1. Point: M cells are present in the ventricular myocardium
Lance D. Wilson, M.D., Michelle M. Jennings, B.S., David S. Rosenbaum, M.D., F.H.R.S. 
Heart Rhythm 
Volume 8, Issue 6, Pages (June 2011)
DOI: /j.hrthm
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2. Figure 1
Action potentials of three transmural cell types: epicardial (Epi), M cell, and endocardial (Endo).1 Both Epi and M show characteristic spike-and-dome morphology. Importantly, the M cell action potential duration markedly prolongs in response to slowing of heart rate. BCL = basic cycle length.
Heart Rhythm 2011 8, DOI: ( /j.hrthm )
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3. Figure 2
Evolving concepts regarding transmural gradients of repolarization. A: Various models of transmural action potential duration (APD) heterogeneity are illustrated schematically. B: The APD profile is a one-dimensional representation of the transmural APD gradient generated from APD measured along the dashed line in the corresponding schematic in panel A. Classically (black), it was proposed that APD prolonged monotonically from epicardium to endocardium, with no midmyocardial APD zenith characteristic of M cells.4 Later, it was hypothesized the M cells form discrete uniform bands in midmyocardium (green).1 When accounting for intercellular coupling in multicellular preparations,2,5 APD gradients produced by M cells are smoothed (blue). In heart failure (red), APD prolongs and there is a steeper APD gradient (solid arrow).6 ENDO = endocardial; EPI = epicardial; HF = heart failure; MID = midmyocardial.
Heart Rhythm 2011 8, DOI: ( /j.hrthm )
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4. Figure 3
M-cell topology determines magnitude and location of arrhythmogenic repolarization gradients. A: Transmural action potential duration (APD) map from a canine wedge preparation. Note that due to the topography of M cells, varying location of the plunge electrode can significantly alter the APD profile measured. B: Transmural APD map from a different wedge preparation displaying a different M-cell topology than that shown in panel A.2 C: APD map from human wedge preparation showing evidence for M cells in islandlike topology.7 D: Transmural repolarization gradients promote arrhythmias by causing conduction block at the epicardial–midmyocardial interface.6 ENDO = endocardial; EPI = epicardial; MID = midmyocardial.
Heart Rhythm 2011 8, DOI: ( /j.hrthm )
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