Mitochondria regulate critical components of cellular function via ATP production, reactive oxygen species production, Ca2+ handling and apoptotic signaling. Two classical methods exist to study mitochondrial function of skeletal muscles: isolated mitochondria and permeabilized myofibers. Whereas mitochondrial isolation removes a portion of the mitochondria from their cellular environment, myofiber permeabilization preserves mitochondrial morphology and functional interactions with other intracellular components. Despite this, isolated mitochondria remain the most commonly used method to infer in vivo mitochondrial function. In this study, we directly compared measures of several key aspects of mitochondrial function in both isolated mitochondria and permeabilized myofibers of rat gastrocnemius muscle. Here we show that mitochondrial isolation i) induced fragmented organelle morphology; ii) dramatically sensitized the permeability transition pore sensitivity to a Ca2+ challenge; iii) differentially altered mitochondrial respiration depending upon the respiratory conditions; and iv) dramatically increased H2O2 production. These alterations are qualitatively similar to the changes in mitochondrial structure and function observed in vivo after cellular stress-induced mitochondrial fragmentation, but are generally of much greater magnitude. Furthermore, mitochondrial isolation markedly altered electron transport chain protein stoichiometry. Collectively, our results demonstrate that isolated mitochondria possess functional characteristics that differ fundamentally from those of intact mitochondria in permeabilized myofibers. Our work and that of others underscores the importance of studying mitochondrial function in tissue preparations where mitochondrial structure is preserved and all mitochondria are represented.

SummaryMitochondria regulate cellular bioenergetics and apoptosis and have been implicated in aging. However, it remains unclear whether age-related loss of muscle mass, known as sarcopenia, is associated with abnormal mitochondrial function. Two technically different approaches have mainly been used to measure mitochondrial function: isolated mitochondria and permeabilized myofiber bundles, but the reliability of these measures in the context of sarcopenia has not been systematically assessed before. A key difference between these approaches is that contrary to isolated mitochondria, permeabilized bundles contain the totality of fiber mitochondria where normal mitochondrial morphology and intracellular interactions are preserved. Using the gastrocnemius muscle from young adult and senescent rats, we show marked effects of aging on three primary indices of mitochondrial function (respiration, H 2 O 2 emission, sensitivity of permeability transition pore to Ca 2+ ) when measured in isolated mitochondria, but to a much lesser degree when measured in permeabilized bundles. Our results clearly demonstrate that mitochondrial isolation procedures typically employed to study aged muscles expose functional impairments not seen in situ. We conclude that aging is associated with more modest changes in mitochondrial function in sarcopenic muscle than suggested previously from isolated organelle studies.

A simple point score of historical features distinguishes vasovagal syncope from syncope of other causes with very high sensitivity and specificity.

A simple point score of historical features distinguishes syncope from seizures with very high sensitivity and specificity.

SummaryTo determine whether mitochondrial dysfunction is causally related to muscle atrophy with aging, we examined respiratory capacity, H 2 O 2 emission, and function of the mitochondrial permeability transition pore (mPTP) in permeabilized myofibers prepared from four rat muscles that span a range of fiber type and degree of age-related atrophy. Muscle atrophy with aging was greatest in fast-twitch gastrocnemius (Gas) muscle ()38%), intermediate in both the fast-twitch extensor digitorum longus (EDL) and slow-twitch soleus (Sol) muscles ()21%), and non-existent in adductor longus (AL) muscle (+47%). In contrast, indices of mitochondrial dysfunction did not correspond to this differential degree of atrophy. Specifically, despite higher protein expression for oxidative phosphorylation (oxphos) system in fast Gas and EDL, state III respiratory capacity per myofiber wet weight was unchanged with aging, whereas the slow Sol showed proportional decreases in oxphos protein, citrate synthase activity, and state III respiration. Free radical leak (H 2 O 2 emission per O 2 flux) under state III respiration was higher with aging in the fast Gas, whereas state II free radical leak was higher in the slow AL. Only the fast muscles had impaired mPTP function with aging, with lower mitochondrial calcium retention capacity in EDL and shorter time to mPTP opening in Gas and EDL. Collectively, our results underscore that the age-related changes in muscle mitochondrial function depend largely upon fiber type and are unrelated to the severity of muscle atrophy, suggesting that intrinsic changes in mitochondrial function are unlikely to be causally involved in aging muscle atrophy.

Background Vasovagal syncope (VVS) patients have a reduced health‐related quality of life (HRQoL). There are limited data comparing HRQoL and psychological profile in VVS patients and healthy individuals. We tested the hypothesis that VVS patients have greater impairment in both HRQoL and psychological profile compared to healthy nonfainting individuals, and that both outcome measures are negatively correlated for VVS patients. Methods The RAND 36‐Item Health Survey (RAND36), global health visual analogue scale (VAS), Hospital Anxiety and Depression Scale, Anxiety Sensitivity Index, and Positive and Negative Affect Schedule – Expanded Form were completed by healthy individuals and at baseline by VVS patients enrolled in the Second Prevention of Syncope Trial, a randomized, placebo‐controlled trial of fludrocortisone for VVS. Results Data were available on 76 VVS patients (34 ± 14 years; 68% F) and 85 healthy participants (35 ± 11 years; 80% F). Compared to healthy participants, VVS patients reported poorer HRQoL on all scales of the RAND36 and the VAS. VVS patients had significantly greater anxiety, depression, and anxiety sensitivity (each P < 0.001). VVS patients had more negative affect (P < 0.001) and less positive affect (P = 0.003) compared to healthy participants. Anxiety, depression, and anxiety sensitivity were negatively correlated with HRQoL for VVS patients, but not for healthy participants. Conclusion In this first direct comparison, VVS patients have a significantly reduced HRQoL and more anxiety and depression compared to healthy nonfainting individuals. For VVS patients, there is a relationship between psychological distress and HRQoL, suggesting a potential benefit from more comprehensive assessment and treatment.

The most common age at which vasovagal syncope first presents is 13 years, and patients remain at risk of syncope for many years. Lifelong coping strategies may be desirable.

Metoprolol was not effective in preventing vasovagal syncope in the study population.