Influence of Connexin Expression/Co-Expression Levels on Electrical Impulse Propagation Investigated in the HL-1 Cell Model

In the myocardium action potentials are transmitted from cell-to-cell through gap junctions. These specialised junctions play a pivotal role in regulating the speed and safety of impulse propagation by controlling the amount of depolarised current that is passed from excited to non-excited regions of the heart. In mammalian hearts gap junction proteins connexin43, connexin40 and connexin45 are co-expressed in distinctive combinations and relative quantities in functionally specialised subsets of cardiac myocyte. The functional consequences of these connexin expression/co-expression patterns in modulating impulse propagation are poorly understood. To study the relative importance of membrane excitability and electrical coupling in relation to propagation velocities, clones of the HL-1 mouse atrial myocyte tumour line were used as an in vitro cell model. Five clones were characterised for expression of myocytic markers, calcium handling proteins and connexins, two of which (#2 and #6) displayed large differences in conduction velocities using microelectrode arrays. To ascertain which factor(s) were the main determinants of speed of conduction, the membrane excitability (voltage-gated channels) and electrical coupling (gap junctions) between the two clones were compared. Sodium, L- and T-type calcium channels were present in both clones but no significant differences were found in the current densities. However, large differences were seen in expression levels of connexin43, connexin40 and connexin45. RNA interference combined with microelectrode arrays was employed to establish the relative importance of each connexin in impulse propagation. The results indicate that electrical coupling by gap junctions is a major determinant of conduction velocities in HL-1 cell lines. Further experiments using RNA interference to suppress the expression of proteins thought to play a role in the action potential parameters should help in defining the part played by either the active or passive electrical properties in action potential propagation

Effect of remote ischaemic conditioning on clinical outcomes in patients with acute myocardial infarction (CONDI-2/ERIC-PPCI): a single-blind randomised controlled trial.

BACKGROUND: Remote ischaemic conditioning with transient ischaemia and reperfusion applied to the arm has been shown to reduce myocardial infarct size in patients with ST-elevation myocardial infarction (STEMI) undergoing primary percutaneous coronary intervention (PPCI). We investigated whether remote ischaemic conditioning could reduce the incidence of cardiac death and hospitalisation for heart failure at 12 months. METHODS: We did an international investigator-initiated, prospective, single-blind, randomised controlled trial (CONDI-2/ERIC-PPCI) at 33 centres across the UK, Denmark, Spain, and Serbia. Patients (age >18 years) with suspected STEMI and who were eligible for PPCI were randomly allocated (1:1, stratified by centre with a permuted block method) to receive standard treatment (including a sham simulated remote ischaemic conditioning intervention at UK sites only) or remote ischaemic conditioning treatment (intermittent ischaemia and reperfusion applied to the arm through four cycles of 5-min inflation and 5-min deflation of an automated cuff device) before PPCI. Investigators responsible for data collection and outcome assessment were masked to treatment allocation. The primary combined endpoint was cardiac death or hospitalisation for heart failure at 12 months in the intention-to-treat population. This trial is registered with ClinicalTrials.gov (NCT02342522) and is completed. FINDINGS: Between Nov 6, 2013, and March 31, 2018, 5401 patients were randomly allocated to either the control group (n=2701) or the remote ischaemic conditioning group (n=2700). After exclusion of patients upon hospital arrival or loss to follow-up, 2569 patients in the control group and 2546 in the intervention group were included in the intention-to-treat analysis. At 12 months post-PPCI, the Kaplan-Meier-estimated frequencies of cardiac death or hospitalisation for heart failure (the primary endpoint) were 220 (8·6%) patients in the control group and 239 (9·4%) in the remote ischaemic conditioning group (hazard ratio 1·10 [95% CI 0·91-1·32], p=0·32 for intervention versus control). No important unexpected adverse events or side effects of remote ischaemic conditioning were observed. INTERPRETATION: Remote ischaemic conditioning does not improve clinical outcomes (cardiac death or hospitalisation for heart failure) at 12 months in patients with STEMI undergoing PPCI. FUNDING: British Heart Foundation, University College London Hospitals/University College London Biomedical Research Centre, Danish Innovation Foundation, Novo Nordisk Foundation, TrygFonden

Influence of connexin expression/co-expression levels on electrical impulse propagation investigated in the HL-1 cell model

In the myocardium action potentials are transmitted from cell-to-cell through gap junctions. These specialised junctions play a pivotal role in regulating the speed and safety of impulse propagation by controlling the amount of depolarised current that is passed from excited to non-excited regions of the heart. In mammalian hearts gap junction proteins connexin43, connexin40 and connexin45 are co-expressed in distinctive combinations and relative quantities in functionally specialised subsets of cardiac myocyte. The functional consequences of these connexin expression/co-expression patterns in modulating impulse propagation are poorly understood. To study the relative importance of membrane excitability and electrical coupling in relation to propagation velocities, clones of the HL-1 mouse atrial myocyte tumour line were used as an in vitro cell model. Five clones were characterised for expression of myocytic markers, calcium handling proteins and connexins, two of which (#2 and #6) displayed large differences in conduction velocities using microelectrode arrays. To ascertain which factor(s) were the main determinants of speed of conduction, the membrane excitability (voltage-gated channels) and electrical coupling (gap junctions) between the two clones were compared. Sodium, L- and T-type calcium channels were present in both clones but no significant differences were found in the current densities. However, large differences were seen in expression levels of connexin43, connexin40 and connexin45. RNA interference combined with microelectrode arrays was employed to establish the relative importance of each connexin in impulse propagation. The results indicate that electrical coupling by gap junctions is a major determinant of conduction velocities in HL-1 cell lines. Further experiments using RNA interference to suppress the expression of proteins thought to play a role in the action potential parameters should help in defining the part played by either the active or passive electrical properties in action potential propagation.EThOS - Electronic Theses Online ServiceNational Heart and Lung InstituteGBUnited Kingdo

Influence of exterior infill walls on the performance of RC frames under tsunami loads: Case study of school buildings in Sri Lanka

This paper assesses the structural performance of RC frame buildings subjected to tsunami-induced loads, accounting for the influence of exterior masonry infill walls on the overall structural performance. Both the in-plane and out-of-plane contributions of masonry infill walls are considered in the analysis. To illustrate the importance of accounting for exterior infill walls in the response of structures to tsunami, two case study buildings are considered and modelled in 3D. The first case study is a typical two-storey school building in Sri Lanka, and the second is a modified version of this design configuration proposed in Sri Lanka after the 2004 Indian Ocean Tsunami to provide more redundancy against scour. Through these case studies, the effect of the non-uniform distribution of infill walls in the building and their failure (or “breakaway”) on building performance is considered. The building performance is characterized by a number of response parameters (i.e., first yielding, development of two hinges, and shear failure in ground floor columns). The paper shows that the in-plane behaviour of exterior infill walls increases the flexural capacity and lateral stiffness of the structure, as would be expected. However, it also shows that an assumption of non-breakaway infill walls consistently leads to premature structural failure mechanisms, associated with the concentration of drag forces on seaward columns only. The results demonstrate that a good estimation of the location and occurrence of shear failure in structural elements can only be achieved by explicitly considering the out-of-plane behaviour and failure of exterior infill walls during an incremental tsunami load analysis. Finally, the Froude number assumed for the analysis is seen to strongly affect the performance of both structural and non-structural components, highlighting the importance of choosing realistic tsunami properties to perform a reliable capacity assessment

A new relative risk index for hospitals exposed to tsunami

The failure of hospitals in recent tsunami have caused extensive social and economiclosses. A simple but quantitative approach is required to assess the resilience of healthcaresystems to tsunami, which relates not only to hospital building integrity, but also tomaintaining hospital functionality. This paper proposes a new tsunami relative risk index(TRRI) that quantifies the impact of tsunami on critical units, (e.g. Intensive Care Unit,Maternity Ward, etc) in individual hospitals, as well as the impact on service provisionacross a network of hospitals. A survey form is specifically developed for collecting of fielddata on hospitals for the TRRI evaluation. In its current form TRRI is designed for hospitalbuildings of reinforced concrete construction, as these are the building types mostcommonly used worldwide for housing critical units. The TRRI is demonstratedthrough an application to three hospitals located along the southern coast of SriLanka. The TRRI is evaluated for three potential tsunami inundation events and isshown to be able to identify issues with both the building and functional aspects ofhospital critical units. Three “what-if” intervention scenarios are presented and their effecton the TRRI is assessed. Through this exercise, it is shown that the TRRI can be used bydecision makers to simply explore the effectiveness of individual and combinedinterventions in improving the tsunami resilience of healthcare provision across thehospital system

Northern blot analysis of total RNA extracted from the HL-1 clones (indicated on top of the picture).

<p>Membranes were hybridised with probes for NCX, L-type Ca²⁺ channel, T-type Ca²⁺ channel, RyR2 and SERCA2 as indicated on the left of the picture. Membranes were stained with ethidium bromide to visualize the ribosomal RNA bands 18S and 28S.</p

Ca²⁺ transient recordings from clones 2 and 6.

<p>(A) Spontaneous rhythmic oscillations of [Ca²⁺]_i in clones 2 and 6 after staining with fluo-4. (B) Both clones had a comparable [Ca²⁺]_i release but there was a significant prolongation in the time to peak, time to 50% decay and time to 90% decay in clone 2 compared with clone 6.</p

Northern blot analysis of total RNA extracted from the HL-1 clones (indicated on top of the picture).

<p>Membranes were hybridised with probes for NCX, L-type Ca²⁺ channel, T-type Ca²⁺ channel, RyR2 and SERCA2 as indicated on the left of the picture. Membranes were stained with ethidium bromide to visualize the ribosomal RNA bands 18S and 28S.</p