The influence of myosin regulatory light chain phosphorylation on the contractile performance of fatigued mammalian skeletal muscle

ABSTRACT The myosm regulatory light chain (RLC) of type II fibres is phosphorylated by Ca2+ -calmodulin dependent myosin light chain kinase (skMLCK) during muscular activation. The purpose of this study was to explore the effect of skMLCK gene ablation on the fatigability of mouse skeletal muscles during repetitive stimulation. The absence of myosin RLC phosphorylation in skMLCK knockout muscles attenuated contractile performance without a significant metabolic cost. Twitch force was potentiated to a greater extent in wildtype muscles until peak force had diminished to ~60% of baseline (37.2 ± 0.05% vs. 14.3 ± 0.02%). Despite no difference in peak force (Po) and shortening velocity (Vo), rate of force development (+dP/dt) and shortening-induced deactivation (SID) were almost two-fold greater in WT muscles. The present results demonstrate that myosin RLC phosphorylation may improve contractile performance during fatigue; providing a contractile advantage to working muscles and protecting against progressive fatigue.

The convergence of psychopathy, self-rated vulnerability, and other-rated vulnerability

Previous research has found that victims of crime tend to exhibit asynchronous movement (e.g. Grayson & Stein, 1981), and the fact that victims display different body language suggests that they may be sending inadvertent signals to their own vulnerability (e.g. Murzynski & Degelman, 1996). Body language has also be en linked with s e l f identification as a victim (Wheeler et aI., 2009), and self-identification has be en found to act as a proxy for more severe victimization (Baumer, 2002) and greater fear of crime (Greenberg & Beach, 2004). The first prediction in the present study, then, was that self-perceived vulnerability would be correlated with body language, while number of previous victimizations mayor may not show the same relationship. Findings from the present study indicate that self-perceived vulnerability exhibits a positive correlation with the body language cues that approaches significance r (10) = .45,p =.07, one-tailed. Different types of victimization, however, were not significantly correlated with these cues. A second goal of the study was to examine the relationship between psychopathic traits and accuracy in judgments of vulnerability. Seventy male participants rated the vulnerability of 12 female targets filmed walking down a hallway who had provided selfratings of vulnerability. Individuals scoring higher on Factor 2 and total psychopathy were significantly less discrepant from target self-rat~ngs of vulnerability, r (64) = - .39,p < .001; r (64) = - .29,p >.01, respectively. The final purpose of this study was to determine which body language cues were mos t salient to raters when making judgments of vulnerability. Participants rated the apparent vulnerability of a target in 7 video clips portraying each body language cue in isolation and a natural walk. Results of repeated measures analyses indicate that the videos rated as most vulnerable to victimization were those displaying low energy and l a ck of synchrony, followed by wide stride, short stride, and stiffknees, while the video displaying ne ck stiffness did not receive significantly different ratings from the mode l ' s natural walk. Replication with a larger sample size is necessary to increase confidence in findings and implications.

In Search of Convergence: A Co-citation Analysis of Three Sport Management Journals

Responding to a series of articles in sport management literature calling for more diversity in terms of areas of interest or methods, this study warns against the danger of excessively fragmenting this field of research. The works of Kuhn (1962) and Pfeffer (1993) are taken as the basis of an argument that connects convergence with scientific strength. However, being aware of the large number of counterarguments directed at this line of reasoning, a new model of convergence, which focuses on clusters of research contributions with similar areas of interest, methods, and concepts, is proposed. The existence of these clusters is determined with the help of a bibliometric analysis of publications in three sport management journals. This examination determines that there are justified reasons to be concerned about the level of convergence in the field, pointing out to a reduced ability to create large clusters of contributions in similar areas of interest.

The Effectiveness of Learning Portfolios: A Study of Quality Assurance Programs of Selected Health Regulatory Colleges in Ontario

Health regulatory colleges promote quality practice and continued competence through Quality Assurance (QA) programs. For many colleges, a QA program includes the use of portfolios that incorporate self-directed learning. The purpose of this study was to determine some of the issues surrounding the effectiveness of QA portfolio programs. The literature review revealed that portfolios are valuable tools, but gaps in knowledge include a comparative analysis of QA programs and the perspective of regulatory college administrators. Data were collected through interviews with 6 administrators and a review of 14 portfolio models described on college websites. The results from the two data sources were applied to Robert Stake's responsive evaluation framework to identify issues related to the portfolio's effectiveness (Stake, 1967). The learning components of portfolios were analyzed through the humanist and constructivist lenses. All 14 portfolio models were found to have 3 main components: self-diagnosis, learning plan and activities, and self-evaluation. However, differences were uncovered in learners' autonomy in selecting learning activities, methods of portfolio evaluation, and the relationship between the portfolio and other QA components. The results revealed a dual philosophy of learning in portfolio models and an apparent contradiction between the needs of the individual learner and the organization. Paths for future research include the tenuous relationship between competence and learning, and the impact of technical approaches on selfdirected learning initiatives. A key recommendation is to acknowledge the unique identity of each profession so that health regulatory colleges can address legislative demands and learner needs.

Myosin Regulatory Light Chain Phosphorylation and Its Effect on the Contractile Economy of Mouse Fast Muscle

Activated by elevations in myoplasmic calcium concentration, myosin light chain kinase (skMLCK) phosphorylates the regulatory light chains (RLCs) of fast muscle myosin. This covalent modification potentiates force production, but requires an investment of ATP. Our objective was to investigate the effect of RLC phosphorylation on the contractile economy (mechanical output:metabolic input) of fast twitch skeletal muscle. Extensor digitorum longus muscles isolated from Wildtype and skMLCK-/- mice mounted in vitro (25°C) were subjected to repetitive low-frequency stimulation (10Hz,15s) known to cause activation of skMLCK, and staircase potentiation of force. With a 3-fold increase in RLC phosphate content, Wildtype generated 44% more force than skMLCK-/- muscles over the stimulation period (P = .002), without an accompanied increase in energy cost (P = .449). Overall, the contractile economy of Wildtype muscles, with an intact RLC phosphorylation mechanism, was 73% greater than skMLCK /- muscles (P = .043), demonstrating an important physiological function of skMLCK during repetitive contractile activity.