Author + information
- Received June 10, 1994
- Revision received February 24, 1995
- Accepted March 14, 1995
- Published online July 1, 1995.
- Emmanuel Drouin, PhD,
- Flavien Charpentier, PhD,
- Chantal Gauthier, PhD,
- Karine Laurent, BS and
- Herve Le Marec, MD, PhD*
- ↵*Address for correspondence: Dr. Hervé Le Marec, Laboratory of Experimental Cardiology, UA CNRS 1340, Laënnec Hospital, BP 1005, 44035 Nantes Cedex, France.
Objectives. 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 ∼ 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.
This study was supported in part by Grant CRE INSERM 92-0412 from the Institut National de la Santé et de la Recherche Médicale, Paris, France.
- Received June 10, 1994.
- Revision received February 24, 1995.
- Accepted March 14, 1995.
- The American College of Cardiology