superfusion with quinidine HCl 1 microgram/ml. In addition, transmembrane potentials (n = 52) were recorded in 4 dogs at 2000 ms cycle length to verify the ability of our protocol to detect M-cells.
  
  
  RESULTS
  In pigs, action potential duration at 90% repolarization was shorter (ANOVA, P < 0.001) and Vmax slower (P < 0.001) in the epicardium than in the other transmural sites, but there were no regional differences in resting membrane potential or in action potential amplitude. Potentials with particularly long phase 3 or with spike-and-dome configuration were not observed. All myocardial sites displayed rate dependence of action potential duration (P = 0.02) which was transmurally homogeneous and persisted after quinidine exposure. The drug did not induce afterdepolarizations. In dogs, potentials with spike-and-dome configuration, long duration, and fast Vmax, like those described in M-cells, were detected in deep epicardial and midmyocardial areas.
  
  
  CONCLUSIONS
  The porcine left ventricular myocardium shows transmural differences in action potential duration and Vmax, but, unlike dogs, it lacks M-cells.
authors.affiliation: Laboratorio de Cardiología Experimental, Hospital General Universitari Vall d'Hebron, Universitat Autònoma de Barcelona, Spain.
authors.forename: A
authors.initials: A
authors.lastname: Rodríguez-Sinovas
authors.forename: J
authors.initials: J
authors.lastname: Cinca
authors.forename: A
authors.initials: A
authors.lastname: Tapias
authors.forename: L
authors.initials: L
authors.lastname: Armadans
authors.forename: M
authors.initials: M
authors.lastname: Tresànchez
authors.forename: J
authors.initials: J
authors.lastname: Soler-Soler
mesh_terms: D000200:Action Potentials; D000704:Analysis of Variance; D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology; D004285:Dogs; D005260:Female; D008297:Male; D008564:Membrane Potentials; D010496:Pericardium / Q000166:cytology* / Q000502:physiology; D011802:Quinidine / Q000494:pharmacology; D013552:Swine / Q000033:anatomy & histology* / Q000502:physiology
chemical_list: D000889:Anti-Arrhythmia Agents; D011802:Quinidine