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Aims: Gut‐associated lymphoid tissue (GALT) carcinoma is a rare colorectal tumour that arises in the epithelium covering GALT. GALT carcinoma is a differentiated tubular adenocarcinoma with dense lymphoid tissue with a characteristically well‐demarcated margin. To date, 26 cases of GALT carcinoma, including the three cases discussed here, have been reported. Most (24 of 26) were discovered at early stages and none of the cases have documented any metastases. This suggests that GALT carcinoma may have a favourable prognosis. It is hypothesised that GALT carcinoma originates from M cells in specialised epithelia covering GALT. However, this hypothesis has yet to be confirmed. Methods and results: In this study, we examined three cases of GALT carcinoma by immunohistochemistry detection of glycoprotein 2, a specific marker for M cells, and electron microscopy. Our findings showed that the tumour cells of GALT carcinoma in all three cases were negative for M cells. We thus concluded that GALT carcinoma may be a tubular adenocarcinoma arising by chance in the GALT. This unique carcinoma is a diferentiated adenocarcinoma that grows slowly with the development of GALT. Conclusions: We propose that GALT carcinoma should be classified separately because of its histological setting and good prognosis. [ABSTRACT FROM AUTHOR]

Background Hypertrophic cardiomyopathy (HCM) is the most common monogenic cardiac disorder encountered in the clinic. Data relative to the electrophysiologic characteristics and pharmacologic responsiveness of human tissues and cells isolated from patients with HCM are rare. As a consequence, cellular mechanisms underlying arrhythmogenicity are poorly understood. Methods Cardiomyocytes were enzymatically dissociated from a septal myectomy surgically removed from a patient with obstructive HCM. Sharp microelectrodes and patch-clamp techniques were used to evaluate action potential and sodium channel current (INa) characteristics. Results Action potential morphology recorded was typical of an M cell, but with a longer than normal duration (APD) and a relatively steep APD-rate relationship. APD at all rates was significantly reduced following exposure to ranolazine (10 μM). Whole cell patch-clamp recording yielded robust peak INa and large late INa (1.1% of peak INa vs 0.1-0.2% in healthy controls). A large window current was observed as well. Ranolazine (10 μM) shifted steady-state V0.5 of inactivation by -8 mV, reduced late INa by 82%, and significantly diminished the window current. Conclusion Our results indicate the presence of cells with M-cell characteristics in the septum of the human heart, as has previously been described in the canine heart. They also point to an ameliorative effect of ranolazine to reduce augmented late INa and thus to reduce the prolonged APD in the setting of HCM. These results suggest a potential therapeutic role for ranolazine in HCM. [ABSTRACT FROM AUTHOR]

J Oral Pathol Med (2010) 39: 533–539 Objective: Membranous (M) cell of the human palatine tonsil is an antigen entry site for mucosal infection, but its location is obscure in histological sections. Recently, a microarray analysis has demonstrated that clusterin, annexin A5, CD44, MMP14, and β-tubulin are candidate genes of M cell marker in mice. Among these genes, we here describe class II β-tubulin as a new marker for human tonsillar M cells and follicular dendritic cells (FDCs), and present its usefulness for diagnosis of angioimmunoblastic T-cell lymphomas (AILTs). Materials and methods: Immunohistochemistry and Western blotting for class II β-tubulin were performed using 81 cases of lymphoid, gastrointestinal and thyroid tissues, and an FDC cell line, respectively. Double immunostaining with clusterin and class II β-tubulin were carried out. Results: Class II β-tubulin localized the M cells and FDCs in the palatine tonsils (10/10, 100%) and adenoids (10/10, 100%). It was colocalized with clusterin in the palatine tonsils. However, class II β-tubulin staining did not identify intestinal M cells in the intestines. Immunoblot analysis revealed that class II β-tubulin expression was upregulated in HK cells, a normal FDC cell line. Class II β-tubulin immunostaining highlighted hyperplastic FDC meshworks in all AILTs (14/14, 100%). Conclusion: Class II β-tubulin is a specific histochemical marker for human tonsillar M cells and FDCs. Thus, class II β-tubulin immunostaining may be useful to identify tonsillar M cells and to diagnose FDC proliferative lesions such as AILT. [ABSTRACT FROM AUTHOR]

The pyloric tonsil is a novel peripheral lymphoepithelial organ of the gastrointestinal tract in the chicken. It forms a complete lymphoid ring at the beginning of the duodenum, where crypts of Lieberkühn are transformed to tonsillar crypts with lymphoepithelial lining. The oesophageal (described previously) and pyloric tonsils are characteristic of the chicken, while they are absent in mammals. The lymphoid system develops from the middle germ layer, the mesoderm, and forms connections with the ecto- and endoderm, namely the skin and gut, respectively. These connections are based on the lymphoepithelial lining of the crypts, and provide gates for environmental antigens. Recent findings, taken together with the literature, suggest that in birds the lymphoid system forms connections with the endoderm-derived organs that are anatomically and histologically more extensive than the ectoderm-derived ones, which may be explained by the absence of regional lymph nodes, and the less developed lymphoid circulation of the skin. [ABSTRACT FROM AUTHOR]

Ventricular myocardium in larger mammals has been shown to be comprised of three distinct cell types: epicardial, M, and endocardial. Epicardial and M cell action potentials differ from endocardial cells with respect to the morphology of phase 1. These cells possess a prominent Ito-mediated notch responsible for the "spike and dome" morphology of the epicardial and M cell response. M cells are distinguished from the other cell types in that they display a smaller IKs, but a larger late INa and INa-Ca. These ionic distinctions underlie the longer action potential duration (APD) and steeper APD-rate relationship of the M cell. Difference in the time course of repolarization of phase 1 and phase 3 are responsible for the inscription of the electrocardiographic J wave and T wave, respectively. These repolarization gradients are sensitively modulated by electrotonic communication among the three cells types, [K+]o, and the presence of drugs that either reduce or augment net repolarizing current. A reduction in net repolarizing current generally leads to a preferential prolongation of the M cell action potential, responsible for a prolongation of the QT interval and an increase in transmural dispersion of repolarization (TDR), which underlies the development of torsade de pointes arrhythmias. An increase in net repolarizing current can lead to a preferential abbreviation of the action potential of epicardium in the right ventricle (RV), and endocardium in the left ventricle (LV). These actions also lead to a TDR that manifests as the Brugada syndrome in RV and the short QT syndrome in LV. [ABSTRACT FROM AUTHOR]

The cell strain M, which was established from normal rat liver cells, is characterized by the active formation of a collagen fiber network. In this study, we investigated the characterization of M cells and evaluated the anti-fibrogenic effects of taurine using this culture system. M cells expressed cytokeratin (CK)8, CK18, vimentin, and α-smooth muscle actin, whereas expression of CK-19 or desmin was not detected. Also, M cells expressed transforming growth factor (TGF)-β1, -β2, and TGF-β type I and II receptors, and treatment with TGF-β1 (1 ng/ml) for 6 days markedly stimulated the formation of a collagen fiber network and expression of procollagen α1(I) mRNA. When M cells were treated with various concentrations of taurine (10–50 mM), network formation and procollagen α1(I) expression were significantly suppressed in a dose dependent manner. Additionally, even in the presence of TGF-β1, taurine treatment effectively reduced the formation of a collagen fiber network. These results suggest that M cells exhibit features of not only hepatocytes but also myofibroblasts, and TGF-β1 plays an important role in the formation of collagen fiber networks in this culture system. Additionally, this M cell culture system is appropriate for use as an in vitro model of hepatic fibrosis in the evaluation of the anti-fibrogenic effects of various agents. [Copyright &y& Elsevier]

Introduction: Previous studies from our laboratory demonstrated (1) a much larger IΚs and (2) inability to induce early afterdepolarization (EAD) activity in epicardial and endocardial cells versus M cells. This study tests the hypothesis that these two characteristics are interrelated. Methods and Results: Standard and floating microelectrode techniques were used to record transmembrane activity from the canine left ventricular epicardial, M, and endocardial regions in isolated tissue slices and arterially perfused wedge preparations. The IΚr blocker E-4031 (1 to 10 µM) caused prominent prolongation of action potential duration (APD) and induced EADs in tissues isolated from the M region, but not those from epicardium or endocardium, causing a large transmural dispersion of APD. In contrast, the IΚs blocker chromanol 293B (10 to 30 µM) produced moderate prolongation of APD without EADs in all three tissue types. The combination of E-4031 (1 µM) and chromanol 293B (30 µM) resulted in profound prolongation of APD and the development of EADs in all three tissue types. In the perfused wedge, neither E-4031 nor chromanol 293B alone could induce EADs. In combination, the two drugs caused significant prolongation of APD and EADs in ail three transmural regions. Conclusion: Our results support the hypothesis that a prominent IΚs is responsible for the ability of epicardium and endocardium to resist some but not all of the arrhythmogenic effects of IΚr block. The data highlight the critical importance of IΚs, in the canine heart and the significant role of electrotonic interactions in minimizing the development of an arrhythmogenic substrate when repolarization reserve is reduced. [ABSTRACT FROM AUTHOR]

Introduction: A growing number of cardiomyopathies have been shown to result in a reduction in both IKr and IKs, jet little is known about the electrophysiologic and ECG characteristics of combined IKr and IKs block. Methods and Results: To address this gap in our knowledge, transmembrane action potentials (APs) from epicardial, M, and endocardial cells were recorded simultaneously, together with a transmural ECG from arterially perfused canine left ventricular wedge preparations exposed to combined IKr(d-sotalol; 100 µ-mol/L) and IKs (chromanol 293B; 30 to 60 µmol/L) block. Under baseline conditions, the T wave was typically upright; epicardium repolarized first, coinciding with the peak of the T wave, and the M cells repolarized last, coinciding with the end of the T wave (Tend)- Complex (inverted, biphasic, and triphasic) T waves developed following combined IKr and IKs block. M and epicardial APs prolonged dramatically, so that the endocardial AP was now the earliest to repolarize, coinciding with the first nadir of the complex T wave. In the case of biphasic/triphasic or inverted T waves, Tend coincided with repolarization of either M or epicardial cells, whichever was the last to repolarize. QT intervals prolonged from 286 ± 13 msec up to 744 ± 148 msec and transmural dispersion of repolarization (TDR) increased from 33 ± 10 msec up to 244 ± 71 msec. Early afterdepolarizations (EADs) developed in M and epicardial cells, evoking extrasystoles that precipitated polymorphic ventricular tachycardia. Acceleration-induced EADs and T wave alternans also were observed. Conclusion: Combined IKr and IKs block gives rise to inverted, biphasic, and triphasic T wave morphologies, a dramatic increase in TDR, and a high incidence of EADs. The diversity of T wave morphologies derives from a preferential AP prolongation of different transmural layers leading to variation in the predominance of voltage gradients on either side of the M cell region. Our study provides direct evidence linking EADs that arise in ventricular epicardial and M cells to the triggered beats that precipitate polymorphic ventricular tachycardia. Our results also suggest possible guidelines for the estimation of TDR from complex T waves appearing in the precordial leads of the surface ECG. [ABSTRACT FROM AUTHOR]

Introduction: An early afterdepolarization (EAD)-induced triggered beat is thought to precipitate torsade de pointes (TdP) in the long QT syndrome (LQTS). Previous studies demonstrated the development of EAD activity and dispersion of repolarization under LQT2 (reduced IKr ) and LQT3 (augmented late INa), but not LQT1 (reduced IKs), conditions. The present study examines these electrophysiologic characteristics during IKs block. Methods and Results: Canine epicardial (Epi), M, and endocardial (Endo) tissues and Purkinje fibers isolated from the canine left ventricle were studied using standard microelectrode recording techniques. The IKs blocker chromanol 293B (293B, 30 μM), produced a homogeneous rate. independent prolongation of action potential duration (APD) in Epi, M, and Endo, but little to no APD prolongation in Purkinje. Chromanol 293B 1 to 30 μM failed to induce EADs or delayed afterdepolarizations (DADs) in any of the four tissue types. Isoproterenol (ISO, 0.1 to 1.0 μM) in the presence of 293B 30 μM significantly prolonged the APD of the M cell (basic cycle length ≥ 1 sec), abbreviated that of Purkinje, and caused little change in that of Epi and Endo. The combination of 293B 30 μM and ISO 0.2 μM did not induce EADs in any of the four tissue types, but produced DAD activity in 4 of 8 Epi, 7 of 10 M cells, and 3 of 8 Endo. Conclusion: Our results indicate that IKs block alone or in combination with β-adrenergic stimulation does not induce EADs in any of the four canine ventricular tissue types, but that the combination of the two induces DADs as well as accentuated dispersion of repolarization. [ABSTRACT FROM AUTHOR]

Transmural Dispersion of Repolarization In Vivo. Introduction: In vitro studies have provided evidence for the existence of M cells. The present study examines the contribution of the M cell to transmural dispersion of repolarization (TDR) and to the development of torsades de pointes (TdP) in the canine heart in vivo in animals anesthetized with either pentobarbital or halothane. [ABSTRACT FROM AUTHOR]

Introduction: Sodium pentobarbital is widely used for anesthesia in experimental studies as well as in clinics, and it is known to prevent the development of torsades de pointes (TdP) in in vivo models of the long QT syndrome (LQTS). Methods and Results: This study examines the effects of pentobarbital on transmural dispersion of repolarization (TUR) and induction of TdP in arterially perfused canine left ventricular wedge preparations in which transmembrane action potentials were simultaneously recorded from epicardial, M, and endocardial regions using floating glass microelectrodes together with a transmural ECG. d-Sotalol and ATX-Il were used to mimic the LQT2 and LQT3 forms of congenital LQTS. Both d-Sotalol (100 μmol/L, n = 6) and ATX-II (20 nmol/L, n = 6) preferentially prolonged the action potential duration (APD90) of the M cell, thus increasing in the QT interval and TDR, and leading to the development of spontaneous and stimulation-induced TdP. In the absence and presence of d-sotalol, pentobarbital (10, 20, and 50 μg/mL) prolonged the APD90 of epicardial and endocardial cells, and, to a lesser extent, that of the M cell, thus prolonging the QT interval but reducing TDP. In the ATX-II model, the effects of pentobarbital on the QT interval and APD% were biphasic: 10 μg/mI, pentobarbital further prolonged APD90 of epicardial and endocardial cells more than that of the M cell; 20 to 50 μg/mL pentobarbital abbreviated the APD90 of epicardial and endocardial cells less than that of the M cell, thus abbreviating the QT interval and markedly reducing TDR. Twenty to 50 μg/mL pentoharbital totally suppressed spontaneous as well as stimulation-induced TdP in both models. Conclusion: Our data indicate that pentobarbital reduces TDR in control and under conditions of congenital and acquired LQTS, and suggest that this mechanism may contribute to the ability of the anesthetic to prevent the development of spontaneous as well as stimulae (ion-induced TdP under conditions mimicking JQT2, LQT3, and acquired (drug-induced) forms of the LQTS. The data also serve to illustrate that there are circumstances under which QT prolongation may not be arrhythmogenic. [ABSTRACT FROM AUTHOR]

Introduction: Cytochalasin D In tissue bath superfusate inhibits the contraction of isolated thin trabeculae from canine right ventricle without affecting the intracellular action potential recorded with glass microelectrode. The purpose of this study was to test whether cytochalasin D could also be used to immobilize perfused wedges of ventricular muscle without affecting the action potential duration or propagation, and also to determine the optimal concentration and time duration of drug in the perfusate. Methods and Results: Using a membrane potential sensitive dye, di-4-ANEPPS, and a high-resolution photodiode optical mapping system at a rate of 1,000 frames/sec, we recorded action potentials on the transmural surface of arterially perfused wedges of muscle from the canine left ventricular free wall. We also recorded arterial pulse pressure as a surrogate for tissue contraction. Cytochalasin D at ≥ 20 μ mol/L in the perfusate for ≥ 6 minutes reduced the arterial pulse pressure to approximately one tenth of its initial value and significantly reduced or eliminated motion artifacts in the action potentials. A sustained concentration of 10 μmol/L cytocbalasin D in the perfusate prevented contraction from recurring after the tissue was immobilized with an initial concentration of 25 μmol/L. Cytochalasin D had little effect on the action potential duration and on its transmural gradient, and did not slow the transmural velocity of excitation propagation. Conclusion: Cytochalasin D can be used to uncouple excitation and contraction in perfused canine cardiac muscle for the fluorescent-optical mapping of action potentials without affecting action potential duration or slowing transmural propagation. [ABSTRACT FROM AUTHOR]

Introduction: Precipitation of torsades de pointes (TdP) has been shown to be associated with acceleration of heart rate in both experimental and clinical studies. To gain insight into the cellular mechanism(s) responsible for the initiation of acceleration-induced TdP, we studied the effect of acceleration of pacing rate in canine left ventricular epicardial, M region, endocardial, and Purkinje fiber preparations pretreated with E-4031, an IKr blocker known to induce the long QT syndrome and TdP. Methods and Results: Standard microelectrode techniques were used. E.4031 (1 to 2 µM) induced early afterdepolarization (EAD) activity in 31 of 36 M cell, 0 of 10 epicardial, 0 of 10 endocardial, and 9 of 12 Purkinje fiber preparations at basic cycle lengths (BCLs) ≥ 800 msec. In 30 of 36 M cells, sudden acceleration from a BCL range of 900 to 4,000 msec to a range of 500 to 1,500 msec induced transient EAD activity if none existed before or increased the amplitude of EADs if already present. Acceleration-induced augmentation of EAD activity was far less impressive and less readily demonstrable in Purkinje fibers (4/12). In M cells, appearance of EAD activity during acceleration usually was accompanied by an abbreviation of action potential duration (APD). Within discrete ranges of rates in the physiologic range, acceleration caused a transient prolongation of APD in 38% of M cells, whether or not a distinct EAD was generated. Acceleration produced still more dramatic APD prolongation and EADs in M cells after the BCL was returned to the original slow rate. Epicardium and endocardium APD showed little change immediately after acceleration. A decrease of BCL as small as 10% and, in some cases, a single premature beat could promote EAD activity and APD prolongation in some M cells. Ryanodine (1 µM, 10/10), flunarizine (10 µM, 3/6), and low Na (97 vs 129 mM, 5/5) abolished the acceleration-induced EAD activity and APD prolongation as well as the EAD activity observed at slow rates in M cells pretreated with E-4031. Conclusion: Our results suggest that acceleration from an initially slow rate or a single premature beat can induce or facilitate transient EAD activity and APD prolongation in canine ventricular M cell preparations pretreated with an IKr blocker via a mechanism linked to intracellular calcium loading. Our data provide evidence in support of an important contribution of electrogenic Na/Ca exchange current to this process. These acceleration-induced changes can result in the development of triggered activity as well as a marked dispersion of repolarization in ventricular myocardium and, thus, may contribute to the precipitation of TdP in patients with the congenital (HERG defect) and acquired (drug-induced) long QT syndrome. [ABSTRACT FROM AUTHOR]

Ventricular myocardium in larger mammals is composed of three distinct cell types: epicardial, M, and endocardial cells. Epicardial and M cell, but not endocardial cell, action potentials have a prominent Ito-mediated notch. M cells are distinguished from the other cell types in that they display a smaller IKs, but a larger late INa and INa–Ca. These ionic differences may account for the longer action potential duration (APD) and steeper APD-rate relationship of the M cell. The difference in the time course of repolarization of phase 1 and phase 3 contributes to the inscription of the electrocardiographic J wave and T wave, respectively. These repolarization gradients are modulated by electrotonic interactions, [K+]o, and agents or mutations that alter net repolarizing current. An increase in late INa, as occurring under a variety of pathophysiological states or in response to certain toxins, leads to a preferential prolongation of the M cell action potential, thus prolonging the QT interval and increasing transmural dispersion of repolarization (TDR), which underlies the development of torsade de pointes (TdP) arrhythmias. Agents that reduce late INa are effective in reducing TDR and suppressing TdP. A reduction in peak INa or an increase in net repolarizing current in the early phases of the action potential can lead to a preferential abbreviation of the action potential of epicardium in the right ventricle, and thus the development of a large TDR, phase 2 reentry, and polymorphic ventricular tachycardia associated with the Brugada syndrome. [ABSTRACT FROM AUTHOR]

Introduction: The apparent location of the myocytes (M cells) with the longest action potential duration (APD) in a canine left ventricular (LV) wedge have been reported to shift after application of a sea anemone toxin, ATX-II. This toxin slows inactivation of INa and thus prolongs APD. Thus, M cells may exhibit dynamic functional states, rather than being a static, anatomically discrete, myocyte population. In this study, we attempted to further define and understand this phenomenon using a mathematical model of the human ventricular myocyte action potential incorporated into an in silico “wedge” preparation. Our simulations demonstrate that even under conditions of a fixed population and ratio of epicardial, M, and endocardial myocytes, the apparent anatomical position (transmural location) of the myocytes with the longest APD can shift following ATX-II treatment. This arises because the ATX-II effect, modeled as a small increase in the late or persistent Na+ current, and consequent prolongation of APD significantly changes the electrotonic interactions between ventricular myocytes in this LV wedge preparation. Methods and Results: This LV wedge model is based on bidomain equations. It corresponds to a rectangular tissue immersed in a passive and isotropic medium that represents the superfusion bath. In this theoretical work, the three known different and discrete populations of myocytes in the human left ventricle have been included: the epicardial, M, and endocardial cells. The effects of ATX-II on INa were simulated by altering the voltage-dependent steady-state inactivation of the parameters h (fast gate) and j (slow gate). As a result, in these ATX-II simulations a persistent late Na+ current was generated in all three types of ventricular myocytes. However, the APDs were prolonged in a heterogeneous pattern. Our simulations demonstrate that after the ATX-II effects develop, alterations in transmural electrotonic interactions can produce changes in the transmural location of myocytes with the longest APD. Conclusions: The combination of intercellular electrotonic interactions, which tend to reduce and smooth out the discrete transmural APD variations, and the heterogeneous effects of ATX-II, which preferentially prolong the APD of M cells, can shift the location of the ventricular myocytes. This shift results in significantly altered transmural patterns of action potential durations, which would be expected to change localized refractory period and excitability. These cellular changes give rise to alterations in the corresponding surface electrograms and may change the overall substrates for conduction and rhythm disturbances. [ABSTRACT FROM AUTHOR]