A common co-morbidity modulates disease expression and treatment efficacy in inherited cardiac sodium channelopathy.

Aims: Management of patients with inherited cardiac ion channelopathy is hindered by variability in disease severity and sudden cardiac death (SCD) risk. Here, we investigated the modulatory role of hypertrophy on arrhythmia and SCD risk in sodium channelopathy. Methods and results: Follow-up data was collected from 164 individuals positive for the SCN5A-1795insD founder mutation and 247 mutation-negative relatives. A total of 38 (obligate) mutation-positive patients died suddenly or suffered life-threatening ventricular arrhythmia. Of these, 18 were aged >40 years, a high proportion of which had a clinical diagnosis of hypertension and/or cardiac hypertrophy. While pacemaker implantation was highly protective in preventing bradycardia-related SCD in young mutation-positive patients, seven of them aged >40 experienced life-threatening arrhythmic events despite pacemaker treatment. Of these, six had a diagnosis of hypertension/hypertrophy, pointing to a modulatory role of this co-morbidity. Induction of hypertrophy in adult mice carrying the homologous mutation (Scn5a1798insD/+) caused SCD and excessive conduction disturbances, confirming a modulatory effect of hypertrophy in the setting of the mutation. The deleterious effects of the interaction between hypertrophy and the mutation were prevented by genetically impairing the pro-hypertrophic response and by pharmacological inhibition of the enhanced late sodium current associated with the mutation. Conclusion: This study provides the first evidence for a modulatory effect of co-existing cardiac hypertrophy on arrhythmia risk and treatment efficacy in inherited sodium channelopathy. Our findings emphasize the need for continued assessment and rigorous treatment of this co-morbidity in SCN5A mutation-positive individuals.

Plakophilin-2 Haploinsufficiency Causes Calcium Handling Deficits and Modulates the Cardiac Response Towards Stress.

Human variants in plakophilin-2 (PKP2) associate with most cases of familial arrhythmogenic cardiomyopathy (ACM). Recent studies show that PKP2 not only maintains intercellular coupling, but also regulates transcription of genes involved in Ca2+ cycling and cardiac rhythm. ACM penetrance is low and it remains uncertain, which genetic and environmental modifiers are crucial for developing the cardiomyopathy. In this study, heterozygous PKP2 knock-out mice (PKP2-Hz) were used to investigate the influence of exercise, pressure overload, and inflammation on a PKP2-related disease progression. In PKP2-Hz mice, protein levels of Ca2+-handling proteins were reduced compared to wildtype (WT). PKP2-Hz hearts exposed to voluntary exercise training showed right ventricular lateral connexin43 expression, right ventricular conduction slowing, and a higher susceptibility towards arrhythmias. Pressure overload increased levels of fibrosis in PKP2-Hz hearts, without affecting the susceptibility towards arrhythmias. Experimental autoimmune myocarditis caused more severe subepicardial fibrosis, cell death, and inflammatory infiltrates in PKP2-Hz hearts than in WT. To conclude, PKP2 haploinsufficiency in the murine heart modulates the cardiac response to environmental modifiers via different mechanisms. Exercise upon PKP2 deficiency induces a pro-arrhythmic cardiac remodeling, likely based on impaired Ca2+ cycling and electrical conduction, versus structural remodeling. Pathophysiological stimuli mainly exaggerate the fibrotic and inflammatory response.

Students generate items for an online formative assessment: Is it motivating?

BACKGROUND: A reported problem with e-learning is sustaining students' motivation. We propose a framework explaining to what extent an e-learning task is motivating. This framework includes students' perceived Value of the task, Competence in executing the task, Autonomy over how to carry out the task, and Relatedness. METHODS: To test this framework, students generated items in an online environment and answered questions developed by their fellow students. Motivation was measured by analyzing engagement with the task, with an open-ended questionnaire about engagement, and with the motivated strategies for learning questionnaire (MSLQ). RESULTS: Students developed 59 questions and answered 1776 times on the questions. Differences between students who did or did not engage in the task are explained by the degree of self-regulation, time management, and effort regulation students report. There was a significant relationship between student engagement and achievement after controlling for previous academic achievement. CONCLUSIONS: This study proposes a way of explaining the motivational value of an e-learning task by looking at students' perceived competence, autonomy, value of the task, and relatedness. Student-generated items are considered of high task value, and help to perceive relatedness between students. With the right instruction, students feel competent to engage in the task.

Peer-instructed seminar attendance is associated with improved preparation, deeper learning and higher exam scores: a survey study.

BACKGROUND: Active engagement in education improves learning outcomes. To enhance active participation in seminars, a student-centered course design was implemented and evaluated in terms of self-reported preparation, student motivation and exam scores. We hypothesized that small group learning with intensive peer interaction, using buzz-groups followed by plenary discussion, would motivate students to prepare seminar assignments at home and to actively engage in the seminars. Active engagement involved discussion of the preparatory assignments until consensus was reached. METHODS: In total seven seminars were scheduled in a 10-week physiology course of an undergraduate Biomedical Sciences program. After each seminar, students were asked to fill out their perceptions of preparation and quality of the seminar (deepening of knowledge and confidence in answers) on a five-point scale using electronic questionnaires. Student motives were first collected using open questions. In the final questionnaire students were asked to indicate on a five-point scale how each motive was perceived. Students overall explanations why they had learned from seminars were collected via open questions in the final questionnaire. One hundred and twenty-four students of the cohort from November 2012 to February 2013 (82.6 %) voluntarily participated. Students' motives to prepare and attend seminars were analyzed by inspection of descriptive statistics. Linear regression analysis was conducted to relate student preparation to the quality of seminars, seminar attendance to exam scores, and exam scores to the quality of seminars. Answers to open questions were deductively clustered. RESULTS: Studying the material, training for exams and comparing answers with peers motivated students to prepare the seminars. Students were motivated to participate actively because they wanted to keep track of correct answers themselves, to better understand the content and to be able to present their findings in plenary discussions. Perceived preparation of peers was positively associated with the perceived quality of seminars. Also, seminar attendance was positively associated with exam scores. Students' overall explanations suggest that discussing with peers and applying knowledge in pathophysiology cases underlies this association. CONCLUSION: Discussion with well-prepared peers during seminars improves student perceptions of deeper learning and peer-instructed seminar attendance was associated with higher exam scores.

CTGF knockout does not affect cardiac hypertrophy and fibrosis formation upon chronic pressure overload.

BACKGROUND: One of the main contributors to maladaptive cardiac remodeling is fibrosis. Connective tissue growth factor (CTGF), a matricellular protein that is secreted into the cardiac extracellular matrix by both cardiomyocytes and fibroblasts, is often associated with development of fibrosis. However, recent studies have questioned the role of CTGF as a pro-fibrotic factor. Therefore, we aimed to investigate the effect of CTGF on cardiac fibrosis, and on functional, structural, and electrophysiological parameters in a mouse model of CTGF knockout (KO) and chronic pressure overload. METHODS AND RESULTS: A new mouse model of global conditional CTGF KO induced by tamoxifen-driven deletion of CTGF, was subjected to 16weeks of chronic pressure overload via transverse aortic constriction (TAC, control was sham surgery). CTGF KO TAC mice presented with hypertrophic hearts, and echocardiography revealed a decrease in contractility on a similar level as control TAC mice. Ex vivo epicardial mapping showed a low incidence of pacing-induced ventricular arrhythmias (2/12 in control TAC vs. 0/10 in CTGF KO TAC, n.s.) and a tendency towards recovery of the longitudinal conduction velocity of CTGF KO TAC hearts. Picrosirius Red staining on these hearts unveiled increased fibrosis at a similar level as control TAC hearts. Furthermore, genes related to fibrogenesis were also similarly upregulated in both TAC groups. Histological analysis revealed an increase in fibronectin and vimentin protein expression, a significant reduction in connexin43 (Cx43) protein expression, and no difference in NaV1.5 expression of CTGF KO ventricles as compared with sham treated animals. CONCLUSION: Conditional CTGF inhibition failed to prevent TAC-induced cardiac fibrosis and hypertrophy. Additionally, no large differences were found in other parameters between CTGF KO and control TAC mice. With no profound effect of CTGF on fibrosis formation, other factors or pathways are likely responsible for fibrosis development.

Ex vivo and in vivo administration of fluorescent CNA35 specifically marks cardiac fibrosis.

Cardiac fibrosis is a major hallmark of cardiac diseases. For evaluation of cardiac fibrosis, the development of highly specific and preferably noninvasive methods is desired. Our aim was to evaluate CNA35, a protein known to specifically bind to collagen, as a specific marker of cardiac fibrosis. Fluorescently labeled CNA35 was applied ex vivo on tissue sections of fibrotic rat, mouse, and canine myocardium. After quantification of CNA35, sections were examined with picrosirius red (PSR) and compared to CNA35. Furthermore, fluorescently labeled CNA35 was administered in vivo in mice. Hearts were isolated, and CNA35 labeling was examined in tissue sections. Serial sections were histologically examined with PSR. Ex vivo application of CNA35 showed specific binding to collagen and a high correlation with PSR (Pearson r  =  .86 for mice/rats and r  =  .98 for canine; both p < .001). After in vivo administration, CNA35 labeling was observed around individual cardiomyocytes, indicating its ability to penetrate cardiac endothelium. High correlation was observed between CNA35 and PSR (r  =  .91, p < .001). CNA35 specifically binds to cardiac collagen and can cross the endothelial barrier. Therefore, labeled CNA35 is useful to specifically detect collagen both ex vivo and in vivo and potentially can be converted to a noninvasive method to detect cardiac fibrosis.

Functional consequences of abnormal Cx43 expression in the heart.

The major gap junction protein expressed in the heart, connexin43 (Cx43), is highly remodeled in the diseased heart. Usually, Cx43 is down-regulated and heterogeneously redistributed to the lateral sides of cardiomyocytes. Reverse remodeling of the impaired Cx43 expression could restore normal cardiac function and normalize electrical stability. In this review, the reduced and heterogeneous Cx43 expression in the heart will be addressed in hypertrophic, dilated and ischemic cardiomyopathy together with its functional consequences of conduction velocity slowing, dispersed impulse conduction, its interaction with fibrosis and propensity to generate arrhythmias. Finally, different therapies are discussed. Treatments aimed to improve the Cx43 expression levels show new potentially anti-arrhythmic therapies during heart failure, but those in the context of acute ischemia can be anti-arrhythmogenic at the cost of larger infarct sizes. This article is part of a Special Issue entitled: The Communicating junctions, composition, structure and characteristics.

Students' motives for using online formative assessments when preparing for summative assessments.

BACKGROUND: Formative assessments intend to provide feedback on student performance in order to improve and accelerate learning. Several studies have indicated that students using online formative assessments (OFAs), have better results on their exams. AIMS: The present study aims to provide insight in student reasons for using or not using available OFAs. METHOD: Three OFAs with feedback were available in a second year undergraduate course in physiology for biomedical sciences students (N = 147). First, students received an open questionnaire about why they did (not) complete the first two OFAs. Based on this data, a closed questionnaire was developed and distributed among students. Exploratory factor analysis (EFA) was applied. RESULTS: The results indicate reasons why students do (not) use the OFAs. The EFA for using the OFAs indicated three factors, that were interpreted as collecting (1) feed up, (2) feed forward, and (3) feed back information. The main reasons for not using the OFAs were lack of time and having completed the questions before. CONCLUSIONS: Students' reasons for using OFAs can be described in terms of collecting feed up, forward and back information and students' reasons for not using OFAs can be student-, teacher-, or mode-related.

Online formative tests linked to microlectures improving academic achievement.

BACKGROUND: Online formative tests (OFTs) are powerful tools to direct student learning behavior, especially when enriched with specific feedback. AIM: In the present study, we have investigated the effect of OFTs enriched with hyperlinks to microlectures on examination scores. METHODS: OFTs, available one week preceding each midterm and the final exams, could be used voluntarily. The use of OFTs was related to scores on midterm and final exams using ANOVA, with prior academic achievement as a covariate. RESULTS: On average, 74% of all students used the online formative tests (OFT+) while preparing for the summative midterm exam. OFT+ students obtained significantly higher grades compared to OFT-students, both without and with correction for previous academic achievement. Two out of three final exam scores did not significantly improve. CONCLUSION: Students using online formative tests linked to microlectures receive higher grades especially in highly aligned summative tests.

One size does not fit all: an exploratory interview study on how translational researchers navigate the current academic reward system.

Introduction: Translational research is a subfield of the biomedical life sciences that focuses on clinically driven healthcare innovations. The workforce of this subfield, i.e., translational researchers, are diversely specialized and collaborate with a multitude of stakeholders from diverse disciplines in and outside academia in order to navigate the complex path of translating unmet clinical needs into research questions and ultimately into advancements for patient care. Translational researchers have varying responsibilities in the clinical, educational, and research domains requiring them to split their time two- or three-ways. Working between these domains and alongside peers who do not split their time as such, raises questions about the academic reward system used to recognize their performance, which mainly focuses on publication metrics within the research domain. What is unclear is how combining research tasks with tasks in the clinical and/or educational domains effects translational researchers and how they navigate the academic reward system. Methods: In this exploratory interview study, semi-structured interviews were conducted to gain a deeper understanding of the current academic reward system for translational researchers. Stratified purposeful sampling was used to recruit 14 translational researchers from varying countries, subspecialties, and career stages. The interviews were coded after data collection was complete and arranged into three overarching result categories: intrinsic motivation, extrinsic factors, and ideal academic reward system and advice. Results: We found that these 14 translational researchers were intrinsically motivated to achieve their translational goals while working in settings where clinical work was reported to take priority over teaching which in turn took priority over time for research. However, it is the latter that was explained to be essential in the academic reward system which currently measures scientific impact largely based on publications metrics. Conclusion: In this study, translational researchers were asked about their thoughts regarding the current academic reward system. Participants shared possible structural improvements and ideas for specialized support on an individual, institutional, and also international level. Their recommendations focused on acknowledging all aspects of their work and led to the conclusion that traditional quantitative academic reward metrics do not fully align with their translational goals.

Reduced connexin40 protein expression in the right atrial appendage of patients bearing the minor connexin40 allele (-44 G --> A).

AIMS: The occurrence of connexin40 (Cx40) minor polymorphism (-44 G → A) was increased in patients with idiopathic atrial fibrillation (AF), although its effect on atrial Cx40 protein expression is unknown. We aimed to evaluate whether alterations in Cx40 are directly linked to the development of AF, we studied the effect of this polymorphism on Cx40 expression and distribution in patients without any history of AF and in patients who developed post-operative AF. METHODS AND RESULTS: Hundred and eight patients (mean age 67 ± 9 years), without a history of AF or conditions that predispose to AF, were included. During heart surgery, 10 cc blood was collected for DNA genotyping and the right atrial appendage was partly excised. Ten patients (9%) were homozygous for the minor allele (AA, Group 1), 30 (28%) were heterozygous (AG, Group 2), and 68 (63%) were non-carriers (GG, Group 3). Ten age- and sex-matched tissue samples per group were analysed for Cx40 expression by: (i) real-time quantitative polymerase chain reaction (Q-PCR), (ii) western blotting, and (iii) immunohistochemistry on cryosections. Real-time quantitative polymerase chain reaction showed no significant differences of Cx40 mRNA among the groups. Western blot analysis, however, revealed a reduction in Cx40 protein in Groups 1 (-36.4%) and 2 (-39.5%) as compared with Group 3. Immunohistochemistry confirmed this reduction but indicated an unaltered subcellular distribution of the remaining Cx40. Incidence of post-operative AF (28%) was age-dependent but unrelated to the presence of the polymorphism or fibrosis. CONCLUSION: Presence of the Cx40 minor allele (-44 G → A) results in a uniform down-regulation of right atrial appendage Cx40 protein which was not significantly related to development of post-operative AF.

Direct detection of myocardial fibrosis by MRI.

Excessive collagen deposition is a major hallmark of cardiac disease. Fibrosis reduces cardiac function and plays a major role in cardiac arrhythmogeneity. Despite the clinical importance, there is no non-invasive technique for direct detection of myocardial fibrosis yet. Ultra short echo time (UTE) MRI has been shown to detect tissues with a fast T(2)* signal decay. Collagen has a fast T(2)* signal decay compared to myocardium and should therefore be detectable with UTE MRI. This study aims to investigate the use of UTE MRI to detect fibrosis after myocardial infarction without using exogenous contrast. In 7 male Lewis rats either myocardial infarction was created (n=5) or sham surgery was performed (n=2). Six weeks after surgery, hearts were isolated and visualized by MRI. Images were acquired with UTE (TE 0.15ms), to detect tissue with a fast T(2)* decay. Acquired conventional images (TE=6.0ms) were subtracted from UTE images to maintain only 'short living signal' (SLS): tissue with a fast decay. In infarcted hearts, SLS was observed in subtracted images, whereas in control hearts hardly any SLS was detected. Subtracted images were cross-referenced with histology and showed that the SLS area observed with UTE MRI corresponded to the collagen-rich areas observed in histology. Normalized SLS areas correlated well with the normalized collagen-rich areas; r=0.7, p=0.002. We show for the first time that UTE MRI technology can be used for direct detection of post-infarcted fibrosis without the use of contrast agents.

Fibrosis and cardiac arrhythmias.

In this review article about fibrosis and arrhythmias, we show that the amount of collagen, a normal element of the heart muscle, increases with age and in heart disease. The relation between fibrosis and electrophysiological parameters such as conduction, fractionation of electrograms, abnormal impulse initiation as well as arrhythmogenicity is discussed. Next to the amount of fibrosis, we offer data suggesting that collagen texture too plays a role in conduction slowing and arrhythmia vulnerability. Data are shown revealing that fibrosis can also be induced by reduced sodium channel and connexin43 expression. Finally contrast-enhanced magnetic resonance to detect fibrosis and ventricular tachycardia vulnerability in a noninvasive way as well as a reduction of fibrosis and arrhythmogenicity by inhibition of the renin-angiotensin-aldosterone system is discussed.

Biomarkers of myocardial fibrosis.

Increased cardiac collagen deposition is observed in almost every cardiac disease and plays an important role in the deteriorating function of the diseased heart. Propeptides of procollagen types I and III, the 2 major collagen types in the heart, can be detected in circulation. Although these propeptides reflect collagen synthesis, also breakdown products of collagen and the matrix metalloproteinases, responsible for the breakdown of the extracellular matrix, can be detected in blood and are used for investigating the turnover of collagen. Clinical trials are performed in recent years to examine the usage of these biomarkers in a diagnostic or prognostic way in heart failure patients. This review aims to discuss the formation of fibrosis, and studies investigating these biomarkers in heart failure are reviewed in this article. In addition, it is conferred what the flaws are of translating these biomarker levels to cardiac fibrosis formation and where we stand in using these biomarkers in clinics.

Cardiac connexins and impulse propagation.

Gap junctions form the intercellular pathway for cell-to-cell transmission of the cardiac impulse from its site of origin, the sinoatrial node, along the atria, the atrioventricular conduction system to the ventricular myocardium. The component parts of gap junctions are proteins called connexins (Cx), of which three main isoforms are found in the conductive and working myocardial cells: Cx40, Cx43, and Cx45. These isoforms are regionally expressed in the heart, which suggests a specific role or function of a specific connexin in a certain part of the heart. Using genetically modified mice, the function of these connexins in the different parts of the heart have been assessed in the past years. This review will follow the cardiac impulse on its path through the heart and recapitulate the role of the different connexins in the different cardiac compartments.

Reduction of fibrosis-related arrhythmias by chronic renin-angiotensin-aldosterone system inhibitors in an aged mouse model.

Myocardial fibrosis increases arrhythmia vulnerability of the diseased heart. The renin-angiotensin-aldosterone system (RAAS) governs myocardial collagen synthesis. We hypothesized that reducing cardiac fibrosis by chronic RAAS inhibition would result in reduced arrhythmia vulnerability of the senescent mouse heart. Wild-type mice (52 wk old) were treated for 36 wk: 1) untreated control (C); 2) eplerenone (E); 3) losartan (L); and 4) cotreatment with eplerenone and losartan (EL). Ventricular epicardial activation mapping was performed on Langendorff-perfused hearts. Arrhythmia inducibility was tested by one to three premature stimuli and burst pacing. Longitudinal and transverse conduction velocity and dispersion of conduction were determined during pacing at a basic cycle length of 150 ms. Sirius red staining (collagen) was performed. As a result, in the RV of mice in the E, L, and EL groups, transverse conduction velocity was significantly increased and anisotropic ratio was significantly decreased compared with those values of mice in the C group. Anisotropic reentrant arrhythmias were induced in 52% of untreated mice and significantly reduced to 22%, 26%, and 16% in the E, L, and EL groups, respectively. Interstitial fibrosis was significantly decreased in both the RV and LV of all treated groups. Scattered patches of replacement fibrosis were found in 90% of untreated hearts, which were significantly reduced in the E, L, and EL groups. A strong correlation between the abundance of patchy fibrosis and arrhythmia inducibility was found. In conclusion, chronic RAAS inhibition limited aging-related interstitial fibrosis. The lower arrhythmogeneity of treated mice was directly correlated to the reduced amount of patchy fibrosis.

High-rate pacing reduces variability of repolarization and prevents repolarization-dependent arrhythmias in dogs with chronic AV block.

INTRODUCTION: high-rate pacing may have an inhibitory effect on the initiation of Torsade de Pointes arrhythmias (TdP). However, permanent pacing is only indicated in high-risk patients. We performed a proof of concept study into automatic overdrive pacing for prevention of drug-induced TdP, using short-term variability of repolarization (STV) as a feedback parameter of arrhythmic risk. METHODS AND RESULTS: the minimal signal sampling frequency required for measuring STV was determined through computer simulation. Arrhythmogenic response to dofetilide (25 microg/kg/5 minutes) was tested at two different paced heart rates (60-65 bpm vs 100-110 bpm) in 7 dogs with chronic atrioventricular block, while recording right and left ventricular (LV) monophasic action potential (MAP) and LV electrogram (EGM). Simulations showed a sampling frequency of 500 Hz is sufficient to capture relevant STV values. High-rate pacing prevented dofetilide-induced TdP seen at the low rate (low: 6/7 vs high: 1/7). At the low rate, STV from LV MAP duration increased before occurrence of spontaneous, ectopic activity and TdP (1.7 ± 0.6-3.0 ± 1.8 ms, P < 0.05), but at the high-rate STV did not change significantly (0.9 ± 0.2-1.5 ± 1.4 ms, NS). Regression analysis showed a close relation between STV calculated from LV MAP and from LV EGM (R(2) = 0.71). CONCLUSIONS: high-rate pacing increases repolarization reserve in dogs with chronic atrioventricular block, preventing dofetilide-induced TdP. Changes in repolarization reserve are reflected in values of STV.

Differences in the pattern of ventricular activation in small rodents determined by morphological organization of the cardiac ventricular conduction system.

Ventricular activation of the mouse heart differs significantly compared to activation in larger mammals. Knowledge of structural and functional characteristics of laboratory animals is essential for evaluation of results obtained from experiments. The present study was performed to evaluate whether the different pattern of activation is common to small rodents or unique for mice. Hearts of adult Wistar rats were isolated and Langendorff perfused. After removing the right and left ventricular free wall, extracellular activity of the septum and bundle branches (BB) was determined using a multi-terminal electrode harboring 247 terminals. Immunolabeling on cryosections was performed to assess expression and distribution of the gap junction proteins Connexin40 (Cx40), Cx43, Cx45, contractile (Desmin, alpha-actinin) and intercalated disk-related (N-cadherin, beta-catenin) proteins. Collagen distribution was assessed by Sirius Red staining. Reconstruction of the left and right bundle branch (LBB and RBB) using immuno-labeling revealed that the LBB spreads all over the septal surface. The RBB too is broad, albeit to a lesser extend than LBB. A sheet of connective tissue electrically separates the common bundle and proximal BB from the septal working myocardium. Immunolabeling revealed clear differences between the conduction system and the working myocardium with respect to expression level and distribution of the different proteins analyzed. The morphological organization of the area resulted in an electrical activation pattern of the septum comparable to what is common in larger mammals: earliest activation at the midseptum via the bundle branches. From our data we conclude that the pattern of ventricular activation in the rat heart and the structure of the conduction system fit to data described for larger mammals and differ from the different pattern previously found in mouse heart.

Cardiac cell-cell junctions in health and disease: Electrical versus mechanical coupling.

Intercalated discs are the membrane sites where individual cardiomyocytes are connected to each other. Adherens-, desmosomal-, and gap junctions are situated in the intercalated disc and ensure mechanical coupling between cells and enable propagation of electrical impulses throughout the heart. A number of cardiac disorders, for example arrhythmogenic right ventricular dysplasia/cardiomyopathy, have been described in which an impaired mechanical coupling leads to electrical dysfunction, with occurrence of fatal arrhythmias. In this article the interaction between electrical and mechanical coupling is explored by reviewing studies performed in patients, animals, and in vitro. In these studies the effect of changes in protein composition of a mechanical junction on the electrical junction, and vice versa were investigated. It is shown that impaired electrical coupling does not change mechanical coupling. However, impaired mechanical coupling largely affects electrical coupling.