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PubMed1994

Dominant optic atrophy (OPA1) mapped to chromosome 3q region. I. Linkage analysis.

Dominant optic atrophy, type Kjer (McKusick no. 165500) is an autosomal dominant eye disease. The disease is characterized by moderate to severe visual impairment with an insidious onset during the first decade of life, blue-yellow dyschromatopsia and centrocecal scotoma of varying density. We examined three extended Danish pedigrees using highly informative short tandem repeat polymorphisms and found linkage of the disease gene (OPA1) to a (CA)n dinucleotide repeat polymorphism at locus D3S1314 (Zmax = 10.34 at theta M = F = 0.075). Using two additional chromosome 3 markers we were able to map the OPA1 gene in the region between D3S1314 and D3S1265 (3q28-qter).

Chromosome Mapping↗
PubMed2000

Synthetic strands of neonatal mouse cardiac myocytes: structural and electrophysiological properties.

The aim of the present study was to morphologically and electrically characterize synthetic strands of mouse ventricular myocytes. Linear strands of mouse ventricular myocytes with widths of 34.7+/-4.4 microm (W(1)), 57.9+/-2.5 microm (W(2)), and 86.4+/-3. 6 microm (W(3)) and a length of 10 mm were produced on glass coverslips with a photolithographic technique. Action potentials (APs) were measured from individual cells within the strands with cell-attached microelectrodes. Impulse propagation and AP upstrokes were measured with multisite optical mapping (RH237). Immunostaining was performed to assess cell-cell connections and myofibril arrangement with polyclonal antisera against connexin43 and N-cadherins and monoclonal antibodies against cardiac myosin. Light microscopy and myosin staining showed dense growth of well-developed elongated myocytes with lengths of 34.2+/-4.2 microm (W(1)), 36. 9+/-5.8 microm (W(2)), and 43.7+/-6.9 microm (W(3)), and length/width ratios of 3.9+/-0.2. Gap junctions were distributed around the cell borders (3 to 4 junctions/microm(2) cell area). Each cell was connected by gap junctions to 6.5+/-1.1 neighboring cells. AP duration shortened with time in culture (action potential duration at 50% repolarization: day 4, 103+/-34 ms; day 8, 16+/-3 ms; P:<0.01). Minimum diastolic potential and AP amplitude were 71+/-5 and 97.2+/-7.6 mV, respectively. Conduction velocity and the maximum dV/dt of the AP upstroke were 43.9+/-13.6 cm/s and 196+/-67 V/s, respectively. Thus, neonatal ventricular mouse myocytes can be grown in continuous synthetic strands. Gap junction distribution is similar to the neonatal pattern observed in the hearts of larger mammals. Conduction velocity is in the range observed in adult mice and in the higher range for mammalian species probably due to the higher dV/dt(max). This technique will permit the study of propagation, AP, and structure-function relations at cellular resolution in genetically modified mice.

Action Potentials↗
PubMed2001

Understanding conduction of electrical impulses in the mouse heart using high-resolution video imaging technology.

The conduction of electrical impulses in the heart depends on the ability to efficiently transfer excitatory current between individual myocytes. Several recent studies have focused on the use of optical mapping techniques to determine the electrophysiological consequences and the proarrhythmic effects of reducing intercellular coupling in newly developed connexin knockout mice. This work has begun to unravel important questions regarding the role of connexins in intercellular coupling and propagation of electrical impulses in the heart. The purpose of this review is to discuss the techniques and unique issues involved in imaging electrical wave propagation in the heart. In addition, we will review recent experimental studies that address the role of intercellular communication in the development of cardiac arrhythmias.

Animals↗
PubMed2004

The muscular network of the sheep right atrium and frequency-dependent breakdown of wave propagation.

The complex branching structure of the right atrium (RA) muscular network may provide the substrate for complex patterns of propagation during atrial fibrillation (AF). As AF results in some cases from stable sources in the left atrium (LA) with fibrillatory conduction toward the RA, we hypothesize that periodic input to the RA at an exceedingly high frequency results in disorganized wave propagation associated with the complex structure of the RA. Optical mapping was performed in isolated coronary-perfused sheep RA. Rhythmic pacing of Bachmann's bundle allowed well-controlled and realistic conditions for LA-driven RA. Pacing at increasingly higher frequencies led to increasing delays in activation distal to major branching sites of the Crista terminalis and pectinate bundles, culminating in spatially distributed intermittent blockade at and above approximately 6.5 Hz. At this breakdown frequency, the dominant frequencies of the RA response activity became spatially nonuniform. Such frequency-dependent changes were independent of action potential duration. Rather, the spatial boundaries between proximal and distal frequencies correlated well with branch sites of the pectinate musculature. Thus, there exists a breakdown frequency in the sheep RA below which activity is periodic throughout the atrium and above which it is fibrillation-like, consistent with the ideas that during AF, high-frequency activation initiated in the LA undergoes fibrillatory conduction toward the RA, and that sink-to-source mismatch effect at branch points of the Crista terminalis and pectinate muscles is important in determining the complexity of the arrhythmia.

Action Potentials↗
PubMed2004

Developmental transitions in electrical activation patterns in chick embryonic heart.

The specialized conduction tissue network mediates coordinated propagation of electrical activity through the adult vertebrate heart. Following activation of the atria, the activation wave is slowed down in the atrioventricular canal or node, then spreads rapidly into the left and right ventricles via the His-Purkinje system (HPS). This results in the ventricle being activated from the apex toward the base and is thought to represent HPS function. The development of mature HPS function in embryogenesis follows significant phases of cardiac morphogenesis. Initially, cardiac impulse propagates in a slow, linear, and isotropic fashion from the sinus venosus at the most caudal portion of the tubular heart. Although the speed of impulse propagation gradually increases, ventricular activation in the looped heart still follows the direction of blood flow. Eventually, the immature base-to-apex sequence of ventricular activation undergoes an apparent reversal, maturing to apex-to-base pattern. The embryonic chick heart has been studied intensively by both electrophysiological and morphological techniques, and the morphology of its conduction system (which is similar to mammals) is well characterized. One interesting but seldom studied feature is the anterior septal branch (ASB), which came sharply to focus (together with the rest of the ventricular conduction system) in our birthdating studies. Using an optical mapping approach, we show that ASB serves to activate ventricular surface between stages 16 and 25, predating the functionality of the His bundle/bundle branches. Heart morphogenesis and conduction system formation are thus linked, and studying the abnormal activation patterns could further our understanding of pathogenesis of congenital heart disease.

Action Potentials↗
PubMed2006

Three-dimensional anatomy of the conduction system of the early embryonic rabbit heart.

The complete embryonic cardiac conduction system is difficult to view in three dimensions, primarily because there has not been a marker of all segments of the normal system throughout all stages of development. Imaging of the conduction system components within the atria has been particularly controversial because different markers reveal different pathways that may or may not represent conduction system components. The conduction system of the adult and embryonic rabbit, however, can be labeled in its entirety with the neurofilament marker, NF-160. The conduction system of rabbit embryos at several stages of development spanning cardiac septation was therefore investigated. Optical mapping of the electrical signature of the conduction system previously revealed a close correlation between the cardiac activation patterns and the anatomy as shown by serial sections. The 3D relationship between the components of the conduction system could only be inferred from the 2D sections. The sections were consequently reconstructed using a commercial software program (AutoQuant). This is the first demonstration of the three-dimensional complete normal rabbit embryonic cardiac conduction system at several stages of development.

Animals↗
PubMed2005

Emerging patterns of cardiac conduction in the chick embryo: waveform analysis with photodiode array-based optical imaging.

Major difficulties investigating the developing cardiac conduction system stem from that the embryonic heart is extremely small (< 2 mm) and cardiac activation is relatively rapid (< 8 msec). The objective of this study was to investigate the electrophysiology of the embryonic chick cardiac conduction system at periseptation stages with a photodiode array-based detection method of optical mapping capable of high spatial and temporal resolution. Previous work indicated that, in chicken embryos, a switch occurs in ventricular activation pattern from immature base-to-apex to mature apex-to-base pattern at the time of ventricular septation. It was our aim to map activation in more detail to identify the active pathway or pathways of atrioventricular conduction at these particular stages. Analysis of preseptated hearts (n = 10) showed that the latest atrial activation took place just above the site of the earliest ventricular activation at the ventral left ventricular base. Analysis of postseptated hearts (n = 11) showed apex-to-base conduction consistent with activation through the maturing His-Purkinje system. Evaluation of hearts during septation revealed a gradual transition of ventricular activation patterns rather than an abrupt "switch." External pacing of preseptated hearts revealed significant slowing of interventricular conduction compared with spontaneous beats (spontaneous, 61.7 cm/sec +/- 9 cm/sec vs. paced, 36.5 cm/sec +/- 10 cm/sec). The more detailed mapping revealed that, before septation, the pattern of activation of the ventricular myocardium is consistent with direct atrial-ventricular myocardial connections at the left lateral atrioventricular junction; however, functional evidence for a preferential conduction pathway within the ventricles was present before septation.

Animals↗
PubMed1995

BOLD based functional MRI at 4 Tesla includes a capillary bed contribution: echo-planar imaging correlates with previous optical imaging using intrinsic signals.

We show that the EPI time course in functional MR imaging at 4 Tesla displays a multiphasic response in response to photic stimulation. Focal areas of gray matter display an initial negative change in signal intensity that reaches a maximum of 1% about 2 s after the onset of photic stimulation. This component then changes sign, reaching a positive maximum about 5 s after the onset of the stimulus. Other areas, including those where draining veins are visible, show only a positive signal change, reaching a maximum of about 6% after the onset of the visual stimulus. These time constants are in very good agreement with published data obtained with intrinsic optical mapping techniques, where a deoxygenation phase has been shown to occur in functionally specific cortical columns, followed by an increase in blood volume which is more distributed in nature. Thus, we believe there is strong evidence that a sensitivity to capillary oxygenation state is present in high S/N functional MR images obtained with EPI at 4 T.

Artifacts↗
PubMed2000

Modular bacterial artificial chromosome vectors for transfer of large inserts into mammalian cells.

To facilitate the use of large-insert bacterial clones for functional analysis, we have constructed new bacterial artificial chromosome vectors, pPAC4 and pBACe4. These vectors contain two genetic elements that enable stable maintenance of the clones in mammalian cells: (1) The Epstein-Barr virus replicon, oriP, is included to ensure stable episomal propagation of the large insert clones upon transfection into mammalian cells. (2) The blasticidin deaminase gene is placed in a eukaryotic expression cassette to enable selection for the desired mammalian clones by using the nucleoside antibiotic blasticidin. Sequences important to select for loxP-specific genome targeting in mammalian chromosomes are also present. In addition, we demonstrate that the attTn7 sequence present on the vectors permits specific addition of selected features to the library clones. Unique sites have also been included in the vector to enable linearization of the large-insert clones, e. g., for optical mapping studies. The pPAC4 vector has been used to generate libraries from the human, mouse, and rat genomes. We believe that clones from these libraries would serve as an important reagent in functional experiments, including the identification or validation of candidate disease genes, by transferring a particular clone containing the relevant wildtype gene into mutant cells or transgenic or knock-out animals.

Animals↗
PubMed2005

Properties of new, long-wavelength, voltage-sensitive dyes in the heart.

Membrane potential measurements using voltage-sensitive dyes (VSDs) have made important contributions to our understanding of electrophysiological properties of multi-cellular systems. Here, we report the development of long wavelength VSDs designed to record cardiac action potentials (APs) from deeper layers in the heart. The emission spectrum of styryl VSDs was red-shifted by incorporating a thienyl group in the polymethine bridge to lengthen and retain the rigidity of the chromophore. Seven dyes, Pittsburgh I to IV and VI to VIII (PGH I-VIII) were synthesized and characterized with respect to their spectral properties in organic solvents and heart muscles. PGH VSDs exhibited 2 absorption, 2 excitation and 2 voltage-sensitive emission peaks, with large Stokes shifts (> 100 nm). Hearts (rabbit, guinea pig and Rana pipiens) and neurohypophyses (CD-1 mice) were effectively stained by injecting a bolus (10-50 microl) of stock solution of VSD (2-5 mM) dissolved in in dimethylsulfoxide plus low molecular weight Pluronic (16% of L64). Other preparations were better stained with a bolus of VSD (2-5 mM) Tyrode's solution at pH 6.0. Action spectra measured with a fast CCD camera showed that PGH I exhibited an increase in fractional fluorescence, DeltaF/F = 17.5 % per AP at 720 nm with 550 nm excitation and DeltaF/F = - 6% per AP at 830 nm with 670 nm excitation. In frog hearts, PGH1 was stable with approximately 30% decrease in fluorescence and AP amplitude during 3 h of intermittent excitation or 1 h of continuous high intensity excitation (300 W Xe-Hg Arc lamp), which was attributed to a combination of dye wash out > photobleaching > dynamic damage > run down of the preparation. The long wavelengths, large Stokes shifts, high DeltaF/F and low baseline fluorescence make PGH dyes a valuable tool in optical mapping and for simultaneous mapping of APs and intracellular Ca(2+).

Aniline Compounds↗
PubMed2005

Fingerprinting of single viral genomes.

We demonstrate the use of technology developed for optical mapping to acquire DNA fingerprints from single genomes for the purpose of discrimination and identification of bacteria and viruses. Single genome fingerprinting (SGF) provides not only the size but also the order of the restriction fragments, which adds another dimension to the information that can be used for discrimination. Analysis of single organisms may eliminate the need to culture cells and thereby significantly reduce analysis time. In addition, samples containing mixtures of several organisms can be analyzed. For analysis, cells are embedded in an agarose matrix, lysed, and processed to yield intact DNA. The DNA is then deposited on a derivatized glass substrate. The elongated genome is digested with a restriction enzyme and stained with the intercalating dye YOYO-1. DNA is then quantitatively imaged with a fluorescence microscope and the fragments are sized to an accuracy >or=90% by their fluorescence intensity and contour length. Single genome fingerprints were obtained from pure samples of adenovirus, from bacteriophages lambda and T4 GT7, and from a mixture of the three viral genomes. SGF will enable the fingerprinting of uncultured and unamplified samples and allow rapid identification of microorganisms with applications in forensics, medicine, public health, and environmental microbiology.

Calibration↗
PubMed2006

Transchip: single-molecule detection of transcriptional elongation complexes.

A new single-molecule system, Transchip, was developed for analysis of transcription products at their genomic origins. The bacteriophage T7 RNA polymerase and its promoters were used in a model system, and resultant RNAs were imaged and detected at their positions along single template DNA molecules. The Transchip system has drawn from critical aspects of Optical Mapping, a single-molecule system that enables the construction of high-resolution ordered restriction maps of whole genomes from single DNA molecules. Through statistical analysis of hundreds of single-molecule template/transcript complexes, Transchip enables analysis of the locations and strength of promoters, the direction and processivity of transcription reactions, and the termination of transcription. These novel results suggest that the new system may serve as a high-throughput platform to investigate transcriptional events on a large genome-wide scale.

Bacteriophage T7↗
PubMed2006

Protective role of protein kinase C epsilon activation in ischemia-reperfusion arrhythmia.

PURPOSE: Ischemic heart disease carries an increased risk of malignant ventricular tachycardia (VT), fibrillation (VF), and sudden cardiac death. Protein kinase C (PKC) epsilon activation has been shown to improve the hemodynamics in hearts subjected to ischemia/reperfusion. However, very little is known about the role of epsilon PKC in reperfusion arrhythmias. Here we show that epsilon PKC activation is anti-arrhythmic and its inhibition is pro-arrhythmic. METHOD: Langendorff-perfused isolated hearts from epsilonPKC agonist (epsilonPKC activation), antagonist (epsilonPKC inhibition) transgenic (TG), and wild-type control mice were subjected to 30 min stabilization period, 10 min global ischemia, and 30 min reperfusion. Action potentials (APs) and calcium transients (CaiT) were recorded simultaneously at 37 degrees C using optical mapping techniques. The incidence of VT and VF was assessed during reperfusion. RESULTS: No VT/VF was seen in any group during the stabilization period in which hearts were perfused with Tyrode's solution. Upon reperfusion, 3 out of the 16 (19%) wild-type mice developed VT but no VF. In epsilonPKC antagonist group, in which epsilonPKC activity was downregulated, 10 out of 13 (76.9%) TG mice developed VT, of which six (46.2%) degenerated into sustained VF upon reperfusion. Interestingly, in epsilonPKC agonist mice, in which the activity of epsilonPKC was upregulated, no VF was observed and only 1 out of 12 mice showed only transient VT during reperfusion. During ischemia and reperfusion, CaiT decay was exceedingly slower in the antagonist mice compared to the other two groups. CONCLUSION: Moderate in vivo activation of epsilonPKC exerts beneficial antiarrhythmic effect vis-a-vis the lethal reperfusion arrhythmias. Abnormal CaiT decay may, in part, contribute to the high incidence of reperfusion arrhythmias in the antagonist mice. These findings have important implications for the development of PKC isozyme targeted therapeutics and subsequently for the treatment of ischemic heart diseases.

Action Potentials↗
PubMed2004

Effects of shock strengths on ventricular defibrillation failure.

BACKGROUND: The mechanism of defibrillation is controversial. Reentry appearing immediately after the shock has been shown to be responsible for defibrillation failure in some studies while other studies have demonstrated that a rapid train of focal activations with the first focus appearing >50 ms after the shock is responsible for failed defibrillation. We tested the hypothesis that both patterns can occur, but at different shock strengths. METHODS AND RESULTS: Biphasic 6/4 ms shocks of 100-900 V in 100-V increments were given after 10 s of ventricular fibrillation from electrodes in right ventricular apex and right atrium in five isolated pig hearts. Transmembrane activity was optically mapped from the anterior and posterior epicardium using two CCD cameras. The defibrillation threshold (DFT) was 786+/-199 V. The interval from the shock to the earliest post-shock activation was zero for shocks <400 V but increased with increasing shock voltage to 62+/-6 ms at 800 V. The number of post-shock phase singularities, which is related to reentry incidence, decreased continuously from pre-shock values for 100-V shocks to zero as the shock strength increased to 600 V. Focal activations were observed after shocks >600 V with no epicardial reentry present. CONCLUSION: Reentry is responsible for defibrillation failure for low-strength shocks. As the shock strength approaches the DFT, a focal epicardial activation pattern becomes responsible for failed defibrillation. Thus, the mechanism of defibrillation failure depends on shock strength, with focal activation as the mechanism for the clinically important near-DFT strength shocks.

Animals↗
PubMed2004

Prior ischemia enhances arrhythmogenicity in isolated canine ventricular wedge model of long QT 3.

OBJECTIVE: Ventricular tachyarrhythmias (VTs) occur frequently in patients having long QT syndrome (LQTS) or after acute myocardial ischemia. However, the synergistic effects of ischemia and LQTS on arrhythmia development are unclear. We evaluated the contribution of a prior episode of ischemia on the arrhythmogenicity of the LQTS. METHODS: Using a 256-channel optical mapping system, we mapped action potentials on the cut-exposed transmural surfaces of perfused and preconditioned muscle wedges isolated from canine left ventricular walls and recorded their transmural electrocardiogram (ECG). RESULTS: We observed that 40 min of global ischemia followed by 60 min of reperfusion, at which time action potential duration (APD) and conduction velocity had recovered, significantly enhanced the APD prolongation produced by 20 nmol/l anemone toxin II (ATX-II). Wedges after the above ischemia, reperfusion, and ATX-II procedures had 100% (8/8) occurrences of early afterdepolarizations (EADs) and 87.5% (7/8) occurrences of spontaneous VTs and reentry. We observed epicardial, midmyocardial, and endocardial occurrences of EADs in one, seven, and four wedges, respectively. Focal EADs and reentry were responsible for 73% and 18% of the repetitive activations in the VTs. In contrast, neither EADs nor VTs occurred in eight control wedges following identical procedures except without ischemia, and VT occurred in 20% wedges (2/10) after ischemia and reperfusion but before ATX-II. CONCLUSION: A prior episode of acute ischemia, even after apparent electrophysiologic recovery, enhances the arrhythmogenicity of LQTS induced by ATX-II through the development of EADs and reentry.

Action Potentials↗
PubMed2005

Effect of remodelling, stretch and ischaemia on ventricular fibrillation frequency and dynamics in a heart failure model.

OBJECTIVE: The dynamics of ventricular fibrillation (VF) in the presence of heart failure (HF) are different from those in the normal heart. This has been attributed solely to HF-induced electrophysiologic remodelling. We hypothesized that acute stretch and ischaemia, which are normally present during VF, might contribute significantly to the altered VF dynamics in HF. METHODS: HF was induced in eight sheep by rapid ventricular pacing for 4-6 weeks. Eight sheep served as controls. Optical mapping of isolated hearts was performed during VF at low intraventricular pressure (0-5 mm Hg), high pressure (25-30 mm Hg, in six HF and six controls), and at low pressure after 5 min of global ischaemia (six HF, five controls). Maximum dominant frequency (DF(max)), singularity point (SP) density and number of SP lasting more than one revolution (rotors) were analyzed. Possible statistical interactions between HF and ischaemia (HF x ischaemia) or stretch (HF x stretch) were evaluated. RESULTS: At low pressure, VF in HF was slower (13% reduction in DF(max)) and more organized than in control: 33% less SPs and 74% less rotors with 20% longer life spans. Acute stretch did not affect DF(max) but increased SP and rotors density similarly in both groups (no interaction HF x stretch). In controls, ischaemia caused a marked decrease in DF(max), SP density and incidence of rotors. However, in HF animals, the ischaemia-induced decrease in SP density was virtually abolished, indicating a significant interaction HF x ischaemia (p<0.005). CONCLUSIONS: HF remodelling decreases VF rate and increases VF organization. Acute stretch partially reverses these effects by a mechanism that is independent of remodelling. The effects of acute ischaemia on VF dynamics are significantly attenuated in HF compared to normal hearts.

Action Potentials↗
PubMed2005

Abnormal conduction and repolarization in late-activated myocardium of dyssynchronously contracting hearts.

BACKGROUND: Cardiac dyssynchrony due to intraventricular conduction delay produces heterogeneous regional wall stress and worsens arrhythmia susceptibility in failing hearts. We examined whether chronic dyssynchrony per se induces regionally heterogeneous electrophysiological remodeling. METHODS AND RESULTS: Adult dogs (n=9) underwent left bundle branch radiofrequency ablation (QRS duration increased from 50+/-7 to 104+/-7 ms); 6 untreated dogs served as controls. A subset of ablated (n=3) and control (n=4) dogs underwent tagged MR imaging to confirm ablation-induced left ventricular (LV) dyssynchrony. Four weeks later, hearts were excised and early (anterior)- and late (lateral)-activated myocardial segments were isolated. Conduction velocity (CV), action potential duration (APD), and refractory period (RP) of paced, arterially perfused myocardial wedges were studied by extracellular and optical mapping, and arrhythmia susceptibility was assessed by programmed stimulation. Regional stress-response kinase, calcium cycling, and gap junction protein expression were assayed by Western blotting, and the subcellular distribution of connexin43 was analyzed by immunofluorescence microscopy. CV, APD, and RP were significantly reduced in the late-activated, lateral wall of dyssynchronous hearts compared to the anterior wall. Normal differences in CV (endocardial>epicardial) were reversed in the dyssynchronous lateral LV. While the total expression of connexin43 was unaltered in dyssynchronous models, its subcellular location was redistributed in late-activated myocardium from intercalated discs to lateral myocyte membranes. Arrhythmias were rare in tissue from normal and dyssynchronous models. Total expression of calcium-cycling proteins (sarcoplasmic reticulum Ca2+-ATPase and phospholamban) and the stress-response kinase phospho-ERK did not vary regionally in either model. CONCLUSIONS: Dyssynchrony even in the absence of LV dysfunction induces regionally specific changes in conduction and repolarization. These changes support a novel mechanism linking mechanical dyssynchrony to persistent electrophysiological remodeling and heterogeneity.

Action Potentials↗
PubMed2005

Analysis of the electrophysiological properties and arrhythmias in directly contacted skeletal and cardiac muscle cell sheets.

OBJECTIVE: Autologous skeletal muscle cell (SM) transplantation into the in vivo heart sometimes induces serious arrhythmias. The purpose of this study was to investigate the electrophysiology of cardiomyocyte (CM) and SM in direct contact and to study the mechanism underlying the cause of arrhythmia using the recently developed cell sheet engineering technique. METHODS: Primary cultured rat neonatal SM and CM were prepared, and cell sheets were fabricated using temperature-responsive culture dishes. The action potential was recorded by a conventional microelectrode. Intracellular calcium concentration and optical mapping image of the action potential were recorded using Fluo-3 and di-4-ANEPPS, respectively. A video motion-detecting system was used for the detection of arrhythmias. RESULTS: SM myotubes occasionally displayed automaticity. SM sheets did not display synchronized contraction, but instead groups of myotubes contracted independently. The action potential of SM, induced by artificial pacing, did not expand to the entire sheet but was limited within a restricted, small area around the electrode, and it was unfeasible to generate an electrical connection or propagate an action potential between CM and SM sheets. SM sheets, in which some of the myotubes displayed automaticity, caused fibrillation-like contraction in the co-cultured CM sheets, and this arrhythmia was specifically blocked by the stretch-activated channel blocker GsMTx-4. CONCLUSIONS: These findings show that SM sheets do not contract synchronously or generate functional syncytia with the surrounding CM sheets and that stretch-induced arrhythmias due to spontaneous contraction of SM may occur in the CM sheet.

Action Potentials↗