Developing and Demonstrating the Viability and Availability of the Multilevel Implementation Strategy for Syncope Optimal Care Through Engagement (MISSION) Syncope App: Evidence-Based Clinical Decision Support Tool.

BACKGROUND: Syncope evaluation and management is associated with testing overuse and unnecessary hospitalizations. The 2017 American College of Cardiology/American Heart Association (ACC/AHA) Syncope Guideline aims to standardize clinical practice and reduce unnecessary services. The use of clinical decision support (CDS) tools offers the potential to successfully implement evidence-based clinical guidelines. However, CDS tools that provide an evidence-based differential diagnosis (DDx) of syncope at the point of care are currently lacking. OBJECTIVE: With input from diverse health systems, we developed and demonstrated the viability of a mobile app, the Multilevel Implementation Strategy for Syncope optImal care thrOugh eNgagement (MISSION) Syncope, as a CDS tool for syncope diagnosis and prognosis. METHODS: Development of the app had three main goals: (1) reliable generation of an accurate DDx, (2) incorporation of an evidence-based clinical risk tool for prognosis, and (3) user-based design and technical development. To generate a DDx that incorporated assessment recommendations, we reviewed guidelines and the literature to determine clinical assessment questions (variables) and likelihood ratios (LHRs) for each variable in predicting etiology. The creation and validation of the app diagnosis occurred through an iterative clinician review and application to actual clinical cases. The review of available risk score calculators focused on identifying an easily applied and valid evidence-based clinical risk stratification tool. The review and decision-making factors included characteristics of the original study, clinical variables, and validation studies. App design and development relied on user-centered design principles. We used observations of the emergency department workflow, storyboard demonstration, multiple mock review sessions, and beta-testing to optimize functionality and usability. RESULTS: The MISSION Syncope app is consistent with guideline recommendations on evidence-based practice (EBP), and its user interface (UI) reflects steps in a real-world patient evaluation: assessment, DDx, risk stratification, and recommendations. The app provides flexible clinical decision making, while emphasizing a care continuum; it generates recommendations for diagnosis and prognosis based on user input. The DDx in the app is deemed a pragmatic model that more closely aligns with real-world clinical practice and was validated using actual clinical cases. The beta-testing of the app demonstrated well-accepted functionality and usability of this syncope CDS tool. CONCLUSIONS: The MISSION Syncope app development integrated the current literature and clinical expertise to provide an evidence-based DDx, a prognosis using a validated scoring system, and recommendations based on clinical guidelines. This app demonstrates the importance of using research literature in the development of a CDS tool and applying clinical experience to fill the gaps in available research. It is essential for a successful app to be deliberate in pursuing a practical clinical model instead of striving for a perfect mathematical model, given available published evidence. This hybrid methodology can be applied to similar CDS tool development.

Planning Implementation Success of Syncope Clinical Practice Guidelines in the Emergency Department Using CFIR Framework.

Background and Objectives: Overuse and inappropriate use of testing and hospital admission are common in syncope evaluation and management. Though guidelines are available to optimize syncope care, research indicates that current clinical guidelines have not significantly impacted resource utilization surrounding emergency department (ED) evaluation of syncope. Matching implementation strategies to barriers and facilitators and tailoring strategies to local context hold significant promise for a successful implementation of clinical practice guidelines (CPG). Our team applied implementation science principles to develop a stakeholder-based implementation strategy. Methods and Materials: We partnered with patients, family caregivers, frontline clinicians and staff, and health system administrators at four health systems to conduct quantitative surveys and qualitative interviews for context assessment. The identification of implementation strategies was done by applying the CFIR-ERIC Implementation Strategy Matching Tool and soliciting stakeholders' inputs. We then co-designed with patients and frontline teams, and developed and tested specific strategies. Results: A total of 114 clinicians completed surveys and 32 clinicians and stakeholders participated in interviews. Results from the surveys and interviews indicated low awareness of syncope guidelines, communication challenges with patients, lack of CPG protocol integration into ED workflows, and organizational process to change as major barriers to CPG implementation. Thirty-one patients and their family caregivers participated in interviews and expressed their expectations: clarity regarding their diagnosis, context surrounding care plan and diagnostic testing, and a desire to feel cared about. Identifying change methods to address the clinician barriers and patients and family caregivers expectations informed development of the multilevel, multicomponent implementation strategy, MISSION, which includes patient educational materials, mentored implementation, academic detailing, Syncope Optimal Care Pathway and a corresponding mobile app, and Lean quality improvement methods. The pilot of MISSION demonstrated feasibility, acceptability and initial success on appropriate testing. Conclusions: Effective multifaceted implementation strategies that target individuals, teams, and healthcare systems can be employed to plan successful implementation and promote adherence to syncope CPGs.

Preoperative Optimism Related to Low Anxiety in Patients 1 Month After Open Heart Surgery.

Anxiety can contribute to poor prognosis in cardiac patients. Few studies have examined the role of optimism in anxiety after open heart surgery (OHS). This study investigated the influence of preoperative optimism on post-OHS anxiety, adjusting cardiac indices used by cardiac surgeons. Data were collected before and 1 month after OHS in 481 patients (58% men; age, 62.4 ± 11.94 years). Optimism was measured using the Life Orientation Test. Anxiety was measured using the Trait Anxiety Inventory. Medical and cardiac indices were retrieved from the Society of Thoracic Surgeon's national database. Multiple regression analyses showed that greater pre-OHS optimism was associated with lower levels of post-OHS anxiety (F[6, N = 306] = 50.18, p < 0.001, R = 0.502). No other factors showed similar protection. Pre-OHS anxiety, younger age, and minority status were associated with anxiety in the critical recovery month. The findings demonstrate the potential benefit of optimism against post-OHS anxiety, which may have clinical implications for improving disease management.

Gender differences in management of patients undergoing catheter ablation of atrioventricular nodal reentry tachycardia.

BACKGROUND: Atrioventricular nodal reentrant tachycardia (AVNRT) is the most common type of supraventricular tachycardia (SVT). Similar to other cardiac tests and interventions, gender bias may influence clinical decision making in providing appropriate care for AVNRT patients. We assessed for gender differences in the diagnosis and management of AVNRT patients who underwent catheter ablation. METHODS: Patients who underwent catheter ablation for AVNRT were included. We explored the gender difference on various clinical parameters such as the time from SVT symptoms, SVT diagnosis, and first electrophysiology consult to time of catheter ablation. RESULTS: Among 140 patients screened, 116 patients met the inclusion criteria, including 67.2% women. Median time from symptoms onset to SVT diagnosis was 18.5 months (interquartile range [IQR] 4.0-58.5) in women versus 4.0 months (0.75-34.7) in men, P = .005. Once SVT was diagnosed, women took a median of 12.5 months (IQR 3.0-57.0) to proceed with ablation versus 3.0 months (1.0-7.0) for men, P ≤ .001. It took a longer time from the first electrophysiology consultation to ablation: 54.5 days (20.75-144.75) for women versus 20.5 days (6.0-46.25) for men, P = .008. Overall, it took 60.0 months (IQR 12.8-132.0) for women to have an ablation from initial symptoms onset versus 15 months (IQR 4.6-48.0) for men, P = .001. Prior to ablation, women had 3.78 ± 3.79 (mean ± SD) emergency department visits for SVT versus men 1.52 ± 1.72 and women tried 1.28 ± 0.82 medications versus men 0.76 ± 0.68, P < .001 and .001, respectively. CONCLUSIONS: This study demonstrates significant and multifactorial gender-related disparities in AVNRT diagnosis and treatment. Larger studies are needed to confirm these results.

Development transitions of thin filament proteins in rat extraocular muscles.

Extraocular muscles are a unique subset of striated muscles. During postnatal development, the extraocular muscles undergo a number of myosin isoform transitions that occur between postnatal day P10 (P10) and P15. These include: (1) loss of embryonic myosin from the global layer resulting in the expression restricted to the orbital layer; (2) the onset of expression of extraocular myosin and the putative tonic myosin (myh 7b/14); and (3) the redistribution of nonmuscle myosin IIB from a subsarcolemmal position to a sarcomeric distribution in the slow fibers of the global layer. For this study, we examined the postnatal appearance and distribution of α-actinin, tropomyosin, and nebulin isoforms during postnatal development of the rat extraocular muscles. Although sarcomeric α-actinin is detectable from birth, α-actinin 3 appears around P15. Both tropomyosin-1 and -2 are present from birth in the same distribution as in the adult animal. The expression of nebulin was monitored by gel electrophoresis and western blots. At P5-10, nebulin exhibits a lower molecular mass than observed P15 and later during postnatal development. The changes in α-actinin 3 and nebulin expression between P10 and P15 coincide with transitions in myosin isoforms as detailed above. These data point to P10-P15 as the critical period for the maturation of the extraocular muscles, coinciding with eyelid opening.

Using the consolidated framework for implementation research (CFIR) to guide implementation of cardio-oncology services.

Introduction: Cardio-oncology focuses on diagnosing and preventing adverse cardiovascular outcomes in cancer patients. Interdisciplinary cardio-oncology services address the spectrum of prevention, detection, monitoring, and treatment of cancer patients at risk of cardio-toxicity and aim to improve the continuum of cardiac care for oncology patients. The goal of this study was to engage clinician and administrative stakeholders to assess multilevel needs, barriers, and expectations regarding cardio oncology services. Methods: We interviewed clinicians and administrators at an academic medical center using the Consolidated Framework for Implementation Research (CFIR) to understand multilevel determinants influencing cardio-oncology service implementation. We also conducted a web-based survey to assess the knowledge, attitude, and perceptions of cardio-oncology services held by local and regional clinicians who may refer cardio-oncology patients to the study site. Results: Multiple facilitators to cardio-oncology service implementation emerged. Interview participants believed cardio-oncology services could benefit patients and the organization by providing a competitive advantage. A majority (74%) of clinicians surveyed thought a cardio-oncology service would significantly improve cancer patients' prognoses. Implementation barriers discussed included costs and a siloed organizational structure that complicated cross-service collaboration. In the clinician survey, differences in the views toward cardio-oncology services held by cardiology versus oncology providers would need to be negotiated in future cardio-oncology service development. For example, while most providers accepted similar risk of cardio-toxicity when consenting patients for cancer therapy in a curative setting, cardiologists accepted significantly higher levels of risk than oncologists in an incurable setting: 75% of oncologists accepted 1-5% risk; 77% of cardiologists accepted ≥5% risk). Conclusions: Participants supported implementation and development of cardio-oncology services. Respondents also noted multi-level barriers that could be addressed to maximize the potential for success. Engaging administrators and clinicians from cardiology and oncology disciplines in the future development of such services can help ensure maximal relevance and uptake.

Co-designing and piloting educational materials with patients and healthcare providers for syncope in the emergency department.

Objective: The purpose of this study was to identify barriers and design interventions to promote adherence to 2017 Guideline for Syncope Evaluation and Management. Methods: Focus groups and interviews were conducted to understand preferences, needs and barriers from patients and providers. Educational materials for patients were developed following a co-design, iterative process with patients, providers and hospital staff. The academic medical center's (AMC) Patient Education Department and Patient & Family Advisory Council reviewed materials to ensure health literacy. We piloted usability and feasibility of delivering the materials to a small cohort of patients. Results: From Feb to March 2020, 24 patients were asked to watch the video. Twenty-two watched the intake video; of those 8 watched the discharge video. 95% of participants found the intake video informational and 86% would recommend it to others; 100% found the discharge video informational and would recommend it to others. Patients who watched both videos reported the videos improved their overall stay. Conclusion: Our study described a patient-clinician-researcher codesign process and demonstrated feasibility of tools developed to communicate risk and uncertainty with patients and facilitate shared decision making in syncope evaluation. Innovation: Engaging end users in developing interventions is critical for sustained practice change.

Current and future therapies to treat impaired awareness of hypoglycemia.

In order to achieve optimal glycemic control, intensive insulin regimes are needed for individuals with Type 1 Diabetes (T1D) and insulin-dependent Type 2 Diabetes (T2D). Unfortunately, intensive glycemic control often results in insulin-induced hypoglycemia. Moreover, recurrent episodes of hypoglycemia result in both the loss of the characteristic warning symptoms associated with hypoglycemia and an attenuated counterregulatory hormone responses. The blunting of warning symptoms is known as impaired awareness of hypoglycemia (IAH). Together, IAH and the loss of the hormonal response is termed hypoglycemia associated autonomic failure (HAAF). IAH is prevalent in up to 25% in people with T1D and up to 10% in people with T2D. IAH and HAAF increase the risk of severe hypoglycemia 6-fold and 25-fold, respectively. To reduce this risk for severe hypoglycemia, multiple different therapeutic approaches are being explored that could improve awareness of hypoglycemia. Current therapies to improve awareness of hypoglycemia include patient education and psychoeducation, the use of novel glycemic control technology, pancreas/islet transplantation, and drug therapy. This review examines both existing therapies and potential therapies that are in pre-clinical testing. Novel treatments that improve awareness of hypoglycemia, via improving the counterregulatory hormone responses or improving hypoglycemic symptom recognition, would also shed light on the possible neurological mechanisms that lead to the development of IAH. To reduce the risk of severe hypoglycemia in people with diabetes, elucidating the mechanism behind IAH, as well as developing targeted therapies is currently an unmet need for those that suffer from IAH.

KL2 scholars' perceptions of factors contributing to sustained translational science career success.

Introduction: Identifying the most effective ways to support career development of early stage investigators in clinical and translational science should yield benefits for the biomedical research community. Institutions with Clinical and Translational Science Awards (CTSA) offer KL2 programs to facilitate career development; however, the sustained impact has not been widely assessed. Methods: A survey comprised of quantitative and qualitative questions was sent to 2144 individuals that had previously received support through CTSA KL2 mechanisms. The 547 responses were analyzed with identifying information redacted. Results: Respondents held MD (47%), PhD (36%), and MD/PhD (13%) degrees. After KL2 support was completed, physicians' time was divided 50% to research and 30% to patient care, whereas PhD respondents devoted 70% time to research. Funded research effort averaged 60% for the cohort. Respondents were satisfied with their career progression. More than 95% thought their current job was meaningful. Two-thirds felt confident or very confident in their ability to sustain a career in clinical and translational research. Factors cited as contributing to career success included protected time, mentoring, and collaborations. Conclusion: This first large systematic survey of KL2 alumni provides valuable insight into the group's perceptions of the program and outcome information. Former scholars are largely satisfied with their career choice and direction, national recognition of their expertise, and impact of their work. Importantly, they identified training activities that contributed to success. Our results and future analysis of the survey data should inform the framework for developing platforms to launch sustaining careers of translational scientists.

"Passing Out is a Serious Thing": Patient Expectations for Syncope Evaluation and Management.

PURPOSE: Syncope is a complex symptom requiring thoughtful evaluation. The ACC/AHA/HRS published syncope management guidelines in 2017. Effective guideline implementation hinges on overcoming multilevel barriers, including providers' perceptions that patients prefer aggressive diagnostic testing when presenting to the emergency department (ED) with syncope, which conflicts with the 2017 Guideline on Syncope. To better understand this perceived barrier, we explored patient and family caregiver expectations and preferences when presenting to the ED with syncope. PATIENTS AND METHODS: We conducted semi-structured focus groups (N=12) and in-depth interviews (N=19) with patients presenting to the ED with syncope as well as with their family caregivers. Interviews were recorded, transcribed verbatim, and analyzed by a team of researchers following a directed content analysis. Results were reviewed and shared iteratively with all team members to confirm mutual understanding and agreement. RESULTS: Syncope patients and caregivers discussed three main desires when presenting to the ED with syncope: 1) clarity regarding their diagnosis,; 2) context surrounding their care plan and diagnostic approach; and 3) to feel seen, heard and cared about by their health care team. CONCLUSION: Clinicians have cited patient preferences for aggressive diagnostic testing as a barrier to adhering to the 2017 Guideline on Syncope, which recommends against routine administration of imaging testing (eg, echocardiograms). Our results suggest that while participants preferred diagnostic testing as a means to achieve clarity and even a feeling of being cared for, other strategies, such as a patient-engaged approach to communication and shared decision-making, may address the spectrum of patient expectations when presenting to the ED with syncope while adhering to guideline recommendations.

Biobehavioral Measures of Presbylaryngeus.

OBJECTIVE: The objective of this observational study was to assess the relationship between established aging biobehavioral measures and voice decline in normally aging adults. STUDY DESIGN: Cross-sectional study. METHODS: Participants 60-85 years of age were divided into two age and sex-matched groups, based on the presence or absence of presbylaryngeus. Both groups underwent a battery of tests measuring anthropometric variables, inflammatory markers, general health measures, and vocal function parameters. Differences from the norm were calculated for all variables. Parametric and nonparametric tests were performed to assess group differences. In addition, variable selection analysis was performed to determine variables that were most influential in predicting the occurrence of presbylaryngeus in our current sample. RESULTS: Fifty-three participants were divided into age and sex-matched groups of "presbylaryngeus" (n = 26) and "non-presbylaryngeus" (n = 27). The two groups were statistically different in select measures of inflammatory markers, general health measures, and vocal function parameters. Anthropometric measures were not statistically different. Based on variable selection, the variables most predictive of the presence of presbylaryngeus were measures of the Physical Activity Scale of the Elderly, C-reactive protein, laryngeal airway resistance, and vocal roughness. CONCLUSIONS: In addition to group differences in vocal function measures, results for the presbylaryngeus group consistently trended sub-optimally on anthropometric measures, two inflammatory markers, and general health measures. These results suggest that this sample of individuals with presbylaryngeus demonstrated greater biobehavioral deficits associated with aging as compared to age and sex-matched non-presbylaryngeus individuals.

Securing the Future for a Major Academic Cardiovascular Program: Hardwiring a Referral Network and Preparing for a Transition to Value-Based Reimbursement.

The University of Kentucky College of Medicine and Albert B. Chandler Hospital opened over 50 years ago to serve Kentucky. After initial growth and expansion, both were struggling clinically, academically, and financially in the early 2000s. Difficulties were apparent in cardiovascular (CV) services, which captured only 11% of the regional patients hospitalized for cardiac disease. Over the next 15 years, CV services dynamically transformed to become the leading provider with a large network of regional partners, garnering 42% of market share. This article describes strategic plans and initiatives leading to clinical and academic growth. Future value-based initiatives are also described.

Differential role of von Willebrand factor and P-selectin on microvascular thrombosis in endotoxemia.

OBJECTIVE: Endotoxin (lipopolysaccharide [LPS]) enhances microvascular thrombosis in mouse cremaster venules. Because von Willebrand factor (vWF) and P-selectin are suggested to mediate LPS-induced platelet-microvessel interactions, we determined whether vWF and P-selectin contribute to microvascular thrombosis in endotoxemia. METHODS AND RESULTS: A light/dye-induced thrombosis model was used in cremaster microvessels of saline or LPS-injected mice (wild-type, P-selectin-deficient, vWF-deficient, or littermate controls). In each strain except vWF-deficient mice, LPS enhanced thrombosis in venules, resulting in approximately 30% to 55% reduction in times to thrombotic occlusion. LPS had no effect on thrombosis in vWF-deficient mice, although these mice had similar systemic responses to LPS (tachycardia, thrombocytopenia, and plasma coagulation markers). vWF-deficient mice demonstrated prolonged times to thrombotic occlusion relative to littermates. LPS increased plasma vWF in each strain studied. While immunofluorescence in wild-type mice failed to detect LPS-induced differences in microvascular vWF expression, it revealed markedly higher vWF expression in venules relative to arterioles. CONCLUSIONS: vWF mediates light/dye-induced microvascular thrombosis and endotoxin-induced enhancement of thrombosis in mouse cremaster venules; P-selectin is not required for enhanced thrombosis in response to endotoxin. Enhanced vWF expression in venules relative to arterioles has potential implications for the differences in thrombotic responses among these microvessels.

Subcutaneous Neurotrophin 4 Infusion Using Osmotic Pumps or Direct Muscular Injection Enhances Aging Rat Laryngeal Muscles.

Laryngeal dysfunction in the elderly is a major cause of disability, from voice disorders to dysphagia and loss of airway protective reflexes. Few, if any, therapies exist that target age-related laryngeal muscle dysfunction. Neurotrophins are involved in muscle innervation and differentiation of neuromuscular junctions (NMJs). It is thought that neurotrophins enhance neuromuscular transmission by increasing neurotransmitter release. The neuromuscular junctions (NMJs) become smaller and less abundant in aging rat laryngeal muscles, with evidence of functional denervation. We explored the effects of NTF4 for future clinical use as a therapeutic to improve function in aging human laryngeal muscles. Here, we provide the detailed protocol for systemic application and direct injection of NTF4 to investigate the ability of aging rat laryngeal muscle to remodel in response to NTF4 application. In this method, rats either received NTF4 either systemically via osmotic pump or by direct injection through the vocal folds. Laryngeal muscles were then dissected and used for histological examination of morphology and age-related denervation.

Contractile dysfunction and altered metabolic profile of the aging rat thyroarytenoid muscle.

The larynx and its muscles are important for ventilation, coughing, sneezing, swallowing, Valsalva's maneuver, and phonation. Because of their functional demands, the intrinsic laryngeal muscles have a unique phenotype: very small and fast fibers with high mitochondrial content. How aging affects their function is largely unknown. In this study, we tested the hypothesis that an intrinsic laryngeal muscle (thyroarytenoid muscle, a vocal fold adductor) would become weaker, slower, and fatigable with age. Muscles from Fischer 344 x Brown Norway F1 hybrid rats (6, 18, and 30 mo of age) were used for in vitro contractile function and histology. Thyroarytenoid muscles generated significantly lower twitch and tetanic forces at 30 mo vs. 6 and 18 mo. Maximal shortening velocity decreased by 20% at 30 mo (vs. 6 mo), and velocity of unloaded shortening was slower at 18 and 30 mo by 19 and 27% vs. 6 mo. There was no histochemical evidence of altered myosin ATPase activity at 18 or 30 mo of age. Fatigue resistance was significantly decreased at 18 and 30 mo. We also found abundant mitochondrial clusters and ragged red fibers in the muscles of 30-mo-old rats, and there was an age-related increase in glycogen-positive fibers. We conclude that rat thyroarytenoid muscles become weaker, slower, and more fatigable with age. These functional changes are not due to alterations in myosin ATPase activity, but a switch in the expression of myosin isoforms remains a possibility. Finally, the alterations in mitochondrial and glycogen content indicate a shift in the metabolic characteristics of these muscles with age.

Enhancement of aging rat laryngeal muscles with endogenous growth factor treatment.

Clinical evidence suggests that laryngeal muscle dysfunction is associated with human aging. Studies in animal models have reported morphological changes consistent with denervation in laryngeal muscles with age. Life-long laryngeal muscle activity relies on cytoskeletal integrity and nerve-muscle communication at the neuromuscular junction (NMJ). It is thought that neurotrophins enhance neuromuscular transmission by increasing neurotransmitter release. We hypothesized that treatment with neurotrophin 4 (NTF4) would modify the morphology and functional innervation of aging rat laryngeal muscles. Fifty-six Fischer 344xBrown Norway rats (6- and 30-mo age groups) were used to evaluate to determine if NTF4, given systemically (n = 32) or directly (n = 24), would improve the morphology and functional innervation of aging rat thyroarytenoid muscles. Results demonstrate the ability of rat laryngeal muscles to remodel in response to neurotrophin application. Changes were demonstrated in fiber size, glycolytic capacity, mitochondrial, tyrosine kinase receptors (Trk), NMJ content, and denervation in aging rat thyroarytenoid muscles. This study suggests that growth factors may have therapeutic potential to ameliorate aging-related laryngeal muscle dysfunction.

Functional and genomic changes in the mouse ocular motor system in response to light deprivation from birth.

Previous studies have suggested that abnormal visual experience early in life induces ocular motor abnormalities. The purpose of this study was to determine how visual deprivation alters the function and gene expression profile of the ocular motor system in mice. We measured the effect of dark rearing on eye movements, gene expression in the oculomotor nucleus, and contractility of isolated extraocular muscles. In vivo eye movement recordings showed decreased gains for optokinetic and vestibulo-ocular reflexes, confirming an effect of dark rearing on overall ocular motor function. Saccade peak velocities were preserved, however, arguing that the quantitative changes in these reflexes were not secondary to limitations in force generation. Using microarrays and quantitative PCR, we found that dark rearing shifted the oculomotor nucleus transcriptome to a state of delayed/arrested development. The expression of 132 genes was altered by dark rearing; these genes fit in various functional categories (signal transduction, transcription/translation control, metabolism, synaptic function, cytoskeleton), and some were known to be associated with neuronal development and plasticity. Extraocular muscle contractility was impaired by dark rearing to a greater extent than expected from the in vivo ocular motility studies: changes included decreased force and shortening speed and evidence of abnormal excitability. The results indicate that normal development of the mouse ocular motor system and its muscles requires visual experience. The transcriptional pattern of arrested development may indicate that vision is required to establish the adult pattern, but it also may represent the plastic response of oculomotor nuclei to abnormal extraocular muscles.

Mitochondria are fast Ca2+ sinks in rat extraocular muscles: a novel regulatory influence on contractile function and metabolism.

PURPOSE: The ultrafast extraocular muscles necessitate tight regulation of free cytosolic Ca2+ concentration ([Ca2+]i). Mitochondrial Ca2+ influx may be fast enough for this role. In the present study, three hypotheses were tested: (1) Mitochondrial Ca2+ uptake regulates [Ca2+]i and production of force in extraocular muscle; (2) mitochondrial content correlates with their use as Ca2+ sinks; and (3) mitochondrial content in extraocular muscle is determined by the transcription factors and coactivators that initiate muscle adaptation to aerobic exercise. METHODS: Extraocular and extensor digitorum longus (EDL) muscles from adult Sprague-Dawley rats were used to examine how the Ca2+ release agonists caffeine and 4-chloro-3-ethylphenol (CEP), calcimycin (a Ca2+ ionophore) and carbonyl cyanide m-chlorophenyl hydrazone (CCCP; a mitochondrial uncoupler) alter [Ca2+]i and force transients. Mitochondrial volume density and capillary density were analyzed by stereology and citrate synthase and cytochrome c oxidase by biochemical assays. Real-time PCR measured mRNAs of genes involved in mitochondrial biogenesis. RESULTS: Caffeine, CEP, and calcimycin increased resting [Ca2+]i to a greater extent in EDL. Peak tetanic [Ca2+]i increased in extraocular muscle with caffeine and CEP. CCCP augmented peak tetanic and submaximum [Ca2+]i and force significantly more in extraocular muscles. Mitochondrial volume density and capillary density were three times greater, and citrate synthase and cytochrome c oxidase were only approximately 2-fold higher in extraocular muscle. Calcineurin Aalpha, calcineurin B, and peroxisome proliferator activated receptor (PPAR)gamma were more abundant in extraocular muscle. CONCLUSIONS: These data support the hypothesis that mitochondria serve as Ca2+ sinks in extraocular muscles. The high mitochondrial content of these muscles may partly reflect this additional function. It is likely that mitochondrial Ca2+ influx increases the dynamic response range of the extraocular muscles and matches metabolic demand to supply.

Eliminating the Ant1 isoform produces a mouse with CPEO pathology but normal ocular motility.

PURPOSE: The adenine nucleotide transporter 1 gene (ANT1) encodes an inner mitochondrial membrane protein that transports ATP into the cell. Mutations within ANT1 produce a syndrome of chronic progressive external ophthalmoplegia (CPEO) in humans. Ant1 knockout (Ant1-/-) mice develop cardiomyopathy and mitochondrial myopathy of limb muscles. Because the extraocular muscles (EOM) are preferentially affected in human CPEO, the objective of this study was to determine whether Ant1-/- mice also exhibit an EOM mitochondrial myopathy. METHODS: ANT isoform expression of isolated EOMs, EOM morphology and mitochondrial content, mitochondrial structure and function, ocular motility in intact mice, and contractile performance in isolated muscle preparations were examined. RESULTS: Ant1-/- EOMs had the typical appearance of mitochondrial myopathy, including increase in mitochondrial size, number, and oxidative phosphorylation (OXPHOS) staining. However, there were no measurable ocular motor abnormalities in intact Ant1-/- mice, and their isolated EOMs did not show evidence of increased fatigability. EOMs of wild-type mice exhibited higher levels of Ant2 mRNA compared with hindlimb muscle, which may compensate for the Ant1 loss in mutant mouse EOMs and account for the normal EOM function. CONCLUSIONS: The Ant1-/- mice provide a model in which to study CPEO pathology and compensatory mechanisms.