Search

Purpose: The molecular factors targeted by androgens and estrogens on muscle mass are not fully understood. The current study aimed to explore gene and protein expression of Atrogin-1, MuRF1, and myostatin in an androgen deprivation-induced muscle atrophy model. Methods: We examined the effects of Orx either with or without testosterone (T) or estradiol (E) administration on Atrogin-1 gene expression, and MuRF1 and myostatin gene and protein expression. Measurements were made in soleus (SOL), extensor digitorum longus (EDL) and levator ani/bulbocavernosus (LA/BC) of male C57BL/6 mice. Results: Thirty days of Orx resulted in a reduction in weight gain and muscle mass. These effects were prevented by T. In LA/BC, Atrogin-1 and MuRF1 mRNA was increased throughout 30 days of Orx, which was fully reversed by T and partially by E administration. In EDL and SOL, a less pronounced upregulation of both genes was only detectable at the early stages of Orx. Myostatin mRNA levels were downregulated in LA/BC and upregulated in EDL following Orx. T, but not E, reversed these effects. No changes in protein levels of MuRF1 and myostatin were found in EDL at any time point following Orx. Conclusions: The atrophy in SOL and EDL in response to androgen deprivation, and its restoration by T, is accompanied by only minimal changes in atrogenes and myostatin gene expression. The marked differences in muscle atrophy and atrogene and myostatin mRNA between LA/BC and the locomotor muscles suggest that the murine LA/BC is not an optimal model to study Orx-induced muscle atrophy. [ABSTRACT FROM AUTHOR]

The influence of inhibiting the inward rectifier and Na/K pump on endothelium-dependent hyperpolarizations in smooth muscle cells of the mesenteric artery was investigated. Membrane potential was measured with microelectrodes, and the influence of low concentrations of Ba2+ (30 µM) and of high concentrations of ouabain (0.5 mM) on smooth muscle hyperpolarization elicited by prolonged or by transient exposure to acetylcholine (ACh, 3×10–7 M) was assessed in the continuous presence of NG-nitro-l-arginine (100 µM) and indomethacin (50 µM). Pre-exposure to Ba2+ did not inhibit the magnitude of smooth muscle cell hyperpolarization induced by ACh superfusion, but significantly slowed its onset and time course. The membrane potential response to transient ACh applications, however, was impaired. After combined Ba2+ and ouabain pre-exposure, peak hyperpolarizations to ACh superfusion were somewhat decreased but not abolished. In addition, 4–5 mM increases of the extracellular K+ concentration consistently depolarized smooth muscle cells. These findings argue against the idea that smooth muscle inward rectifier K+ channels and Na/K pumping play a role in the ACh-induced endothelium-dependent hyperpolarization of this preparation. Moreover, the slowing of smooth muscle membrane hyperpolarization by Ba2+ is discussed in terms of the influence of this ion on the release of hyperpolarizing factor. [ABSTRACT FROM AUTHOR]

Endothelium-dependent relaxation effects have been reported to be impaired in thoracic aorta from genetic and experimentally induced hypertensive rats. This study extends these observations to carotid artery and abdominal aorta from renovascular hypertensive rats. It was also found that rats with coarctation of aorta show depressed endothelium-dependent relaxation responses in thoracic aorta above the stenosis (high pressure region) while no depressed responses are observed in abdominal aorta below the stenosis (normal pressure region). Reversibility of the depression of endothelium-dependent relaxation was investigated on aorta from renovascular hypertensive rats in which blood pressure was normalized by removal of the stenotic kidney three months after induction of hypertension. Endothelium-dependent responses were restored partially after 1-2 weeks and completely after two months of normalization of blood pressure. These results indicate that the increased blood pressure is indeed the causative factor responsible for the impaired endothelium-dependent relaxations in arteries from experimental hypertensive rats, a phenomenon which is reversible, at least in our experimental conditions. [ABSTRACT FROM AUTHOR]

Objective: To investigate the influences of root canal instrumentation on the load capacity and fracture modes of tooth roots under axial compression by performing mechanical tests and finite element analysis (FEA)., Methods: Thirty bovine incisor roots were trimmed into cylinders of 5.0 mm diameter. They were randomly divided into two groups, one with root canals instrumented to ∼2.0 mm in diameter, and one without instrumentation. The specimens were fractured under uniaxial compression at a crosshead speed of 0.2 mm/min, and then micro-CT was used to reveal the fracture patterns in three dimensions. FEA was further performed, using the extended finite element method (XFEM), to compare the compression-induced stress distributions and the initiation and propagation of root fractures in both groups., Results: The mean fracture load of the non-instrumented group (2334 ± 436 N) was statistically significantly higher than that of the instrumented group (1857 ± 377 N) (p < 0.01). Three types of root fractures were identified according to the path and length of the cracks: end-face crack, partial-length crack, and full-length crack. As to the fracture modes, the incidence of partial-length root fracture was the highest in both groups (60% for the non-instrumented group and 53.3% for the instrumented group), followed by that of full-length fracture (26.7% and 40%, respectively) and then end-face fracture (13.3% and 6.7%, respectively). The percentage of full-length fracture was slightly higher in the instrumented group. FEA showed that the compression induced higher Tresca stresses but lower maximum principal stresses in the canal walls of the instrumented group. The XFEM simulations predicted that the fracture of both groups initiated from the outer root surface near an end face and propagated axially to the middle third of the root and radially towards the root canal. These numerical results agreed well with our experimental findings., Significance: Within the limitation of this study, it was found that root canal instrumentation could significantly decrease the load capacity of tooth roots and potentially increase their susceptibility to full-length root fracture under uniaxial compression., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Aims: Connexins form gap-junctions (GJs) that directly connect cells, thereby coordinating vascular cell function and controlling vessel diameter and blood flow. GJs are composed of two hemichannels contributed by each of the connecting cells. Hemichannels also exist as non-junctional channels that, when open, lead to the entry/loss of ions and the escape of ATP. Here we investigated cross-talk between hemichannels and Ca 2+ /purinergic signalling in controlling blood vessel contraction. We hypothesized that hemichannel Ca 2+  entry and ATP release contributes to smooth muscle cell (SMC) Ca 2+  dynamics, thereby influencing vessel contractility. We applied several peptide modulators of hemichannel function and inhibitors of Ca 2+  and ATP signalling to investigate their influence on SMC Ca 2+  dynamics and vessel contractility., Methods and Results: Confocal Ca 2+  imaging studies on small mesenteric arteries (SMAs) from rat demonstrated that norepinephrine-induced SMC Ca 2+  oscillations were inhibited by blocking IP 3 receptors with xestospongin-C and by interfering with hemichannel function, most notably by the specific Cx43 hemichannel blocking peptide TAT-L2 and by TAT-CT9 that promotes Cx43 hemichannel opening. Evidence for hemichannel involvement in SMC function was supported by the fact that TAT-CT9 significantly increased SMC resting cytoplasmic Ca 2+  concentration, indicating it facilitated Ca 2+  entry, and by the observation that norepinephrine-triggered vessel ATP release was blocked by TAT-L2. Myograph tension measurements on isolated SMAs showed significant inhibition of norepinephrine-triggered contractility by the ATP receptor antagonist suramin, but the strongest effect was observed with TAT-L2 that gave ∼80% inhibition at 37 °C. TAT-L2 inhibition of vessel contraction was significantly reduced in conditional Cx43 knockout animals, indicating the effect was Cx43 hemichannel-dependent. Computational modelling suggested these results could be explained by the opening of a single hemichannel per SMC., Conclusions: These results indicate that Cx43 hemichannels contribute to SMC Ca 2+  dynamics and contractility, by facilitating Ca 2+  entry, ATP release, and purinergic signalling., (Published on behalf of the European Society of Cardiology. All rights reserved. © The Author 2016. For Permissions, please email: journals.permissions@oup.com.)

Key Points: Using recombinant DNA technology, the present study provides the first strong and direct evidence indicating that β-alanine is an efficient substrate for the mammalian transaminating enzymes 4-aminobutyrate-2-oxoglutarate transaminase and alanine-glyoxylate transaminase. The concentration of carnosine and anserine in murine skeletal and heart muscle depends on circulating availability of β-alanine, which is in turn controlled by degradation of β-alanine in liver and kidney. Chronic oral β-alanine supplementation is a popular ergogenic strategy in sports because it can increase the intracellular carnosine concentration and subsequently improve the performance of high-intensity exercises. The present study can partly explain why the β-alanine supplementation protocol is so inefficient, by demonstrating that exogenous β-alanine can be effectively routed toward oxidation., Abstract: The metabolic fate of orally ingested β-alanine is largely unknown. Chronic β-alanine supplementation is becoming increasingly popular for improving high-intensity exercise performance because it is the rate-limiting precursor of the dipeptide carnosine (β-alanyl-l-histidine) in muscle. However, only a small fraction (3-6%) of the ingested β-alanine is used for carnosine synthesis. Thus, the present study aimed to investigate the putative contribution of two β-alanine transamination enzymes, namely 4-aminobutyrate-2-oxoglutarate transaminase (GABA-T) and alanine-glyoxylate transaminase (AGXT2), to the homeostasis of carnosine and its methylated analogue anserine. We found that, when transfected into HEK293T cells, recombinant mouse and human GABA-T and AGXT2 are able to transaminate β-alanine efficiently. The reaction catalysed by GABA-T is inhibited by vigabatrin, whereas both GABA-T and AGXT2 activity is inhibited by aminooxyacetic acid (AOA). Both GABA-T and AGXT2 are highly expressed in the mouse liver and kidney and the administration of the inhibitors effectively reduced their enzyme activity in liver (GABA-T for vigabatrin; GABA-T and AGXT2 for AOA). In vivo, injection of AOA in C57BL/6 mice placed on β-alanine (0.1% w/v in drinking water) for 2 weeks lead to a 3-fold increase in circulating β-alanine levels and to significantly higher levels of carnosine and anserine in skeletal muscle and heart. By contrast, specific inhibition of GABA-T by vigabatrin did not affect carnosine and anserine levels in either tissue. Collectively, these data demonstrate that homeostasis of carnosine and anserine in mammalian skeletal muscle and heart is controlled by circulating β-alanine levels, which are suppressed by hepatic and renal β-alanine transamination upon oral β-alanine intake., (© 2016 The Authors. The Journal of Physiology © 2016 The Physiological Society.)

Introduction: The contribution of reduced testosterone levels to tail suspension (TS)-induced muscle atrophy remains equivocal. The molecular mechanism by which testosterone regulates muscle mass during TS has not been investigated., Methods: Effects of TS on serum testosterone levels, muscle mass, and expression of muscle atrophy- and hypertrophy-inducing targets were measured in soleus (SOL) and extensor digitorum longus (EDL) muscles after testosterone administration during 1, 5, and 14 days of TS in male mice., Results: TS produced an increase followed by a transient drop in testosterone levels. Muscle atrophy was associated with downregulation of Igf1 and upregulation of Mstn, Redd1, Atrogin-1, and MuRF1 mRNA with clear differences in Igf1, Mstn, and MAFbx/Atrogin-1 gene expression between SOL and EDL. Testosterone supplementation did not affect muscle mass or protein expression levels during TS. Conclusions The known anabolic effects of testosterone are not sufficient to ameliorate loss of muscle mass during TS., (© 2014 Wiley Periodicals, Inc.)

Background: Propofol is a short-acting intravenous anesthetic agent. In rare conditions, a life-threatening complication known as propofol infusion syndrome can occur. The pathophysiologic mechanism is still unknown. Some studies suggested that propofol acts as uncoupling agent, others suggested that it inhibits complex I or complex IV, or causes increased oxidation of cytochrome c and cytochrome aa3, or inhibits mitochondrial fatty acid metabolism. Although the exact site of interaction is not known, most hypotheses point to the direction of the mitochondria., Methods: Eight rats were ventilated and sedated with propofol up to 20 h. Sequential biopsy specimens were taken from liver and skeletal muscle and used for determination of respiratory chain activities and propofol concentration. Activities were also measured in skeletal muscle from a patient who died of propofol infusion syndrome., Results: In rats, authors detected a decrease in complex II+III activity starting at low tissue concentration of propofol (20 to 25 µM), further declining at higher concentrations. Before starting anesthesia, the complex II+III/citrate synthase activity ratio in liver was 0.46 (0.25) and in skeletal muscle 0.23 (0.05) (mean [SD]). After 20 h of anesthesia, the ratios declined to 0.17 (0.03) and 0.12 (0.02), respectively. When measured individually, the activities of complexes II and III remained normal. Skeletal muscle from one patient taken in the acute phase of propofol infusion syndrome also shows a selective decrease in complex II+III activity (z-score: -2.96)., Conclusion: Propofol impedes the electron flow through the respiratory chain and coenzyme Q is the main site of interaction with propofol.

Purpose: Enhanced carnosine levels have been shown to be ergogenic for high-intensity exercise performances, although the role of carnosine in the control of muscle function is poorly understood. Therefore, the aim of this study was to investigate the effect of long-term supplementation with increasing doses of carnosine and beta-alanine on muscle carnosine, anserine, and taurine levels and on in vitro contractility and fatigue in mice., Methods: Male Naval Medical Research Institute mice (n = 66) were control fed or supplemented with either carnosine (0.1%, 0.5%, or 1.8%) or beta-alanine (0.6 or 1.2%) in their drinking water for 8-12 wk. Soleus and extensor digitorum longus (EDL) were tested for in vitro contractile properties, and carnosine, anserine, and taurine content were measured in EDL and tibialis anterior by high-performance liquid chromatography., Results: Only supplementation with 1.8% carnosine and 1.2% beta-alanine resulted in markedly higher carnosine (up to +160%) and anserine levels (up to +46%) compared with control mice. Beta-alanine supplementation (1.2%) resulted in increased fatigue resistance in the beginning of the fatigue protocol in soleus (+2%-4%) and a marked leftward shift of the force-frequency relation in EDL (10%-31% higher relative forces)., Conclusion: Comparable with humans, beta-alanine availability seems to be the rate-limiting step for synthesis of muscle histidine-containing dipeptides in mice. Moreover, muscle histidine-containing dipeptides loading in mice moderately and muscle dependently affects excitation-contraction coupling and fatigue.

Cannabinoids have potent vasodilatory actions in a variety of vascular preparations. Their mechanism of action, however, is complex. Apart from acting on vascular smooth muscle or endothelial cannabinoid receptors, several studies point to the activation of type 1 vanilloid (TRPV1) receptors on primary afferent perivascular nerves, stimulating the release of calcitonin gene-related peptide (CGRP). In the present study, the direct influence of the cannabinoid methanandamide and the neuropeptide CGRP on the membrane potassium ion (K(+)) currents of rat mesenteric myocytes was explored. Methanandamide (10 μM) decreased outward K(+) currents, an effect similar to that observed in smooth muscle cells from the rat aorta. Conversely, CGRP (10 nM) significantly increased whole-cell K(+) currents and this effect was abolished by preexposure to tetraethylammonium chloride (1 mM) or iberiotoxin (100 nM), inhibitors of large-conductance calcium-dependent K (BK(Ca)) channels but not by glibenclamide (10 μM), an inhibitor of ATP-dependent K channels. In the presence of the CGRP receptor antagonist CGRP(8-37) (100 nM), the adenylyl cyclase inhibitor SQ22536 (100 μM), or the protein kinase A inhibitor Rp-cAMPS (10 μM), CGRP had no effect. These findings show that methanandamide does not increase membrane K(+) currents in smooth muscle cells of small mesenteric arteries, supporting an indirect mechanism for the reported hyperpolarizing influence in this vessel. Moreover, CGRP acts directly on these smooth muscle cells by increasing BK(Ca) channel activity in a CGRP receptor and cyclic adenosine monophosphate-dependent way. Collectively, these data indicate that methanandamide relaxes and hyperpolarizes intact mesenteric vessels by releasing CGRP from perivascular nerves.