bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanosensory activation of the somatosensory cortex in unanesthetized rats
Authors: Chan Pei‐Ying Sarah , Hotchkiss Mark , Adams Sherry , Davenport Paul W
Published: June 2021

Respiratory related evoked potentials (RREP) elicited by inspiratory mechanical loads have been demonstrated in humans and lambs. However, it was unknown if an occlusion paradigm can also elicit a RREP in chronically instrumented, awake, spontaneously breathing rats. Rats were instrumented with electrodes on the surface of the cortex and an occluder was sutured around the trachea. After recovery, the tracheal cuff was inflated for 3 to 5 breaths. Occlusions were presented approximately every 30 seconds for approximately 10 to 18 minutes. Occlusion‐elicited evoked potentials (EP) were obtained by computer‐signal averaging the ECoG activity. A short‐latency peak was observed on the averaged occlusion‐elicited evoked potentials in all animals for Day 1 and 2. A long‐latency peak was observed in all animals from Day 3 to 11. The result demonstrated that inspiratory occlusion elicits an evoked potential in the cortex of awake, spontaneously breathing rats. The waveform of the EP changes with chronic occlusion conditioning.
The acetazolamide analogue N‐methyl acetazolamide does not alter the ventilatory response to hypoxia but reduces the hypercapnic response in the anesthetized cat
Authors: Teppema Luc J , Dahan Albert , Swenson Erik R
Published: June 2021

Acetazolamide (AZ) may have cardiorespiratory effects independently from inhibition of carbonic anhydrase (CA). In contrast to methazolamide, it impairs respiratory muscle function in rabbits and reduces the hypoxic ventilatory response in cats. In rat pulmonary arterial smooth muscle cells, AZ inhibits the hypoxia‐induced rise in [Ca2+]i, an effect that is shared by N‐methyl acetazolamide (NMA), an AZ analogue devoid of inhibiting effects on CA. We have studied the effect of NMA on the ventilatory response to hypoxia and hypercapnia in 7 anesthetized cats. NMA, (20 mg.kg−1, i.v.) did not influence the hypoxic response measured at a constant end‐tidal PCO2 of about 6 kPa, described with the exponential equation Vi (inspired ventilation) = G.{(exp) − DPO2} + R, with G = hypoxic sensitivity, D = shape factor and R = ventilation in hyperoxia. Mean values of G, D and R were not different in control and following NMA. Surprisingly however, the ventilatory CO2 response curve described with Vi = S(PCO2−B) with the CO2 sensitivity S and the extrapolated X‐intercept (apneic threshold) B underwent dramatic changes: S and B decreased by 60 and 72%, respectively. Whether these effects of NMA may be due to vascular effects remains to be examined.
Estradiol in carotid bodies impairs the ventilatory acclimatization to hypoxia in Epo overexpressing female mice
Authors: Soliz Jorge , Joseph Vincent , Gassmann Max
Published: June 2021

Erythropoietin (Epo) impacts the ventilatory response to acute hypoxia in a sex‐dependent manner, with female mice having better capability to cope with reduced oxygenation. Here we hypothesized that ventilatory acclimatization to chronic hypoxia (VAH) in transgenic female mice showing high levels of Epo in brain and blood (Tg6) will be improved compared to WT animals. The data obtained by plethysmography showed the opposite: VAH was blunted in Tg6 female mice. To define whether this phenomenon had central and/or peripheral origin, a bilateral chemodenervation was performed. This procedure allowed testing the central response in absence of carotid body information. Interestingly, chemodenervated Tg6 and WT female mice had similar VAH, thus suggesting that carotid bodies were responsible for the blunted response. Accordingly, the sensitivity to oxygen alteration in arterial blood (Dejour test) was impaired in Tg6 carotid bodies. As blunted VAH occurred in female but not male Tg6 mice, the involvement of female steroids was suspected. Indeed, estradiol serum level was 4‐folds higher in Tg6 mice compared to WT animals. In addition, ovarectomy decreased VAH in WT animals, but restored VAH in Tg6 female mice, while estradiol treatment in ovarectomiced Tg6 females suppressed VAH. We concluded that under chronic hypoxia, estradiol in carotid bodies blunts the VAH of Tg6 female mice overexpressing Epo.
The hypoxia‐induced facilitation of augmented breaths is prevented by the common action of carbonic anhydrase inhibitors
Authors: Bell Harold James , Haouzi Philippe A.
Published: June 2021

Hypoxia facilitates the generation of augmented breaths (ABs) in the breathing rhythm. Acetazolamide (Atz) treatment prevents this facilitation, likely by promoting CO2 retention and counteracting hyperventilation‐induced alkalosis. However, Atz is also known to decrease the sensitivity of the arterial chemoreceptors. The question therefore remains as to whether Atz prevents the facilitation of ABs during hypoxia by offsetting the effects of respiratory alkalosis, or by suppressing peripheral chemoreceptor activity. In this study, we addressed this question by examining the effects of an alternative carbonic anhydrase inhibitor, methazolamide (Mtz), which has been reported to leave peripheral chemoreceptor sensitivity intact. Respiratory variables were monitored before, during and after two days of Mtz treatment (10 mg/kg i.p., bid) in unsedated and unrestrained adult male rats. Pre‐treatment, the number of ABs observed in a 5 minute observation window was 1.2 ± 0.8 and 17.4 ± 3.8 in room air and hypoxia, respectively. During Mtz treatment, the facilitation of ABs in hypoxia was rapidly and reversibly suppressed such that ABs we no longer significantly more frequent than they were in room air. The present results demonstrate that the hypoxia‐induced facilitation of ABs can be suppressed via the general effects of carbonic anhydrase inhibition, which are common to both Atz and Mtz.
Central/Peripheral Chemoreceptor Interaction in the Unanesthetized Dog: Evidence for Hyperaddition
Authors: Blain Gregory , Smith Curtis , Henderson Kathleen , Dempsey Jerome
Published: June 2021

We assessed the contribution of carotid body chemoreceptors (CB) to the ventilatory response to specific CNS hypercapnia in the unanesthetized awake dog. We used extracorporeal blood perfusion of the reversibly isolated carotid sinus to maintain normal blood gases (normoxic, normocapnic perfusate) at the CB, to inhibit the CB (hyperoxic, hypocapnic perfusate), or to stimulate the CB (hypoxic, normocapnic perfusate) while the systemic circulation, and therefore the central nervous system (CNS), was exposed to normocapnia and 4 progressive levels of hypercapnia for 7 minutes at each level. Relative to control (normoxic and normocapnic perfusion), we found that CB inhibition decreased the slope of the ventilatory response to CNS hypercapnia in all dogs by 80% on average (N=6) whereas CB stimulation increased the slope of the ventilatory response to CNS hypercapnia in all dogs by 123% on average (N=4). We conclude that the gain of the CNS CO2/H+ chemoreceptors is critically dependent on CB afferent activity and the CNS/CB interaction results in hyperadditive ventilatory responses. Supported by NIH/NHLBI & American Heart Association.
Differential regulation of ventral spinal atypical PKC and ERK MAP kinase following hypocapnia‐induced respiratory neural inactivity
Authors: Broytman Oleg , Strey Kristi A , Baker‐Herman Tracy L
Published: June 2021

Hypocapnia‐induced respiratory neural inactivity elicits mechanisms of plasticity that enhance phrenic motor output once activity is restored, an effect known as inactivity‐induced phrenic motor facilitation (iPMF). Since atypical protein kinase C (aPKC) activity is necessary for iPMF, we tested the hypothesis that iPMF is associated with increased aPKC expression in spinal regions associated with the phrenic motor nucleus. Anesthetized and ventilated rats were exposed to 30 min of hypocapnia (5–10 mmHg below baseline) to reversibly stop respiratory neural activity. Following hypocapnia, ventral C3–C5 was fractionated into membrane‐enriched, cytoplasm‐enriched and nucleus‐enriched fractions. Total and phosphorylated aPKC increased in membrane‐enriched (47 +/− 10 and 39 +/− 11%, respectively, p<0.05), but decreased in cytoplasm‐enriched fractions (−77 +/− 5 and −74 +/− 6%, respectively, p<0.05) post‐hypocapnia. In contrast, there were no significant changes in membrane or cytoplasmic expression of phosphorylated ERK (−41 +/− 14 and −12 +/− 10%, respectively, p>0.05), a kinase implicated in other forms of spinal plasticity. Phospho‐ERK was increased in nuclear fractions post‐hypocapnia (97 +/− 17%, p<0.05), suggesting a possible role for ERK in longer‐lasting forms of plasticity elicited by neural inactivity. These data support a prominant role for aPKC in iPMF following hypocapnia (NIH HL69064).
Erythropoietin (EPO)‐induced phrenic motor facilitation (PMF) requires ERK activation
Authors: Dale‐Nagle Erica Arden , Satriotomo Irawan , Mitchell Gordon S
Published: June 2021

Although EPO is well known for its role in hematopoiesis, it is also a potent neuronal growth/trophic factor. We recently demonstrated that cervical spinal EPO receptor activation elicits long‐lasting PMF (Dale‐Nagle and Mitchell, 2009). Here, we test the hypotheses that: 1) EPO and EPO receptors are expressed in phrenic motor neurons; and 2) that extracellular regulated kinase (ERK) MAP kinase activation is necessary for EPO‐induced PMF since EPO receptors signal via ERK. Immunohistochemistry revealed both EPO and EPO receptor protein within presumptive motor neurons in the C4 ventral horn. Integrated phrenic nerve activity was recorded in anesthetized and ventilated rats prepared with intrathecal catheters at C4. Rats were injected with vehicle (10μl; 0.1% BSA in aCSF; n=1), rhEPO (10μl; 10–30IU, n=7), the MEK inhibitor U0126 (12μl; 100μM) 15 min prior to EPO (10μl, 20 IU; n=3), or U0126 alone (12μl; n=1). EPO induced PMF for at least 90 minutes post‐injection (75% ± 12% baseline; p<0.05 vs. vehicle). U0126 abolished EPO‐induced PMF (13% ± 13%; n.s.) and U0126 alone had no effect on phrenic nerve activity (7.9%; n.s.). This is the first demonstration that EPO receptors are expressed in respiratory motor neurons, and that EPO‐induced spinal plasticity is ERK‐dependent. Further investigations are necessary to understand the important role of EPO in respiratory neuroplasticity (NIH NS05777 & HL80209).
Enhanced phrenic but not XII long‐term facilitation (LTF) following acute intermittent hypoxia (AIH) in a rat model of amyotrophic lateral sclerosis (ALS)
Authors: Nichols Nicole L. , Mitchell Gordon S.
Published: June 2021

Despite significant phrenic (~80%) and intercostal motor neuron loss (~65%), ventilation is preserved until late in disease progression in a rat model of ALS (SOD1G93A). Thus, mechanisms of plasticity offset loss of respiratory motor neurons. In contrast, hypoglossal (XII) motor neurons are spared until endstage. We tested the hypothesis that plasticity is enhanced during disease progression in phrenic (not XII) motor output. In anesthetized, paralyzed and ventilated rats, phrenic and XII motor output were assessed after AIH (3, 5‐minute bouts of 11% O2) and compared with time control experiments. AIH‐induced phrenic LTF (pLTF) and XII LTF were studied in ALS rats at 90 and 130 days of age, and at end stage (20% decrease in mass), which were compared to age‐matched, wild‐type litter mates. At days 90 and 130, pLTF and XII LTF were similar in mutant and wild‐type rats and were significantly greater than time controls (p < 0.001). At endstage, pLTF was significantly greater in mutant vs. wild type rats 60 min post‐AIH (106±24%, n=7; vs. 42±8%, n=10, respectively; p < 0.001). XII LTF did not differ between mutant and wild type rats at end‐stage (93±24%, n=8; vs. 73±19%, n=12, respectively). Thus, phrenic (but not XII) motor output exhibits meta‐plasticity during motor neuron disease. Enhanced pLTF may arise from increased expression of molecules necessary for pLTF in normal rats, and may preserve ventilation in ALS.
Advice for Submitting Manuscripts to Scientific Journals
Authors: Albertine Kurt
Published: June 2021

What makes a manuscript enticing to scientific journals and readers of the journals? An important element is that the science in the manuscript advances the field. Authors should clearly state how their study's results advance the field. To do so requires composing a story that is easy to read, easy to understand, and does not require the reader to figure out what the authors mean. Writing should focus on precise word choice, concise and well‐constructed sentences and paragraphs. Al way to meet these goals is to compose the hypothesis or question, outline the methods and results sections, and prepare the figures and tables. Figures and tables should be presented in readable and understandable, uniform format that adheres to the “Instructions to Authors” for the journal to which the manuscript will be submitted. The discussion section places the major results in the context of the field, and considers some of the study's limitation the drafted methods, results, and discussion sections provide boundaries that limit the introduction and abstract sections, and title. By so doing, an enticing, informative, understandable story will arrive on the editorial office's manuscript submission web site.
Choosing Your Journal Wisely
Authors: Schoenwolf Gary
Published: June 2021

How does an author select the journal for their latest paper submission? This question is the focus of the first part of the talk. A good strategy is to select the highest impact journal in your field that is also a good fit for your paper: that is, a journal in which the topic of your paper will be of high interest to its readers. Selecting such a journal will showcase your work in the field, assuming that your paper is ultimately accepted by the journal for publication. This leads to the focus of the second part of the talk, which is how to prepare your paper and how to communicate with editors/reviewers to maximize the chances that your paper will be accepted. The main topic discussed in this part of the talk include "selling" your manuscript by using presubmission inquires, focused cover letters, informative and interesting titles, and abstracts, introductions, and discussions that clearly state the importance of your study and the hypothesis tested, question answered, or problem solved.
Getting Published: Peer Review and Manuscript Management
Authors: Carey John C
Published: June 2021

The process of modern scientific publication is a multi‐faceted and complex enterprise. The system‐really a culture‐comprises the collaboration and partnership of editors and their editorial offices with publishers and their production team. The "customers" ‐the benefactors‐ are the scientific community, the authors, and the multitude of reviewers who commit‐based mostly on academic citizenship and a trust in the process‐ to provide evidence‐based critiques of the article submissions. Indeed editorial peer review (PR)is the centerpiece of the enterprise. My presentation includes 2 goals: to describe the operational process of manuscript mangement and to highlight recent advances in our knowledge of PR. The learner will ideally be able to summarize this recent emerging body of literature on PR and the strengths, limitations, and misconceptions of the process.
Cardiolipin and Its Redox Interactions With Cytochrome c In Apoptosis
Authors: Kagan Valerian E.
Published: June 2021

During apoptosis cytochrome c (cyt c) interacts with cardiolipin (CL) and obtains a new catalytic function as a CL‐specific peroxidase that causes oxidation of CL in mitochondria. Fatty acid hydroperoxides are ~1,000 times more effective as sources of oxidizing equivalents for the peroxidase function of cyt c/CL than H2O2. Migration of CL from the inner to the outer mitochondrial membrane is a pre‐requisite for its interaction with cyt c. Thus, CL acts as a redox switch that turns off the electron transporting function of cyt c and turns on its peroxidase activity. Mitochondria‐targeted inhibitors of CL peroxidation act as potent anti‐apoptotic agents thus offering new opportunities for drug discovery. In the cytosol, released cyt c interacts with another anionic phospholipid, phosphatidylserine (PS), and catalyzes its oxidation. Peroxidation facilitates PS externalization ‐ essential for the recognition and clearance of apoptotic cells by macrophages.
Targeted single point mutation of NaV1.4 in mouse increases sodium influx and potassium‐induced force depression in EDL and soleus muscle
Authors: Lucas Brooke , Khogali Shiemaa , Hayward Lawrence , Renaud Jean‐Marc
Published: June 2021

The single point mutation M1592V on the human skeletal muscle sodium channel, NaV1.4, causes Hyperkalemic Periodic Paralysis (HyperKPP). HyperKPP is associated with greater sodium influx and sensitivity to the potassium depressing effect on force. The objective of this study was to determine if introducing a missense substitution corresponding to a human familial HyperKPP mutation (Met1592Val) into the mouse gene (mice(+/M1592V)) encoding the skeletal muscle voltage‐gated Na+ channel NaV1.4 also results in greater sodium flux and potassium sensitivity. EDL and soleus muscles were exposed to either 4.7 mM (control) or 9–10 mM K+ while measuring either 22Na+ uptake or peak tetanic force. 22Na+ uptake was 3‐times greater in EDL and soleus muscles of mice(+/M1592V) when compared to the uptake in wild type muscles. The drop in peak tetanic force at 9–10 mM was much greater in EDL and soleus muscles of mice(+/M1592V) than in wild type muscles. Furthermore, adding 1–2 nM TTX, to partially block sodium channels, caused a decrease in peak tetanic force in wild type muscles but produced an increase in force in EDL and soleus muscles of mice(+/M1592V). However, the peak tetanic force of muscle(+/M1592V) in the presence of TTX was still less than that observed in wild type muscles. We conclude that the introduction of the M1592V mutation in the mouse genome increases sodium influx and the K+ sensitivity of skeletal muscle as observed in human suffering of HyperKPP. However, partially blocking Na+ channels with TTX failed to return the force back to the level observed in wild type muscles, which suggests that an increased intracellular sodium also contributes to the reduced force.
Experimental investigation of thermal effects in skeletal muscle: tetanic and post‐tetanic potentiation
Authors: Barnes William Stephen
Published: June 2021

Force production in striated muscle is influenced by temperature, as are most physiological processes. The purpose of this investigation was to determine what effect altering incubation temperature might have on force output before and after brief periods of tetanic stimulation. Sartorii muscles (60–70 mg) from R. pipiens were dissected‐free and vertically‐mounted in water‐jacketed chambers containing oxygenated (100%), Ringer solution (pH 7.2; 20°C). To determine peak twitch tension (PT, g) at different temperatures (10°–30°C), muscles were stimulated via supramaximal square wave pulses (0.2 ms) every 10 s for 2 min before and after a 2.5 s tetanic contraction (80 Hz). Averaged PT immediately preceding tetanic stimulation was 25.2 ± 2.7, 18.1 ± 2.2 and 14.1 ± 0.9 at 10°C, 20°C and 30°C, respectively. Corresponding thermal ratios (R10) were 0.72 (10°–20°C) and 0.78 (20°–30°C). Peak tetanic tensions (PTT, g) and tension‐time integrals (TTI, g·s) were 47.3 ± 4.7, 60.1 ± 6.5, and 49.4 ± 5.8, and 100.9 ± 6.8, 140.4 ± 17.0 and 107.4 ±16.1 at 10°C, 20°C and 30°C, respectively. Averaged PT immediately following tetanic stimulation was 27.2 ± 2.1, 25.1 ± 0.7, and 15.4 ± 0.6 at 10°C, 20°C and 30°C, respectively. R10 values were 0.92 (10°–20°C) and 0.61 (20°–30°C). These results suggest that variations in the thermal environment may significantly mediate force output and alter the efficacy of neuro‐motor control mechanisms.
Early recovery from large‐strain lengthening contractions is not compromised in dysferlin‐null skeletal muscle
Authors: Roche Joseph A , Ru Lisa W , Bloch Robert J
Published: June 2021

The recovery of dysferlin‐null skeletal muscles from injurious large‐strain lengthening contractions is delayed due to extensive necrosis and inflammation that peaks 3 days after injury. Here we test the hypothesis that muscles of dysferlin‐null A/J mice and control A/WySnJ mice recover during the first few hours after large‐strain injury, but that A/J muscle subsequently undergoes secondary damage leading to a loss of contractile torque.

METHODS

We studied the response to injury from 15 large‐strain lengthening contractions in the tibialis anterior muscle of A/J and A/WySnJ mice. We measured contractile torque and assessed morphological changes in muscle ~ 10 min and 3, 6, 12, 24, 48 and 72 hrs after injury.

RESULTS

Changes in torque and counts of necrotic fibers after injury are shown in Table 1 (*, p<0.05 A/W Vs A/J; †, p<0.05 compared to 3 hrs).

Contractile torque and counts of necrotic fibers after injury

Mouse
Uninjured
~ 10 min
3 hrs
6 hrs
12 hrs
24 hrs
48 hrs
72 hrs

Torque (% Pre‐injury) Mean ± S.D.
A/WySnJ
100
62 ± 2
87 ± 2
92 ± 5
85 ± 10
89 ± 5
85 ± 5
95 ± 6

A/J
100
66 ± 4
78 ± 7
75 ± 0*
70 ± 5*
70 ± 5*
62 ± 1*†
64 ± 9*†

Necrotic fibers(% total # fibers counted) Mean ± S.D.
A/WySnJ
0.2 ± 0.5
1 ± 2
2 ± 1
2 ± 1
2 ± 3
3 ± 2
3 ± 4
2 ± 2

A/J
1 ± 1
2 ± 2
7 ± 4*
9 ± 6*
8 ± 4*
18 ± 14*†
19 ± 9*†
23 ± 8*†

CONCLUSIONS

Dysferlin‐null muscle recovers as well as control by 3 hrs following injury, after which it gradually loses contractile torque and necrotic fibers appear.

This work was funded by the Jain Foundation Inc.
Exercise limitation, muscle atrophy and increased angiopoietin mRNA in a mouse model of pulmonary TNFa induced inflammation
Authors: Tang Kechun , Wagner Peter D , Breen Ellen C
Published: June 2021

Many chronic inflammatory diseases exhibit high circulating TNFa and skeletal muscle weakness. In this study, a mouse model of chronic pulmonary inflammation due to SP‐C driven TNFa overexpression was used to evaluate the effects of systemic TNFa on exercise capacity and locomotor skeletal muscle expression of atrophy and angiogenic genes. SP‐C/TNFa (+/−) mice (female, 6–8 months of age) had a 5.7‐fold increase in serum TNFa levels compared to littermate controls (29.6±9.6 vs. 5.2±3.5 pg/ml, p<0.001), reduced body weight (25.9±3.3 vs. 32.0±4.6 g, p=0.028, n=4), soleus mass (7.7±1.2 vs. 9.6±2.2 mg, p=0.021) and treadmill running endurance (60±9 vs. 81±11 min, p=0.016). In the soleus, PGC‐1a mRNA levels, measured by real time RT‐PCR, were decreased in the TNF(+/−) mice compared to control (1.6±0.4 vs. 3.1±1.4 units, p=0.014), and angiopoieitn‐1 mRNA was increased (51.5±15.9 vs. 10.0±6.3 units, p<0.001). These data suggest (1) prolonged high systemic TNFa levels alter skeletal muscle metabolism and function; (2) PGC‐1a, an important metabolic regulator, may be a key factor in inflammation associated muscle atrophy; (3) TNFa regulation of muscle angiopoietin‐1 has a potential role in protecting vascular integrity in chronic systemic inflammatory conditions.

NIH/NHLBI 1 P01 HL091830‐01A1
Regulatory volume increase in single mouse soleus muscle fibres assessed simultaneously using intracellular fluorescence and fibre width
Authors: Lindinger Michael I , Leung Matt , Moynes Jaclyn , Shortreed Karin E , Hawke Thomas J
Published: June 2021

Mammalian skeletal muscle cells have the ability to regulate volume in response to increases or decreases in extracellular osmolarity. In the present study we measured the time course of change in single fibre intracellular calcein fluorescence (volume indicastor) and width in response to varied 200 mosmol/L increase in extracellular osmolarity using NaCl or sucrose. Adult mouse EDL single fibres were isolated using collagenase and incubated in DMEM prior to and during experimentation. Fibres were loaded with calcein‐AM for 30 min, and triple‐rinsed with calcein‐free DMEM. After obtaining baseline images NaCl or sucrose solution was added. Fibre images were obtained at 3–6 s intervals for up to 60 min. Fibre images were analyzed for intensity and width at 2–3 sites. Increased osmolarity resulted in a rapid increase in fibre fluorescence and decrease in fibre width. Both variables gradually recovered to baseline values within ~45 min. Bumetanide, an inhibitor of the sodium‐potassium‐2 chloride cotransporter (NKCC) impaired recovery. There was a linear relationship between increases in fibre fluorescent intensity and decreases in fibre width. It is concluded that the NKCC is involved in regulatory volume increase in skeletal muscle, and that changes in fluorescence intensity can be used as an indicator of changes in cell volume.

Supported by NSERC of Canada.
Nitric oxide prevents calcium‐induced calpain proteolysis and atrophy in L6 myotubes
Authors: Zeanah Elizabeth Henderson , Soltow Quinlyn A. , Criswell David S.
Published: June 2021

Skeletal muscle atrophy can occur as a result of disuse, disease, or aging. Mechanistic pathways among these conditions vary, but in most cases, levels of intracellular calcium (IC Ca2+) increase. This rise in IC Ca2+ stimulates calpain activity and subsequent protein degradation. Calpains cleave the structural proteins that hold the sarcomere together, thereby releasing the contractile proteins for proteasome degradation; this is thought to be the rate‐limiting step in skeletal muscle proteolysis. Little is known about the regulation of calpain activity, but nitric oxide (NO) has been proposed as a possible mediator. This study used the Ca2+ ionophore calcimycin to increase IC Ca2+ and to induce calpain activity in L6 myotubes. We hypothesized that treatment with an NO donor would attenuate calpain proteolysis and myotube atrophy in a dose‐dependent manner following treatment with calcimycin. Results show an attenuation of calpain‐specific talin proteolysis with 1 μM and 10 μM PAPA‐NO after 60 minutes of calcimycin treatment, and preliminary data show prevention of myotube atrophy with DETA‐NO after 24–48 hours of calcimycin treatment. Therefore, moderate doses of NO can prevent calpain proteolysis and possibly skeletal muscle atrophy following a Ca2+ challenge in L6 myotubes. This study was funded by the American Heart Association.
Effects of Temperature on Low‐Frequency Fatigue in Isolated Skeletal Muscle
Authors: Barnes William Stephen
Published: June 2021

Muscles exposed to sustained, low‐frequency stimulation experience a reduction in force production known as low‐frequency fatigue. Also, many aspects of the contractile process in skeletal muscle are influenced by ambient temperature. The purpose of this study was to investigate what interactions might exist between variations in temperature and this form of muscle impairment. Paired sartorii muscles (60–70 mg) from male R. pipiens (N=10) were dissected‐free and vertically‐mounted in water‐jacketed chambers containing oxygenated (100%), Ringer solution (pH 7.2). Both muscles from a single animal were stimulated identically for 20s (supramaximal square wave pulses; 0.2 ms; 25 Hz) albeit at two different temperatures (15°C and 25°C). Peak tensions (PT, g; means ± SEM) were 35.0 ± 2.4 (15°C) v. 23.2 ± 1.8 (25°C). Average tensions (AT, g) were 12.9 ± 2.1 (15°C) and 8.0 ± 0.7 (25°C). Tension‐time integrals (TTI, g·s) were 234.6 ± 30.5(15°C) and 145.8 ± 14.8 (25°C). In each instance, differences between 15°C and 25°C were highly significant (p<.01). Nevertheless, the total percent decline in force over the stimulation period did not appear to be greatly influenced by ambient temperature (−86.4 ± 0.9% (15°C) v. −89.3 ± 0.7% (25°C; p>.01). Results suggest that variations in the thermal environment may have a somewhat lesser effect on relative fatigue in skeletal muscle when compared to other indices of muscle function.
Doxorubicin stimulates catabolism in C2C12 myotubes
Authors: Gilliam Laura A. A. , Moylan Jennifer S. , Patterson Elaine W. , Wilson Anne S. , Reid Michael B.
Published: June 2021

Doxorubicin, a commonly prescribed chemotherapeutic agent, causes skeletal muscle wasting in cancer patients undergoing chemotherapy. Previous studies in mice show that the E3 ubiquitin ligase, MAFbx/atrogin‐1 is upregulated in skeletal muscle following doxorubicin administration, an effect regulated by p38 MAPK signaling. Activation of p38 MAPK also promotes caspase‐3 activation. These findings led us to hypothesize that doxorubicin causes skeletal muscle atrophy through p38 MAPK signaling, leading to the upregulation of MAFbx/atrogin‐1 and caspase‐3. We measured the loss of myofibrillar proteins in C2C12 myotubes exposed to doxorubicin (0.2 μM, 48 hrs). Compared to control, actin (mean ± SE; −49 ± 4 %, n=3, p<0.01) and myosin (−40 ± 9 %, n=11, p<0.05) proteins decreased. p38 MAPK phosphorylation was elevated in 30 mins following doxorubicin exposure (16 ± 3 %, n=6, p<0.05). Doxorubicin increased MAFbx/atrogin‐1 mRNA 16 hrs (74 ± 8%, n=3, p<0.01) and 24 hrs (132 ± 8 %, n=3, p<0.01) following exposure. Caspase‐3, both precursor and active form, were elevated 6 hrs (precursor: 25 ± 7 %, n=3, p<0.05; active: 125 ± 35 %, n=3) and 24 hrs (precursor: 36 ± 6, n=3, p<0.01; active: 87 ± 12 %, n=3, p<0.01) following doxorubicin. Our data shows that doxorubicin causes skeletal muscle protein loss, which may be mediated through p38 MAPK signaling and upregulation of MAFbx/atrogin‐1 and caspase‐3.

Supported by: T32 HL086341‐02 (EWP) and AHA predoctoral fellowship(LAAG)
The time course appearances of isometric contractile properties and muscle‐specific proteins in a novel three‐dimensional skeletal muscle model
Authors: Nakamura Tomohiro , Yamasaki Kenichi , Fujisato Toshia
Published: June 2021

C2C12 cells were embedded in type‐I collagen gel solution at density of 1.0 × 107 cells/ml. The suspension was added to two artificial tendons(elastase treated porcine aorta). The medium was cultured for 2 days in growth medium and shifted to differentiation medium supplemented with 7% horse serum. The contraction force (F), the change ratio of contraction (dF/dt) and the change ratio of relaxation (dF/drt) were assessed at 7,14,21 days after onset of cultivation. The protein accumulation in myosin heavy chain (MHC) and electron micrograph (EM) were also assessed at 7,14,21 days after cultivation.

Up to 14 days, F, dF/dt and dF/drt increased dramatically. In addition, the protein accumulations of α‐actin, fast and slow MHC also increased markedly. From 14 days to 21 days, F, dF/dt, dF/drt increased gradually, however, the protein accumulations of α‐actin, fast and slow MHC did not show remarkable change. At 21 days, the sarcomere structures and basal lamina were evident by EM.

These results suggest that the appearances of contractile properties do not quite correspond to the appearances of muscle‐specific protein at latter stage in maturation of three‐dimensional skeletal muscle cells.
Circadian rhythm of spontaneous activity and body temperature and its relationship with exercise capacity
Authors: Machado Frederico Sander Mansur , Rodovalho Gisele Veira , Coimbra Cândido Celso
Published: June 2021

The aim of this study was to verify relationships between circadian spontaneous activity and body temperature (Tb) with exercise capacity in two different phases of light/dark cycle.

Circadian activity and Tb of Wistar rats (n=11), under regular environmental conditions with free access to water and food, were continuously recorded using a telemetric sensor (G2 E‐Mitter) chronically implanted (ip) 3 days before. We accessed total time to fatigue, workload and Tb during exercise. Animals were submitted to progressive exercise test protocols until fatigue during the early light and dark phases. Each test was separated for 3 days. Fatigue was set as the moment when rats couldn't keep pace with treadmill.

Results suggest increased circadian dark phase activity compared to light phase (p<0.01). This was accompanied by greater light phase exercise capacity and Tb variance and heat accumulation (p<0.05). There was no direct relationship of circadian activity and exercise capacity although at light phase a specific negative relationship of circadian temperature and exercise capacity was observed (r=−0.74, p<0.01).

We demonstrated that circadian activity was not directly related to exercise capacity, despite the difference regarding exercise capacity and thermoregulation at two different circadian periods of rat activity.

Supported by: CNPq and FAPEMIG
Pathological vascular stiffness in mice with disrupted circadian rhythm
Authors: Anea Ciprian , Ali Mohammed Irfan , Osmond Jessica , Stepp David W. , Rudic Dan
Published: June 2021

The transcription factor Bmal1 is an integral component of the molecular machinery that drives circadian rhythm. Previously, we have described that mice with disruption of Bmal1 (Bmal1‐KO) exhibit pathological remodeling and enhanced vascular injury. Herein, we undertook studies to examine both large artery and resistance artery compliance in these mice with dysfunctional circadian clocks. After inducing arterial remodeling by ligation of the common carotid artery, high resolution ultrasound imaging was implemented in vivo in live, anesthetized mice, to reveal dilatation, impaired remodeling, and increased vascular stiffness in the arteries undergoing remodeling of Bmal1‐KO mice. Furthermore, vascular compliance of naïve, unligated resistance vessels (third order branches of the femoral artery) was reduced in Bmal1‐KO mice. As matrix metalloproteinases (MMPs) represent key elements involved in the turnover of the extracellular matrix and vascular stiffness, we assessed MMP activity and expression in arteries of Bmal1‐KO mice. Bmal1‐KO mice exhibited an increase in MMP activity and expression in naïve vessels, an effect which was further exacerbated in remodeled vessels. These data suggest that circadian clock regulation of extracellular matrix turnover may be an important factor in the progression to hardening of arteries during vascular disease.
Is rapid vasodilation in response to single contractions impaired in human obesity?
Authors: Harrell John , Blain Gregory , Limberg Jacqueline , Mortensen Garrett , Schrage William
Published: June 2021

Mechanical factors associated with muscle contraction may influence vascular responses to exercise. We tested the hypothesis that rapid vasodilation in response to single dynamic forearm contractions would be reduced in young obese adults (n=14, BMI 37±1) when compared to lean controls (n=15, BMI 21±1). We measured heart rate (ECG), blood pressure (BP, arm cuff & Finapress), and forearm blood flow (FBF, Doppler ultrasound) during a single forearm contraction (performed in triplicate) at 15, 30, and 50% of forearm maximal voluntary contraction (MVC). To account for higher BP in obese subjects, we assessed forearm vascular conductance (FVC=FBF/BP). Regardless of differences in baseline FVC, a given % change in FVC from baseline (%ΔFVC) will reflect the same % change in vessel radius (ie vasodilation). Therefore, we compared %ΔFVC between groups at each intensity. At rest, FVC was higher in obese (p<0.05). With contraction, the %ΔFVC was intensity‐dependent (50%>30%>15%) and peaked within 4–6 cardiac cycles after contraction in both groups. The %ΔFVC was similar at 15% between groups, but significantly lower in obese subjects at 30 and 50% MVC (p<0.05). These results indicate that with increasing intensity, obese adults exhibit reduced rapid vasodilation in response to a single dynamic forearm contraction. Research Support: NIH HL091397 and AHA 0815622G
Randomized Controlled Trial Using Resistance Training to Improve Arterial Function in Overweight, Young Adult Males
Authors: Croymans Daniel M , Krell Shannon L , Roberts Christian K
Published: June 2021

Controversy exists regarding the effects of resistance training (RT) on arterial stiffness. We are investigating the effects of RT on vascular function in sedentary, overweight, young adult males, and report data from the first 12 subjects (age 22.8±1.8 yrs, BMI 32.2±3.1 kg/m2). Subjects were randomized in a 3:1 fashion to an RT group (12 wks of training at 3 d/wk) or a control group (C). After an overnight fast and abstaining from exercise for 72 hrs, subjects were assessed for changes in body weight (BW), BMI, waist circumference (WC), body composition by dual energy X‐ray absorptiometry, 1‐repetition maximum (1‐RM) strength, carotid‐femoral pulse wave velocity (cfPWV), augmentation index (AIx), aortic pressure (AP), and sub‐endocardial viability ratio (SEVR). Preliminary analyses compared changes in the RT (n=8) and C (n=4) groups pre‐ and post‐intervention. No significant changes in BMI, WC, BW, total fat mass, AIx, AP, and SEVR were noted. However, the RT group had a significant increase in lean body mass (LBM) and 1‐RM strength for leg press, chest press and seated row, compared to C (all p<0.03). There was a trend towards a decrease in cfPWV in the RT group (RT: pre 7.1±0.8 vs. post 6.9±1.3, C: 6.6±0.2 vs. 7.5±0.6, p=0.14). Preliminary results indicate an increase in LBM, strength, and a trend towards an improvement in arterial stiffness with a periodized RT intervention, even in the face of no changes in BW, BMI, or WC. American Heart Association BGIA #0765139Y.
Post‐exercise hypotension: The effect of water drinking during exercise
Authors: Fukuba Yoshiyuki , Kajimoto Chie , Yamada Masako , Koga Shunsaku , Endo Masako Y
Published: June 2021

There is commonly a sustained reduction in mean arterial blood pressure (MAP) after a prolonged exercise, even in normotensive individuals, i.e., post‐exercise hypotension (PEH). Since the lowered pre‐load is supposed to be one of the potential causes of PEH, due to the decreased plasma volume (PV) via dehydration during exercise, we aimed to explore the effect of water drinking to PEH. Nine male subjects undertook 60‐min leg cycle ergometer exercise at work rate of 60 % of heart rate (HR) reserve without (C protocol) or with (W protocol) oral water intake, followed by 30‐min of supine rest. Subjects remained at supine rest for a further 60‐min. In the W protocol, the subjects were able to drink the water with an ad‐lib manner (~600 ml) during exercise to adjust the exercise‐induced reduction of body weight. The HR, MAP, and relative change (Δ) of PV were measured throughout the protocol. The MAP in C protocol was substantially reduced during recovery (~5 mmHg; p<0.05), compared to pre‐exercise level. In contrast, MAP in W protocol did not show the substantial reduction during recovery, and was significantly higher to those in C protocol. The ΔPV was not different during recovery between both protocols. These results indicate that PEH seems unlikely to be association to the factor related to the PV change, while oral water intake per se has an unsolved influence to post‐exercise MAP.

(Support: JSPS‐KAKENHI, 20700526, 21370111)
Effects of regular endurance exercise on brachial blood flow response to mental stress
Authors: Komine Hidehiko , Takai Yohei , Akazawa Nobuhiko , Maeda Seiji , Yoshizawa Mutsuko , Sugawara Jun , Yokoi Takashi
Published: June 2021

Muscle vasodilator response to mental stress is partly mediated by nitric oxide (NO). Regular endurance exercise augments NO‐mediated endothelium‐dependent vasodilator function. We therefore tested the hypothesis that regular endurance exercise augments NO‐mediated endothelium‐dependent vasodilator function, and thereby enhances muscle blood flow response to mental stress. To examine this hypothesis, we measured brachial blood flow response to 3 min of mental arithmetic using Doppler ultrasound in sedentary and endurance trained young men. To assess NO‐mediated endothelium‐dependent vasodilator function, we measured flow‐mediated vasodilatation (FMD) of the brachial artery using ultrasound imaging. Brachial blood flow was increased during mental arithmetic both in the sedentary and the endurance trained group, but the increase in blood flow was less in the trained group. FMD of the brachial artery did not differ between the groups. These results suggest that regular endurance exercise in young men blunts brachial blood flow response to mental arithmetic, which is irrespective of endothelium‐dependent vasodilator function of the brachial artery.
Intra‐individual Reproducibility of Hyperemic Responses to Ischemic Exercise
Authors: Lopez Marcos G. , Casey Darren P. , Silva Bruno M. , Walker Branton G. , Joyner Michael J.
Published: June 2021

We examined the reproducibility of the hyperemic response to ischemic exercise (IE) in the forearm and compared the magnitude of this response to ischemia alone (reactive hyperemia, RH). Eight subjects (6M/2F; 26 ±1 yrs) performed 3 trials of IE and 2 of RH. IE consisted of 5 min of forearm ischemia with rhythmic forearm exercise (20% of max) during the final 2 min. RH consisted of 5 min of forearm ischemia. Peak and total (area under the curve) forearm blood flow (FBF; venous occlusion plethysmography) and blood pressure (MAP; Finometer) were measured for 3 min after each stimulus. Forearm vascular conductance (FVC; ml/100ml/min/mmHg) was calculated from FBF (ml/100ml/min) and MAP (mmHg). The mean intra‐individual coefficient of variation (CV) across the 3 IE trials was 13.0±1.4% and 16.3±1.2% for baseline‐adjusted peak FBF and FVC, respectively. The CVs for total FBF and FVC were 10.4±1.0% and 14.9±1.0%, respectively. Mean peak FBF was greater for IE compared to RH (37.3±2.7 and 30.0±1.3, P < 0.002), however mean peak FVC was not different (35.1±2.6 and 34.5±1.1, P = 0.80). Mean total FBF (67.6±3.9 and 18.0±2.5, P < 0.001) and mean total FVC (64.7±2.7 and 20.8±3.2, P < 0.001) were greater for IE compared to RH, respectively. Thus, our data suggest that the hyperemic response to IE is reproducible, and that the magnitude of this response is greater than that of ischemia alone.

NIH HL‐46493 (MJJ), CTSA RR‐024150 and RR‐024152
Effect of mouse strain on mitochondrial biogenesis and exercise
Authors: Davis Greggory Ryan , Wang Pingyun , Hwang Paul M
Published: June 2021

Sponsor: Jacqueline M. Stephens

Purpose

Improvement in exercise capacity and change in mitochondrial DNA (mtDNA) were examined in B6 mice compared to wild‐type p53 and heterozygous FVB mice.

Methods

FVB and B6 mice performed a high‐intensity five‐week treadmill exercise protocol. Maximal exercise testing was performed on all groups and time was recorded at the point of exhaustion. All groups were rested for 72 hours prior to dissection to minimize any acute effects of exercise. Body fat percentage was determined and the gastrocnemius and soleus muscles were harvested and analyzed.

Results

The FVB strain nearly doubled work capacity and had a significantly lower body fat percentage compared to the B6 strain. mtDNA copy number did not change significantly in either strain and it actually decreased in the trained FVB p53 +/+ and p53 +/− groups.

Conclusions

FVB mice demonstrated both a greater intrinsic exercise capacity as well as a greater response to exercise training while variation in the genotype of the FVB mice did not significantly affect response to exercise. The greater exercise capacity seen in the FVB mice may be due to a number of other factors including cardiovascular, biomechanical, and psychological aspects. It is also possible that exercise capacity may have increased due to genes mediated by nuclear DNA, making change in mtDNA more difficult to detect.

National Heart, Lung, and Blood Institute. National Institutes of Health, Bethesda, MD 20892
Fiber Type‐Dependent Suppression of Myocellular Anabolic Response in the Obese Zucker Rat
Authors: Nilsson Mats Inge , Dobson Justin P , Greene Nicholas P , Cummins C Brooke , McHenry Elaina , Cloud Whitney M , Wiggs Michael P , Biehl Adam J , Fluckey James D
Published: June 2021

The purpose of this study was to determine if insulin resistance syndrome is associated with a blunted myocellular anabolic response (e.g., cumulative protein synthesis rates [24‐h FSR]) following high‐intensity resistance exercise (RE). Lean (Fa/?) and obese (fa/fa) 5‐mo‐old male Zucker rats engaged in 4 sessions of lower body RE and were enriched with 2H2O to assess cumulative FSR in red (RG) and white gastrocnemius (WG). Obese Zucker rats exhibited a significantly higher basal 24‐h FSR in RG (+22%, P = 0.006) and WG (+ 38%, P = 0.026) compared to the lean phenotype, but were unable to augment protein synthesis rates in WG (−7%, P > 0.05) to the same extent as lean rats (+34%, P = 0.027) following RE. Contrary to previous research, mixed muscle protein synthesis rates are enhanced rather than suppressed in selected muscle groups of the obese Zucker rat. Insulin resistance syndrome may impair the myocellular anabolic response following high‐intensity RE.
Strenuous Exercise Enhances Thrombin Generation Induced by Platelet‐derived Microparticles
Authors: Wang Jong‐Shyan , Chen Yu‐Wen
Published: June 2021

This investigation elucidates how strenuous exercise affects platelet‐derived microparticles (PDMP) with procoagulant factors and PDMP‐mediated thrombin generation (TG) under pathological high (HS, 100 dyne/cm2) shear stress by closely examining 24 sedentary men who exercised strenuously (up to VO2max) on a bicycle ergometer. The PDMP/platelets with procoagulant factors and the dynamic TG in plasma were measured using two‐color flow cytometry and a calibrated, automated thrombinography, respectively. The results showed that HS increased the levels of total PDMP and the PDMP binding procoagulant factor V/Va (FV/Va) or VIII (FVIII), expressing tissue factor (TF), or exposing phosphatidylserine (PS), which were accompanied by elevated the height of thrombin peak and increased the rate of TG in PDMP‐rich plasma. Moreover, the HS simultaneously enhanced the binding of FV/Va or FVIII to platelets and the exposure of PS on platelets. Under the HS condition, strenuous exercise increased the counts of FV/Va‐/FVIII‐/TF‐rich PDMP and PS‐exposed PDMP and augmented PDMP‐promoted peak height and rate of TG, whereas the ability to binding of FV/Va or FVIII to platelets and the extent of PS exposure on platelets were enhanced following this exercise. Therefore, we conclude that strenuous exercise enhances shear‐induced TG by increased the release of procoagulant‐rich microparticles from platelets.
Muscular Efficiency in Highly‐Trained Type 1 Diabetic Subjects
Authors: Cassuto Nicholas A. , Wong Eric C. , Baldi James C. , Wheatley Courtney M. , Foxx‐Lupo William T. , Snyder Eric M.
Published: June 2021

Type 1 diabetes (T1DM) is associated with impaired vascular function and ability of the muscle to utilize glycogen as a fuel source. We examined muscle efficiency (ME) during exercise between 12 highly‐trained T1DM subjects and 10 matched healthy subjects (age=33±8 vs. 40±8yrs, ht.=180±11 vs. 181±9cm, weight=74±11 vs. 74±9kg, VO2peak=123±19 v 126±22% pred., for healthy and T1DM, mean±SD). We measured power output and VO2 across the groups during 4 workloads (wkld 1=79±13 vs. 78±13watts, relative work=33±4 vs. 32±4%peak, VO2=1610±272 vs. 1670±354ml/kg/min; wkld 2=119±19 vs. 116±20watts, relative work=49±7 vs. 47±6%peak, VO2=1976±270 vs. 2015±363ml/kg/min; wkld 3=158±26 vs. 155±27watts: relative work=66±9 vs. 63±7%peak, VO2=2417±417 vs. 2383±397ml/kg/min; and wkld 4=198±32 vs. 193±34watts, relative work=82±11 v 78±9%peak, VO2=2794±490 vs. 2628±537ml/kg/min, for healthy and T1DM). ME was higher in T1DM (ME 1= 20.8±3.2 vs. 27.2±8.3, ME 2 = 22.7±2.4 vs. 26.7±6.4, ME 3 = 23.3±2.8 vs. 26.6±4.3, ME 4 = 24.0±2.6 vs. 28.5±3.5, for healthy and type 1 diabetics). Change in ME was then calculated (Δeff 1=43.3±25.9 vs. 101.1±157.9%, Δeff 2=39.8±38.4 vs. 27.0±4.8%, Δeff 3=38.8±48.4 vs. 30.1±9.7%, Δeff 4=29.1±7.7 vs. 43.8±24.4%). These results suggest that highly‐trained T1DM subjects demonstrate a higher ME during exercise, possibly due to differences in substrate utilization between these groups.