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Acidosis (low pH) is the oldest putative agent of muscular fatigue, but the molecular mechanism underlying its depressive effect on muscular performance remains unresolved. Therefore, the effect of low pH on the molecular mechanics and kinetics of chicken skeletal muscle myosin was studied using in vitro motility (IVM) and single molecule laser trap assays. Decreasing pH from 7.4 to 6.4 at saturating ATP slowed actin filament velocity (Vactin) in the IVM by 36%. Single molecule experiments, at 1 µMATP, decreased the average unitary step size of myosin (d) from 10 ± 2 nm (pH 7.4) to 2 ± 1 nm (pH 6.4). Individual binding events at low pH were consistent with the presence of a population of both productive (average d = 10 nm) and nonproductive (average d = 0 nm) actomyosin interactions. Raising the ATP concentration from 1 µM to 1 mM at pH 6.4 restored d (9 ± 3 nm), suggesting that the lifetime of the nonproductive interactions is solely dependent on the [ATP]. Vactin, however, was not restored by raising the [ATP] (1-10 mM) in the IVM assay, suggesting that low pH also prolongs actin strong binding (ton). Measurement of ton as a function of the [ATP] in the single molecule assay suggested that acidosis prolongs ton by slowing the rate of ADP release. Thus, in a detachment limited model of motility (i.e., Vactin ~ d/ton), a slowed rate of ADP release and the presence of nonproductive actomyosin interactions could account for the acidosis-induced decrease in Vactin, suggesting a molecular explanation for this component of muscular fatigue. [ABSTRACT FROM AUTHOR]

Increases in Pi combined with decreases in myoplasmic Ca2+ are believed to cause a significant portion of the decrease in muscular force during fatigue. To investigate this further, we determined the effect of 30 mM Pi on the force-Ca2+ relationship of chemically skinned single muscle fibers at near-physiological temperature (30°C). Fibers isolated from rat soleus (slow) and gastrocnemius (fast) muscle were subjected to a series of solutions with an increasing free Ca2+ concentration in the presence and absence of 30 mM Pi at both low (15°C) and high (30°C) temperature. In slow fibers, 30 mM Pi significantly increased the Ca2+ required to elicit measurable force, referred to as the activation threshold at both low and high temperatures; however, the effect was twofold greater at the higher temperature. In fast fibers, the activation threshold was unaffected by elevating Pi at 15°C but was significantly increased at 30°C. At both low and high temperatures, 30 mM Pi increased the Ca2+ required to elicit half-maximal force (pCa50) in both slow and fast fibers, with the effect of Pi twofold greater at the higher temperature. These data suggest that during fatigue, reductions in the myoplasmic Ca2+ and increases in Pi act synergistically to reduce muscular force. Consequently, the combined changes in these ions likely account for a greater portion of fatigue than previously predicted based on studies at lower temperatures or high temperatures at saturating Ca2+ levels. [ABSTRACT FROM AUTHOR]

Elevated levels of Pi are thought to cause a substantial proportion of the loss in muscular force and power output during fatigue from intense contractile activity. However, support for this hypothesis is based, in part, on data from skinned single fibers obtained at low temperatures (≤ 15 °C). The effect of high (30 mM) Pi concentration on the contractile function of chemically skinned single fibers was examined at both low (15°C) and high (30°C) temperatures using fibers isolated from rat soleus (type I fibers) and gastrocnemius (type II fibers) muscles. Elevating Pi from 0 to 30 mM at saturating free Ca2+ levels depressed maximum isometric force (Po) by 54% at 15°C and by 19% at 30°C (P < 0.05; significant interaction) in type I fibers. Similarly, the Po of type II fibers was significantly more sensitive to high levels of Pi at the lower (50% decrease) vs. higher temperature (5% decrease). The maximal shortening velocity of both type I and type II fibers was not significantly affected by elevated Pi at either temperature. However, peak fiber power was depressed by 49% at 15°C but by only 16% at 30°C in type I fibers. Similarly, in type II fibers, peak power was depressed by 40 and 18% at 15 and 30°C, respectively. These data suggest that near physiological temperatures and at saturating levels of intracellular Ca2+, elevated levels of Pi contribute less to fatigue than might be inferred from data obtained at lower temperatures. [ABSTRACT FROM AUTHOR]

Multiscale models aiming to connect muscle's molecular and cellular function have been difficult to develop, in part due to a lack of self-consistent multiscale data. To address this gap, we measured the force response from single, skinned rabbit psoas muscle fibers to ramp shortenings and step stretches performed on the plateau region of the force-length relationship. We isolated myosin from the same muscles and, under similar conditions, performed single-molecule and ensemble measurements of myosin's ATP-dependent interaction with actin using laser trapping and in vitro motility assays. We fit the fiber data by developing a partial differential equation model that includes thick filament activation, whereby an increase in force on the thick filament pulls myosin out of an inhibited state. The model also includes a series elastic element and a parallel elastic element. This parallel elastic element models a titin-actin interaction proposed to account for the increase in isometric force after stretch (residual force enhancement). By optimizing the model fit to a subset of our fiber measurements, we specified seven unknown parameters. The model then successfully predicted the remainder of our fiber measurements and also our molecular measurements from the laser trap and in vitro motility. The success of the model suggests that our multiscale data are self-consistent and can serve as a testbed for other multiscale models. Moreover, the model captures the decrease in isometric force observed in our muscle fibers after active shortening (force depression), suggesting a molecular mechanism for force depression, whereby a parallel elastic element combines with thick filament activation to decrease the number of cycling cross-bridges., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 Biophysical Society. Published by Elsevier Inc. All rights reserved.)

Multiscale models aiming to connect muscle's molecular and cellular function have been difficult to develop, in part, due to a lack of self-consistent multiscale data. To address this gap, we measured the force response from single skinned rabbit psoas muscle fibers to ramp shortenings and step stretches performed on the plateau region of the force-length relationship. We isolated myosin from the same muscles and, under similar conditions, performed single molecule and ensemble measurements of myosin's ATP-dependent interaction with actin using laser trapping and in vitro motility assays. We fit the fiber data by developing a partial differential equation model that includes thick filament activation, whereby an increase in force on the thick filament pulls myosin out of an inhibited state. The model also includes a series elastic element and a parallel elastic element. This parallel elastic element models a titin-actin interaction proposed to account for the increase in isometric force following stretch (residual force enhancement). By optimizing the model fit to a subset of our fiber measurements, we specified seven unknown parameters. The model then successfully predicted the remainder of our fiber measurements and also our molecular measurements from the laser trap and in vitro motility. The success of the model suggests that our multiscale data are self-consistent and can serve as a testbed for other multiscale models. Moreover, the model captures the decrease in isometric force observed in our muscle fibers after active shortening (force depression), suggesting a molecular mechanism for force depression, whereby a parallel elastic element combines with thick filament activation to decrease the number of cycling cross-bridges.

Adverse drug events (ADEs) and adverse drug reactions (ADRs) are leading causes of iatrogenic injury, which can result in emergency department (ED) visits or admissions to inpatient wards. The aim of this systematic review and meta-analysis was to provide up-to-date estimates of the prevalence of (preventable) drug-related ED visits and hospital admissions, as well as the type and prevalence of implicated ADRs/ADEs and drugs. A literature search of studies published between January 2012 and December 2021 was performed in PubMed, Medline, EMBASE, Cochrane Library, and Web of Science. Retrospective and prospective observational studies investigating acute admissions to EDs or inpatient wards due to ADRs or ADEs in the general population were included. Meta-analyses of prevalence rates were conducted using generalized linear mixed models (GLMM) with the random-effect method. Seventeen studies reporting ADRs and/or ADEs were eligible for inclusion. The prevalence rates of ADR- and ADE-related admissions to EDs or inpatient wards were estimated at 8.3% ([95% CI, 6.4-10.7%]) and 13.9% ([95% CI, 8.1-22.8%]), respectively, of which almost half (ADRs: 44.7% [95% CI: 28.1; 62.4]) and more than two thirds (ADEs: 71.0% [95% CI, 65.9-75.6%]) had been classified as at least possibly preventable. The ADR categories most frequently implicated in ADR-related admissions were gastrointestinal disorders, electrolyte disturbances, bleeding events, and renal and urinary disorders. Nervous system drugs were found to be the most commonly implicated drug groups, followed by cardiovascular and antithrombotic agents. Our findings demonstrate that ADR-related admissions to EDs and inpatient wards still represent a major and often preventable health care problem. In comparison to previous systematic reviews, cardiovascular and antithrombotic drugs remain common causes of drug-related admissions, while nervous system drugs appear to have become more commonly implicated. These developments may be considered in future efforts to improve medication safety in primary care.

Knowledge of social inequalities in monoclonal gammopathy of undetermined significance (MGUS) will contribute to understanding multiple myeloma (MM) etiology, as MGUS consistently precedes MM. The aim of the present study was to examine whether socioeconomic position (SEP) is associated with MGUS in a population-based cohort including information on potential MGUS risk factors. Overall, 4787 study participants aged 45-75 years with information on MGUS were included. SEP indicators (education, income) and potential risk factors (i.e., body mass index, diabetes, smoking, dietary factors) were assessed at baseline. Overall, 260 MGUS cases were detected at baseline and prospectively over a 10-year follow-up. In age-adjusted logistic regression models, a lower chance of having MGUS at baseline or developing MGUS during 10 years of follow-up was indicated for groups of low SEP with odds ratios (OR) of 0.39 (95% confidence interval [95%-CI] 0.19-0.76) for women and 0.48 (95% CI 0.10-1.16) for men in the lowest compared to the highest educational group. After additionally including potential mediating risk factors in the regression models, the estimated ORs changed only slightly in magnitude. Similar results were obtained for income. Current smoking and low fruit consumption were associated with MGUS independently of SEP in women, but not in men. The present study indicates a lower MGUS risk in lower SEP groups. Supporting evidence is given that smoking and diet play a role in the development of MGUS independently of SEP, while it has to be assumed that risk factors unknown to date are responsible for the observed social inequalities in MGUS.

The effects of preexercise feeding on responses to endurance exercise and performance were investigated. Untrained adolescent boys (N = 13, age 14.9 +/- 0.5 years) completed three endurance test sessions separated by a minimum of 72 hr. Each session consisted of 75 min of cycling at 60% of VO2 max followed by a high-intensity performance test. Dietary conditions were a candy bar (C1: 280 kcal, 36 g CHO), fat-free fig bars (C2: 200 kcal, 44 g CHO), and a nonnutritive sweetened drink (C3: placebo), ingested 10 min prior to exercise. Respiratory gases, heart rate, blood glucose, and lactate concentrations were measured throughout the test. ANOVA results revealed significant time effects for all variables; however, no differences were seen among the conditions. Performance times, 311.9 +/- 38.5 s in C1, 316.2 +/- 37.3 s in C2, and 328.1 +/- 46.4 s in C3, were not significantly different among conditions. Thus, preexercise feeding did not affect responses to endurance exercise or performance in adolescent boys.