Current understanding of ventricular action potential adaptation to physiological stress is generally based on protocols using non-physiological rates and conditions isolating rate effects from escalating adrenergic stimulation. To permit refined understanding, ventricular action potentials were assessed across physiological pacing frequencies in the presence and absence of adrenergic stimuli. Isolated and combined effects were analyzed to assess their ability to replicate in-vivo responses.Methods: Steady-state action potentials from ventricular myocytes isolated from male Wistar rats (3 months; N = 8 animals) were recorded at 37°C with steadystate pacing at 1, 2, 4, 6, 8 and 10 Hz using whole-cell patch-clamp. Action potential repolarization to 25, 50, 75, 90 and 100% of full repolarization (APD 25-100 ) was compared before and after 5 nM, 100 nM and 1 µM isoproterenol doses.Results: A Repeated measures ANOVA found APD 50-90 shortened with 5 nM isoproterenol infusion by 6-25% (but comparable across doses) (p ≤ 0.03). Pacing frequencies emulating a normal rat heart rate (6 Hz) prolonged APD 50 23% compared with 1 Hz pacing. Frequencies emulating exercise or stress (10 Hz) shortened APD 90 (29%). Conclusion:These results demonstrate modest action potential shortening in response to adrenergic stimulation and elevations in pacing beyond physiological resting rates. Our findings indicate changes in action potential plateau and late repolarization predominantly underlie simulated exercise responses in the rat heart. This work provides novel action potential reference data and will help model cardiac responses to physiological stimuli in the rat heart via computational techniques.

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Purpose The effect of eccentric (ECC) resistance exercise (RE) on myocardial mechanics is currently unknown. Method This study investigated ECC RE at varying intensities on left ventricular (LV) function using LV strain (ε), wall stress and haemodynamic parameters. Twenty-four healthy male volunteers completed ECC leg extensions at 20%, 50% and 80% of their ECC maximal voluntary contraction (MVC), whilst receiving echocardiograms. Global longitudinal ɛ, strain rate (SR), longitudinal tissue velocity, heart rate (HR), blood pressure (BP), mean arterial pressure (MAP), LV wall stress and rate pressure product (RPP) were assessed at baseline and during exercise. Results Left ventricular global ɛ, systolic SR and wall stress remained unchanged throughout. Systolic blood pressure (sBP), MAP and RPP increased at 80% and 50% intensities compared to rest (P < 0.01). Eccentric RE increased HR and peak late diastolic SR at all intensities compared to rest (P < 0.02). Conclusion The findings suggest acute ECC RE may not alter main parameters of LV function, supporting future potential for wider clinical use. However, future studies must investigate the impact of multiple repetitions and training on LV function.

To study the structural basis of pathological remodelling and altered calcium channel functional states in the heart, we sought to re-purpose high-affinity ligands of the cardiac calcium channel, the ryanodine receptor (RyR2), into super-resolution imaging probes. Imperacalcin (IpCa), a scorpion toxin peptide which induces channel sub-conduction states, and DPc10, a synthetic peptide corresponding to a sequence of the RyR2, which replicates arrhythmogenic CPVT functional changes, were used in fluorescent imaging experiments. Isolated adult rat ventricular cardiomyocytes were saponin-permeabilised and incubated with each peptide. IpCa-A546 became sequestered into the mitochondria. This was prevented by treatment of the permeabilised cells with the ionophore FCCP, revealing a striated staining pattern in confocal imaging which had weak colocalisation with RyR2 clusters. Poor specificity (as an RyR2 imaging probe) was confirmed at higher resolution with expansion microscopy (proExM) (~70 nm). DPc10-FITC labelled a striated pattern, which had moderate colocalisation with RyR2 cluster labelling in confocal and proExM. There was also widespread non-target labelling of the Z-discs, intercalated discs, and nuclei, which was unaffected by incubation times or 10 mM caffeine. The inactive peptide mut-DPc10-FITC (which causes no functional effects) displayed a similar labelling pattern. Significant labelling of structures unrelated to RyR2 by both peptide conjugates makes their use as highly specific imaging probes of RyR2 in living isolated cardiomyocytes highly challenging. We investigated the native DPc10 sequence within the RyR2 structure to understand the domain interactions and proposed mechanism of peptide binding. The native DPc10 sequence does not directly interact with another domain, and but is downstream of one such domain interface. The rabbit Arg2475 (equivalent to human Arg2474, mutated in CPVT) in the native sequence is the most accessible portion and most likely location for peptide disturbance, suggesting FITC placement does not impact peptide binding.

This study aimed to simulate ventricular responses to elevations in myocyte pacing and adrenergic stimulation using a novel electrophysiological rat model and investigate ion channel responses underlying action potential (AP) modulations.Peak ion currents and AP repolarization to 50% and 90% of full repolarization (APD 50-90 ) were recorded during simulations at 1-10 Hz pacing under control

Diseases of the cardiovascular system have been the biggest cause of mortality for the majority of the last century, currently contributing to almost a third of deaths every year globally. Ageing associates with changes to the structure and function of the heart and vascular system that progressively increase the incidence of abnormalities, morbidity, and cardiovascular disease. The burden of ageing and its relationship to cardiovascular disease risk highlights the need for more research into the underlying mechanisms involved and how they may be treated and/or prevented. Factors influencing adrenergic dysfunction may explain a significant part of the age-related deterioration in health and responsiveness of the cardiovascular system. Increased sympathetic activity in old age overstimulates adrenergic receptors and causes detrimental changes within the associated signalling mechanisms including a reduction in receptor number and downstream effector efficiency. Pharmacological agents such as metformin, resveratrol, beta-blockers, and angiotensin converting enzyme (ACE) inhibitors have been identified as potential anti-ageing therapies with cardiovascular effects, which may be beneficial in treating the decline in cardiovascular function with old age. Regular exercise has also shown promise in the prevention and treatment of harmful age-related effects on the cardiovascular system. This review will investigate age-associated vascular and cardiac remodelling, and the link between adrenergic dysfunction and vascular and cardiac control. This review will also consider whether pharmacological or non-pharmacological therapies are most effective, or indeed complimentary to potentially optimise ageing of the cardiovascular system and improve quality of life in the elderly.