Load-dependent electrophysiological and structural cardiac remodelling studied in ultrathin myocardial slices.

Introduction: Myocardial slices are becoming an established system to study cardiac electrophysiology and pharmacological research and development. Unlike other preparations, cardiac slices are a multicellular preparation that has an intermediate, adequate complexity required for this research. Previous studies have successfully obtained slices from human biopsies and animal models, where the electrical and structural parameters could be maintained for several hours – a process which is comparable to other preparation types. Therefore, we aimed to use left ventricular myocardial slices obtained from rat models of mechanical unloading (HAHLT) and from two models of overload (TAC and SHR), to investigate electrophysiological and structural alterations in these models. Methods: Mechanical unloading was achieved by heterotopic abdominal heart and lung transplantation (HAHLT, 8 weeks) and overload was induced by thoracic aortic constriction (TAC, 10 and 20 weeks) in male Lewis rats. Spontaneous hypertensive rats (SHR) were also used as a second model of overload and were primarily induced by hypertension (3, 12 and 20 months). Brown Norway and Wistar Kyoto rats were used as the control groups for SHR. Myocardial slices from the left ventricle (LV) free wall were cut (300-350 µm thick) tangentially to the epicardial surface using a high-precision slow-advancing Vibratome and were point-stimulated using a multi-electrode array system (MEA), therefore, acquiring field potentials (FPs). Field potential duration (FPD) and conduction velocity (CV) were analysed locally and transmurally across the LV free wall. In addition, FPD heterogeneity within each slice was calculated. For the SHR group, the same slices used for the MEA recording were preserved and used subsequently to measure Cx43, Nav1.5 protein levels and fibrosis. Results: Slices obtained from normal rat hearts that are chronically unloaded were found to develop atrophy at a whole heart level. They showed an increase in FPD and its heterogeneity with preserved conduction properties when compared to controls. In TACs, an in vivo whole heart function assessment confirmed hypertrophy with no signs of cardiac dysfunction. Slices from TAC rats showed an increase in FPD at both 10 and 20 weeks after banding. FPD heterogeneity was increased at 10 weeks but normalised at 20 weeks. Changes in CV properties were observed in this group, showing a faster CV and longitudinal conduction velocity (CVL) at 10 weeks and no change at 20 weeks. Transverse conduction velocity (CVT) was unchanged in the TAC group. In SHRs, however, hypertrophy was confirmed and signs of dysfunction in the aged group (20 months) were observed due to the decrease in EF by 18%, especially when compared to the 12 months group. FPD and its heterogeneity was unchanged in SHR when compared to controls. Disease and age-related abnormalities in CV properties were observed in SHR and these were associated with changes in Cx43, Nav1.5 protein level and fibrosis. Conclusion: Myocardial slices are a suitable multicellular preparation to study electrophysiological remodelling obtained from different rat models of cardiovascular disease. In addition, it was possible to investigate the changes in CV and FPD transmurally in rats using this type of preparation method. Thus, this study supports the use of this multicellular preparation in understanding the mechanisms of cardiac disease and the testing of new treatments and therapeutic targets.Open Acces

Stress, Anxiety, and Depression in Pre-Clinical Medical Students: Prevalence and Association with Sleep Disorders

Our aim was to assess sleep quality in different subgroups of preclinical medical students, and then to identify specific lifestyle factors, academic and social factors as well as Corona virus related factors that were associated with poor sleeping quality and poor psychological health. Study participants were all medical students at King Saud University of Medical Sciences in the first and second years (648 students), and the study was conducted from December 2021 to January 2022. We administered the survey on paper as well as online. We used three types of questionnaires in this study. The first was a self-administered questionnaire, the second was a validated Insomnia Severity Index (ISI) for finding sleeping problems, and the third was a validated DASS 10 for determining Depression, Anxiety, and Stress. A total of 361 pre-clinical medical students consisted of 146 (40.4%) males and 215 (59.5%) females. The majority of the students, 246 (68.1%), were in their second year. Furthermore, in the current study, students who had poor academic performance (15.8%), satisfactory academic performance (21.3%), or good academic performance (30.7%) had significant sleeping problems found (χ2 = 19.4; p = 0.001), among them poor academic performance students 21.6%, satisfactory academic performance students (29.3%), and good academic performance students (29.3%) had moderate to severe levelled sleeping problems. Similarly, poor, satisfactory, and good academic performers experienced the highest levels of anxiety (poor = 21.5%; satisfactory = 22.1%; and good = 22.8%); stress (poor = 22.4%; satisfactory = 25.2%; and good = 22.4%); and depression (poor = 40.5%; satisfactory = 40.5%; and good = 11.9%). The majority of students (64.8%) reported that during the pandemic crisis their anxiety levels were high. Additionally, students reported significantly high sleeping issues (χ2 = 10.6; p = 0.001) and also serious psychological issues (Anxiety = 34.9 (0.000); Stress = 32.5 (0.000); and Depression = 5.42 (0.01)). There was a high prevalence of sleep issues, anxiety, stress, and depression among the pre-clinical medical students, with significantly higher sleeping disorders, anxiety, stress, and depression levels among those medical students who struggle with their academic performances, poor lifestyle factor, and poor Social and COVID management

Investigation of cardiac fibroblasts using myocardial slices

Aims: Cardiac fibroblasts (CFs) are considered the principal regulators of cardiac fibrosis. Factors that influence CF activity are difficult to determine. When isolated and cultured in vitro , CFs undergo rapid phenotypic changes including increased expression of \u3b1-SMA. Here we describe a new model to study CFs and their response to pharmacological and mechanical stimuli using in vitro cultured mouse, dog and human myocardial slices. Methods and Results: Unloading of myocardial slices induced CF proliferation without \u3b1-SMA expression up to 7 days in culture . CFs migrating onto the culture plastic support or cultured on glass expressed \u3b1SMA within 3 days. The cells on the slice remained \u3b1SMA(-) despite TGF-\u3b2 (20ng/mL) or angiotensin II (200\ub5M) stimulation. When diastolic load was applied to myocardial slices using A-shaped stretchers, CF proliferation was significantly prevented at day 3 and 7 (P\u2009<\u20090.001). Conclusions: Myocardial slices allow the study of CFs in a multicellular environment and may be used to effectively study mechanisms of cardiac fibrosis and potential target

Investigation of cardiac fibroblasts using myocardial slices

Aims: Cardiac fibroblasts (CFs) are considered the principal regulators of cardiac fibrosis. Factors that influence CF activity are difficult to determine. When isolated and cultured in vitro , CFs undergo rapid phenotypic changes including increased expression of α-SMA. Here we describe a new model to study CFs and their response to pharmacological and mechanical stimuli using in vitro cultured mouse, dog and human myocardial slices. Methods and Results: Unloading of myocardial slices induced CF proliferation without α-SMA expression up to 7 days in culture . CFs migrating onto the culture plastic support or cultured on glass expressed αSMA within 3 days. The cells on the slice remained αSMA(-) despite TGF-β (20ng/mL) or angiotensin II (200µM) stimulation. When diastolic load was applied to myocardial slices using A-shaped stretchers, CF proliferation was significantly prevented at day 3 and 7 (P < 0.001). Conclusions: Myocardial slices allow the study of CFs in a multicellular environment and may be used to effectively study mechanisms of cardiac fibrosis and potential target