Muscarinic Receptor Activation Reduces Force and Arrhythmias in Human Atria Independent of IK,ACh.

ABSTRACT: In human hearts, muscarinic receptors (M-R) are expressed in ventricular and atrial tissue, but the acetylcholine-activated potassium current (IK,ACh) is expressed mainly in the atrium. M-R activation decreases force and increases electrical stability in human atrium, but the impact of IK,ACh to both effects remains unclear. We used a new selective blocker of IK,ACh to elaborate the contribution of IK,ACh to M-R activation-mediated effects in human atrium. Force and action potentials were measured in rat atria and in human right atrial trabeculae. Cumulative concentration-effect curves for norepinephrine-induced force and arrhythmias were measured in the presence of carbachol (CCh; 1 µM) or CCh together with the IK,ACh -blocker XAF-1407 (1 µM) or in time-matched controls. To investigate the vulnerability to arrhythmias, we performed some experiments also in the presence of cilostamide (0.3 µM) and rolipram (1 µM), inhibiting PDE3 and PDE4. In rat atria and human right atrial trabeculae, CCh shortened the action potential duration persistently. However, the direct negative inotropy of CCh was only transient in human, but stable in rat atria. In rat and human atria, the negative inotropic effect was insensitive to blockage of IK,ACh by XAF-1407. In the presence of cilostamide and rolipram about 40% of trabeculae developed arrhythmias when exposed to norepinephrine. CCh prevented these concentration-dependent norepinephrine-induced arrhythmias, again insensitive to XAF-1407. Maximum catecholamine-induced force was not depressed by CCh. In human atrium, the direct and the indirect negative inotropic effect of CCh are independent of IK,ACh. The same applies to the CCh-mediated suppression of norepinephrine/PDE-inhibition-induced arrhythmias.

Effectiveness of a multidisciplinary and transitional nutritional intervention compared with standard care on health-related quality of life among acutely admitted medical patients aged ≥65 years with malnutrition or risk of malnutrition: A randomized controlled trial.

BACKGROUND & AIM: Malnutrition, risk of malnutrition, and risk factors for malnutrition are prevalent among acutely admitted medical patients aged ≥65 years and have significant health-related consequences. Consequently, we aimed to investigate the effectiveness of a multidisciplinary and transitional nutritional intervention on health-related quality of life compared with standard care. METHODS: The study was a block randomized, observer-blinded clinical trial with two parallel arms. The Intervention Group was offered a multidisciplinary transitional nutritional intervention consisting of dietary counselling and six sub-interventions targeting individually assessed risk factors for malnutrition, while the Control Group received standard care. The inclusion criteria were a Mini Nutritional Assessment Short-Form score ≤11, age ≥65 years, and an acute admittance to the Emergency Department. Outcomes were assessed on admission and 8 and 16 weeks after hospital discharge. The primary outcome was the difference between groups in change in health-related quality of life (assessed by the EuroQol-5D-5L) from baseline to 16 weeks after discharge. The secondary outcomes were difference in intake of energy and protein, well-being, muscle strength, and body weight at all timepoints. RESULTS: From October 2018 to April 2021, 130 participants were included. Sixteen weeks after discharge, 29% in the Intervention Group and 19% in the Control Group were lost to follow-up. Compliance varied between the sub-interventions targeting nutritional risk factors and was generally low after discharge, ranging from 0 to 61%. No difference was found between groups on change in health-related quality of life or on well-being, muscle strength, and body weight at any timepoint, neither using the intention-to-treat analysis nor the per-protocol analysis. The protein intake was higher in the Intervention Group during hospitalization (1.1 (Standard Deviation (SD) 0.4) vs 0.8 (SD 0.5) g/kg/day, p = 0.0092) and 8 weeks after discharge (1.2 (SD 0.5) vs 0.9 (0.4) g/kg/day, p = 0.0025). The percentual intake of calculated protein requirements (82% (SD 24) vs 61% (SD 32), p = 0.0021), but not of calculated energy requirements (89% (SD 23) vs 80% (SD 37), p = 0.2), was higher in the Intervention Group than in the Control Group during hospitalization. Additionally, the Intervention Group had a significantly higher percentual intake of calculated protein requirements (94% (SD 41) vs 74% (SD 30), p = 0.015) and calculated energy requirements (115% (SD 37) vs 94% (SD 31), p = 0.0070) 8 weeks after discharge. The intake of energy and protein was comparable between the groups 16 weeks after discharge. CONCLUSION: We found no effect of a multidisciplinary and transitional nutritional intervention for acutely admitted medical patients aged ≥65 years with malnutrition or risk of malnutrition on our primary outcome, health-related quality of life 16 weeks after discharge. Nor did the intervention affect the secondary outcomes, well-being, muscle strength, and body weight from admission to 8 or 16 weeks after discharge. However, the intervention improved energy and protein intake during hospitalization and 8 weeks after discharge. Low compliance with the intervention after discharge may have compromised the effect of the intervention. The study is registered at ClinicalTrials.gov (identifier: NCT03741283).

Inhibition of Small Conductance Calcium-Activated Potassium (SK) Channels Prevents Arrhythmias in Rat Atria During ß-Adrenergic and Muscarinic Receptor Activation.

Sympathetic and vagal activation is linked to atrial arrhythmogenesis. Here we investigated the small conductance Ca2+-activated K+ (SK)-channel pore-blocker N-(pyridin-2-yl)-4-(pyridine-2-yl)thiazol-2-amine (ICA) on action potential (AP) and atrial fibrillation (AF) parameters in isolated rat atria during ß-adrenergic [isoprenaline (ISO)] and muscarinic M2 [carbachol (CCh)] activation. Furthermore, antiarrhythmic efficacy of ICA was benchmarked toward the class-IC antiarrhythmic drug flecainide (Fleca). ISO increased the spontaneous beating frequency but did not affect other AP parameters. As expected, CCh hyperpolarized resting membrane potential (-6.2 ± 0.9 mV), shortened APD90 (24.2 ± 1.6 vs. 17.7 ± 1.1 ms), and effective refractory period (ERP; 20.0 ± 1.3 vs. 15.8 ± 1.3 ms). The duration of burst pacing triggered AF was unchanged in the presence of CCh compared to control atria (12.8 ± 5.3 vs. 11.2 ± 3.6 s), while ß-adrenergic activation resulted in shorter AF durations (3.3 ± 1.7 s) and lower AF-frequency compared to CCh. Treatment with ICA (10 µM) in ISO -stimulated atria prolonged APD90 and ERP, while the AF burden was reduced (7.1 ± 5.5 vs. 0.1 ± 0.1 s). In CCh-stimulated atria, ICA treatment also resulted in APD90 and ERP prolongation and shorter AF durations. Fleca treatment in CCh-stimulated atria prolonged APD90 and ERP and abbreviated the AF duration to a similar extent as with ICA. Muscarinic activated atria constitutes a more arrhythmogenic substrate than ß-adrenoceptor activated atria. Pharmacological inhibition of SK channels by ICA is effective under both conditions and equally efficacious to Fleca.