Lack of evidence of M-cells in porcine left ventricular myocardium.
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.
Rodríguez-Sinovas
A
A
Laboratorio de Cardiología Experimental, Hospital General Universitari Vall d'Hebron, Universitat Autònoma de Barcelona, Spain.
Cinca
J
J
Tapias
A
A
Armadans
L
L
Tresànchez
M
M
Soler-Soler
J
J
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
D000889:Anti-Arrhythmia Agents; D011802:Quinidine