American Journal of Physiology - Regulatory Integrative and Comparative Physiology
1522-1490
0363-6119
Mỹ
Cơ quản chủ quản: AMER PHYSIOLOGICAL SOC , American Physiological Society
Lĩnh vực:
PhysiologyPhysiology (medical)
Các bài báo tiêu biểu
Inflammatory processes in muscle injury and repair Modified muscle use or injury can produce a stereotypic inflammatory response in which neutrophils rapidly invade, followed by macrophages. This inflammatory response coincides with muscle repair, regeneration, and growth, which involve activation and proliferation of satellite cells, followed by their terminal differentiation. Recent investigations have begun to explore the relationship between inflammatory cell functions and skeletal muscle injury and repair by using genetically modified animal models, antibody depletions of specific inflammatory cell populations, or expression profiling of inflamed muscle after injury. These studies have contributed to a complex picture in which inflammatory cells promote both injury and repair, through the combined actions of free radicals, growth factors, and chemokines. In this review, recent discoveries concerning the interactions between skeletal muscle and inflammatory cells are presented. New findings clearly show a role for neutrophils in promoting muscle damage soon after muscle injury or modified use. No direct evidence is yet available to show that neutrophils play a beneficial role in muscle repair or regeneration. Macrophages have also been shown capable of promoting muscle damage in vivo and in vitro through the release of free radicals, although other findings indicate that they may also play a role in muscle repair and regeneration through growth factors and cytokine-mediated signaling. However, this role for macrophages in muscle regeneration is still not definitive; other cells present in muscle can also produce the potentially regenerative factors, and it remains to be proven whether macrophage-derived factors are essential for muscle repair or regeneration in vivo. New evidence also shows that muscle cells can release positive and negative regulators of inflammatory cell invasion, and thereby play an active role in modulating the inflammatory process. In particular, muscle-derived nitric oxide can inhibit inflammatory cell invasion of healthy muscle and protect muscle from lysis by inflammatory cells in vivo and in vitro. On the other hand, muscle-derived cytokines can signal for inflammatory cell invasion, at least in vitro. The immediate challenge for advancing our current understanding of the relationships between muscle and inflammatory cells during muscle injury and repair is to place what has been learned in vitro into the complex and dynamic in vivo environment.
Tập 288 Số 2 - Trang R345-R353 - 2005
Biochemistry of exercise-induced metabolic acidosis The development of acidosis during intense exercise has traditionally been explained by the increased production of lactic acid, causing the release of a proton and the formation of the acid salt sodium lactate. On the basis of this explanation, if the rate of lactate production is high enough, the cellular proton buffering capacity can be exceeded, resulting in a decrease in cellular pH. These biochemical events have been termed lactic acidosis. The lactic acidosis of exercise has been a classic explanation of the biochemistry of acidosis for more than 80 years. This belief has led to the interpretation that lactate production causes acidosis and, in turn, that increased lactate production is one of the several causes of muscle fatigue during intense exercise. This review presents clear evidence that there is no biochemical support for lactate production causing acidosis. Lactate production retards, not causes, acidosis. Similarly, there is a wealth of research evidence to show that acidosis is caused by reactions other than lactate production. Every time ATP is broken down to ADP and Pi , a proton is released. When the ATP demand of muscle contraction is met by mitochondrial respiration, there is no proton accumulation in the cell, as protons are used by the mitochondria for oxidative phosphorylation and to maintain the proton gradient in the intermembranous space. It is only when the exercise intensity increases beyond steady state that there is a need for greater reliance on ATP regeneration from glycolysis and the phosphagen system. The ATP that is supplied from these nonmitochondrial sources and is eventually used to fuel muscle contraction increases proton release and causes the acidosis of intense exercise. Lactate production increases under these cellular conditions to prevent pyruvate accumulation and supply the NAD+ needed for phase 2 of glycolysis. Thus increased lactate production coincides with cellular acidosis and remains a good indirect marker for cell metabolic conditions that induce metabolic acidosis. If muscle did not produce lactate, acidosis and muscle fatigue would occur more quickly and exercise performance would be severely impaired.
Tập 287 Số 3 - Trang R502-R516 - 2004
Vascular NAD(P)H oxidases: specific features, expression, and regulation The importance of reactive oxygen species (ROS) in vascular physiology and pathology is becoming increasingly evident. All cell types in the vascular wall produce ROS derived from superoxide-generating protein complexes similar to the leukocyte NADPH oxidase. Specific features of the vascular enzymes include constitutive and inducible activities, substrate specificity, and intracellular superoxide production. Most phagocyte enzyme subunits are found in vascular cells, including the catalytic gp91phox (aka, nox2), which was the earliest member of the newly discovered nox family. However, smooth muscle frequently expresses nox1 rather than gp91phox, and nox4 is additionally present in all cell types. In cell culture, agonists increase ROS production by activating multiple signals, including protein kinase C and Rac, and by upregulating oxidase subunits. The oxidases are also upregulated in vascular disease and are involved in the development of atherosclerosis and a significant part of angiotensin II-induced hypertension, possibly via nox1 and nox4. Likewise, enhanced vascular oxidase activity is associated with diabetes. Therefore, members of this enzyme family appear to be important in vascular biology and disease and constitute promising targets for future therapeutic interventions.
Tập 285 Số 2 - Trang R277-R297 - 2003
Whole tissue hydrogen sulfide concentrations are orders of magnitude lower than presently accepted values Hydrogen sulfide is gaining acceptance as an endogenously produced modulator of tissue function. The present paradigm of H2 S (diprotonated, gaseous form of hydrogen sulfide) as a tissue messenger consists of H2 S being released from the desulfhydration of l-cysteine at a rate sufficient to maintain whole tissue hydrogen sulfide concentrations of 30 μM to >100 μM, and these tissue concentrations serve a messenger function. Utilizing physiological concentrations of l-cysteine and aerobic conditions, we found that catabolism of hydrogen sulfide by mouse liver and brain homogenates exceeded the rate of enzymatic release of this compound such that measureable hydrogen sulfide release was less with tissue-containing vs. tissue-free buffers. Analyses of the gas space over rapidly homogenized mouse brain and liver indicated that in situ tissue hydrogen sulfide concentrations were only about 15 nM. Human alveolar air measurements indicated negligible free H2 S concentrations in blood. We conclude rapid tissue catabolism of hydrogen sulfide maintains whole tissue brain and liver concentrations of free hydrogen sulfide that are three orders of magnitude less than conventionally accepted values and only 1/5,000 of the hydrogen sulfide concentration (100 μM) required to alter cellular function in vitro. For hydrogen sulfide to serve as an endogenously produced messenger, tissue production and catabolism must result in intracellular microenvironments with a sufficiently high hydrogen sulfide concentration to activate a local signaling mechanism, while whole tissue concentrations remain very low.
Tập 295 Số 5 - Trang R1479-R1485 - 2008
Central nervous system effects of caffeine and adenosine on fatigue Caffeine ingestion can delay fatigue during exercise, but the mechanisms remain elusive. This study was designed to test the hypothesis that blockade of central nervous system (CNS) adenosine receptors may explain the beneficial effect of caffeine on fatigue. Initial experiments were done to confirm an effect of CNS caffeine and/or the adenosine A1 /A2 receptor agonist 5′- N-ethylcarboxamidoadenosine (NECA) on spontaneous locomotor activity. Thirty minutes before measurement of spontaneous activity or treadmill running, male rats received caffeine, NECA, caffeine plus NECA, or vehicle during four sessions separated by ∼1 wk. CNS caffeine and NECA (intracerebroventricular) were associated with increased and decreased spontaneous activity, respectively, but caffeine plus NECA did not block the reduction induced by NECA. CNS caffeine also increased run time to fatigue by 60% and NECA reduced it by 68% vs. vehicle. However, unlike the effects on spontaneous activity, pretreatment with caffeine was effective in blocking the decrease in run time by NECA. No differences were found after peripheral (intraperitoneal) drug administration. Results suggest that caffeine can delay fatigue through CNS mechanisms, at least in part by blocking adenosine receptors.
Tập 284 Số 2 - Trang R399-R404 - 2003
Quercetin increases brain and muscle mitochondrial biogenesis and exercise tolerance Quercetin is one of a broad group of natural polyphenolic flavonoid substances that are being investigated for their widespread health benefits. These benefits have generally been ascribed to its combination of antioxidant and anti-inflammatory activity, but recent in vitro evidence suggests that improved mitochondrial biogenesis could play an important role. In addition, the in vivo effects of quercetin on mitochondrial biogenesis exercise tolerance are unknown. We examined the effects of 7 days of quercetin feedings in mice on markers of mitochondrial biogenesis in skeletal muscle and brain, and on endurance exercise tolerance. Mice were randomly assigned to one of the following three treatment groups: placebo, 12.5 mg/kg quercetin, or 25 mg/kg quercetin. Following 7 days of treatment, mice were killed, and soleus muscle and brain were analyzed for mRNA expression of peroxisome proliferator-activated receptor-γ coactivator (PGC-1α) and sirtuin 1 (SIRT1), and mitochondrial DNA (mtDNA) and cytochrome c. Additional mice underwent a treadmill performance run to fatigue or were placed in voluntary activity wheel cages, and their voluntary activity (distance, time, and peak speed) was recorded. Quercetin increased mRNA expression of PGC-1α and SIRT1 ( P < 0.05), mtDNA ( P < 0.05) and cytochrome c concentration ( P < 0.05). These changes in markers of mitochondrial biogenesis were associated with an increase in both maximal endurance capacity ( P < 0.05) and voluntary wheel-running activity ( P < 0.05). These benefits of querectin on fitness without exercise training may have important implications for enhancement of athletic and military performance and may also extend to prevention and/or treatment of chronic diseases.
Tập 296 Số 4 - Trang R1071-R1077 - 2009
Free radical biology and medicine: it's a gas, man! We review gases that can affect oxidative stress and that themselves may be radicals. We discuss O2 toxicity, invoking superoxide, hydrogen peroxide, and the hydroxyl radical. We also discuss superoxide dismutase (SOD) and both ground-state, triplet oxygen (3 O2 ), and the more energetic, reactive singlet oxygen (1 O2 ). Nitric oxide (· NO) is a free radical with cell signaling functions. Besides its role as a vasorelaxant,· NO and related species have other functions. Other endogenously produced gases include carbon monoxide (CO), carbon dioxide (CO2 ), and hydrogen sulfide (H2 S). Like· NO, these species impact free radical biochemistry. The coordinated regulation of these species suggests that they all are used in cell signaling. Nitric oxide, nitrogen dioxide, and the carbonate radical (CO3 ·− ) react selectively at moderate rates with nonradicals, but react fast with a second radical. These reactions establish “cross talk” between reactive oxygen (ROS) and reactive nitrogen species (RNS). Some of these species can react to produce nitrated proteins and nitrolipids. It has been suggested that ozone is formed in vivo. However, the biomarkers that were used to probe for ozone reactions may be formed by non-ozone-dependent reactions. We discuss this fascinating problem in the section on ozone. Very low levels of ROS or RNS may be mitogenic, but very high levels cause an oxidative stress that can result in growth arrest (transient or permanent), apoptosis, or necrosis. Between these extremes, many of the gasses discussed in this review will induce transient adaptive responses in gene expression that enable cells and tissues to survive. Such adaptive mechanisms are thought to be of evolutionary importance.
Tập 291 Số 3 - Trang R491-R511 - 2006
Sympathetic and cardiovascular actions of orexins in conscious rats The novel hypothalamic peptides orexin-A and orexin-B are known to induce feeding behavior when administered intracerebroventricularly, but little is known about other physiological functions. The renal sympathetic nerves play important roles in the homeostasis of body fluids and the circulatory system. We examined the effects of intracerebroventricularly administered orexins on mean arterial pressure (MAP), heart rate (HR), renal sympathetic nerve activity (RSNA), and plasma catecholamine in conscious rats. Orexin-A (0.3, 3.0 nmol) provoked an increase in MAP (94.3 ± 0.7 to 101.9 ± 0.7 mmHg and 93.1 ± 1.1 to 108.3 ± 0.8 mmHg, respectively) and RSNA (28.0 ± 7.0 and 57.9 ± 12.3%, respectively). Similarly, orexin-B (0.3, 3.0 nmol) increased MAP (93.9 ± 0.9 to 97.9 ± 0.9 mmHg and 94.5 ± 1.1 to 105.3 ± 1.7 mmHg, respectively). Orexin-A and -B at 3.0 nmol also increased HR. In other conscious rats, a high dose of orexin-A and -B increased plasma norepinephrine. Plasma epinephrine only increased with a high dose of orexin-A. These results indicate that central orexins regulate sympathetic nerve activity and affect cardiovascular functions.
Tập 277 Số 6 - Trang R1780-R1785 - 1999
Exposure to chronic stress downregulates corticosterone responses to acute stressors We used captive European starlings ( Sturnus vulgaris) to test whether corticosterone responses differed in birds held under normal laboratory conditions or conditions of chronic stress. Surprisingly, both basal corticosterone concentrations and corticosterone responses to acute stress were significantly reduced when birds were chronically stressed. To determine the mechanism underlying this reduced response, animals under both conditions were injected with lactated Ringer’s solution (control), adrenocorticotropin (ACTH), arginine vasotocin (AVT), or dexamethasone (DEX). ACTH increased corticosterone concentrations above stress-induced levels in both cases, although maximum responses were lower in chronically stressed birds. AVT did not augment the corticosterone response under nonchronically stressed conditions, but it did under chronically stressed conditions. DEX reduced maximal corticosterone concentrations in both cases. Neither ovine nor rat corticotropin-releasing factor (CRF) altered normal stress responses. These data indicate that changes in responsiveness of the hypothalamic-pituitary-adrenal axis to ACTH and AVT serve to downregulate corticosterone responses during chronic stress. Furthermore, these data lead to the following hypothesis: ACTH output from the pituitary limits maximum corticosterone concentrations under normal conditions, but reduced AVT release from the hypothalamus regulates lower corticosterone concentrations under chronic stress conditions.
Tập 288 Số 6 - Trang R1628-R1636 - 2005
NF-κB mediates the protein loss induced by TNF-α in differentiated skeletal muscle myotubes Nuclear factor-κB (NF-κB) regulates the transcription of a variety of genes involved in immune responses, cell growth, and cell death. However, the role of NF-κB in muscle biology is poorly understood. We recently reported that tumor necrosis factor-α (TNF-α) rapidly activates NF-κB in differentiated skeletal muscle myotubes and that TNF-α acts directly on the muscle cell to induce protein degradation. In the present study, we ask whether NF-κB mediates the protein loss induced by TNF-α. We addressed this problem by creating stable, transdominant negative muscle cell lines. C2C12 myoblasts were transfected with viral plasmid constructs that induce overexpression of mutant I-κBα proteins that are insensitive to degradation via the ubiquitin-proteasome pathway. These mutant proteins selectively inhibit NF-κB activation. We found that differentiated myotubes transfected with the empty viral vector (controls) underwent a drop in total protein content and in fast-type myosin heavy-chain content during 72 h of exposure to TNF-α. In contrast, total protein and fast-type myosin heavy-chain levels were unaltered by TNF-α in the transdominant negative cell lines. TNF-α did not induce apoptosis in any cell line, as assessed by DNA ladder and annexin V assays. These data indicate that NF-κB is an essential mediator of TNF-α-induced catabolism in differentiated muscle cells.
Tập 279 Số 4 - Trang R1165-R1170 - 2000