bluuebunny/crossref_metadata_2025_split huggingface dataset:
Distribution and Regulation of Aquaporins in Intestinal Epithelial Cells
Authors: Chow Elaine , MacNaughton Wallace 
Published: June 2021

Sodium absorption and chloride secretion create osmotic gradients that drive water transport across intestinal epithelial cells. Aquaporins (AQP) are tetrameric water‐selective channels that may play an important role in facilitating transcellular water movement and maintaining physiological electrolyte balance. In the kidney, key AQPs are regulated by intracellular cAMP. We hypothesized that the cellular distribution of AQPs in the intestinal epithelium is regulated by cAMP. RT‐PCR of three intestinal epithelial cell lines demonstrated mRNA expression of: AQP1, 2, 3, and 5 in SCBN; AQP1, 2, 3, 5, 7, 8, and 9 in T84; and AQP1, 2, 3, 4, and 5 in CMT. Confocal imaging showed immunoreactivity for AQP1, 2, 3, 4, and 7 in SCBN and AQP1, 4, 6, and 9 in T84. Real time confocal live cell imaging tracked intracellular movement of GFP‐linked human AQP1 gene construct transfected into T84 cells. It suggested an increase in apical fluorescence of AQP1 within 20 min of forskolin (FSK) treatment. Cellular fractionation of CMT whole cell lysate by differential centrifugation showed a significant FSK‐dependent increase in AQP1 protein in the plasma membrane and no FSK‐induced change in the intracellular fraction. This study demonstrates that multiple AQPs are expressed in intestinal epithelial cell lines, and provides evidence for cAMP‐dependent regulation of AQP1 trafficking.Supported by CCFC.
Differential Regulation of FXYD5, FXYD9 and FXYD11 Expression in Atlantic Salmon Gill During Parr‐Smolt Transformation and Sea Water Acclimation
Authors: Tipsmark Christian K , Madsen Steffen S 
Published: June 2021

The Na,K‐ATPase is the major driving force for ion secretion in teleost gill chloride cells. Accordingly, gill enzyme abundance increases and isoform composition changes in response to increased salinity and during the salmon parr‐smolt transformation (PST) prior to seaward migration in the spring. We identified 3 isoforms of the FXYD protein family (FXYD5, FXYD9 and FXYD11) in the salmon gill, which may assist in regulating the catalytic rate of the Na,K‐ATPase in these situations. FXYD proteins are auxiliary subunits which may associate with the alpha‐subunit of the Na,K‐ATPase. Expression in the gill of the 3 isoforms was investigated during PST and acclimation of freshwater (FW) salmon to sea water (SW). During the PST, FXYD5 mRNA levels were unaltered, whereas the expression of FXYD9 and FXYD11 peaked in May, coinciding with optimal SW‐tolerance and peak levels of Na,K‐ATPase of the FW dwelling salmon. Abrupt SW‐transfer induced an increase in Na,K‐ATPase abundance and FXYD5 expression but no overall changes in FXYD9 and FXYD11. The parallel increase in FXYD9 and FXYD11 levels with Na,K‐ATPase abundance during PST but not during SW‐acclimation suggests that these auxillary proteins play a particular role in controlling catalytic rate in situ when the FW fish prepares for SW entry.The research was supported by the Carlsberg Foundation (2005‐1‐311) and the Danish Natural Research Council (272‐06‐0526).
Phorbol ester stimulation enhances endocytosis and ubiquitination of the sodium chloride co‐transporter
Authors: Ko Benjamin , Cooke Leslie L , Hoover Robert S 
Published: June 2021

The sodium chloride co‐transporter (NCC) is the principal salt‐absorptive pathway in the distal convoluted tubule. Recently, we described a novel pathway of NCC regulation in which phorbol esters stimulate Ras guanyl‐releasing protein 1, triggering a cascade ultimately activating ERK1/2 MAPK and decreasing NCC cell surface expression. Surface expression may decrease either by inhibition of forward trafficking or enhanced endocytosis. To investigate the mechanism of altered NCC surface expression in this system, mouse distal convoluted tubule (mDCT) cells were biotinylated at 4ºC, then re‐warmed to 37ºC and treated for 20 minutes with either vehicle (DMSO) or 100nM TPA (phorbol ester). Cells were washed with MesNa to remove any biotin remaining at the cell surface, then lysed. Strepavidin pulldown and immunoblotting showed that after 20 minutes of TPA treatment, the amount of internalized NCC increased by 459±25% compared to control (p<0.01). The ubiquitination of NCC may mediate this process, as TPA stimulation resulted in a 485±33% increase in ubiquitinated NCC as compared to control (p<0.05), measured by immunoprecipitation of NCC followed by immunoblotting for ubiquitin in mDCT cell lysates treated with TPA or vehicle. These data indicate that phorbol ester stimulation of mDCT cells triggers enhanced endocytosis and increased ubiquitination of NCC.This work was supported by a NIH Grant K08 DK070668.
Normotensive menopausal rats: Effects of Enalapril on Sexual Hormones and on Nitric Oxide System Activity in the Kidney, Heart and Aorta
Authors: Zilberman Judith Miriam , Veiras Luciana , Minotti Natalia , Bianciotti Agustina , Villamil Alberto , Costa Maria Angeles , Arranz Cristina 
Published: June 2021

Studies in animal models suggest that sexual hormones, oxidative stress, and impaired nitric oxide (NO) system and renin‐angiotesin system activation play a role in hypertension during menopause. However, the involved mechanisms are still unknown.Objective: To evaluate the effects of enalapril, an inhibitor of the angiotesin‐converting enzyme (ACE), on systolic blood pressure (SBP), sexual hormones and NO syntase (NOS) activity in normotensive menopausal rats.Wistar rats were ovariectomized, and ten weeks later were divided into two groups: Experimental (E) treated with enalapril for 30 days (15 mg/Kg/day) and Control (C) with tap water. We measured: indirect SBP, androgen, estradiol and FSH plasma levels, and NOS activity (14C‐arginine) in the kidney, aorta and heart at the end of treatment.Results: treatment with enalapril did not induce any changes in SBP, estradiol, androgen and FSH plasma levels.NOS activity (pmol/min 100g tissue), * p<0.01 vs ControlConclusions: The ACE inhibition did not modify SBP or sexual hormones in normotensive menopause rats, but treatment with enalapril improved NOS activity significantly in all the studied tissues. This fact could improve renal and cardiovascular function during menopause.
Electrophysiological properties of enkephalinergic neurons visualized in BAC transgenic mice
Authors: Tsuda Masayuki , Takasusuki Toshifumi , Hori Yuuichi 
Published: June 2021

Enkephalinergic neurons have been found in several areas of the central nervous system, including the spinal cord dorsal horn, where they play an important role in the transmission and modulation of nociceptive information. In an attempt to visualize enkephalinergic neurons in vivo, we generated a Bacterial Artificial Chromosome transgenic mouse in which enhanced green fluorescent protein (EGFP) is expressed in enkephalinergic neurons under the control of the preproenkephalin gene promoter. Immunohistochemical studies indicated that the expression pattern of EGFP is similar to that of endogenous enkephalin.Patch‐clamp recordings were made from EGFP‐fluorescent neurons located in the superficial dorsal horn of spinal cord slices, and the electrophysiological properties of these neurons were investigated. Some neurons exhibited bursts of action potentials throughout a depolarizing current pulse, other neurons showed a strong accommodation of action potentials, and other neurons fired a single action potential in response to a depolarizing current pulse. The remaining neurons showed different firing patterns. EGFP‐fluorescent enkephalinergic neurons in the superficial dorsal horn come in a variety of electrophysiological properties.This work was supported by grants from the Promotion and Mutual Aid Corporation for Private Schools of Japan (MT).
High salt intake deteriorates cardiac function of hypertrophied heart, possibly via excessive sympathetic drive
Authors: koji Ito , Hirooka Yoshitaka , Sunagawa Kenji 
Published: June 2021

Background: High salt intake often results in congestive heart failure in patients with left ventricular hypertrophy (LVH). We hypothesized that excessive sympathetic activation associated with salt intake plays a significant role in developing cardiac dysfunction.Methods and Results: We used ICR mice and applied aortic banding (AB) to create LVH. Four weeks after the banding, 24‐h urinary norepinephrine excretion (U‐NE) was higher in AB mice than in controls. LV function evaluated echocardiographically, however, was not different between groups. We then fed the mice a high salt diet (8%) for 4 weeks. LV function decreased in the AB mice compared with controls and was significantly worse in the high salt (HS)‐AB mice than in regular salt (RS)‐AB mice (LVDD: 3.5±1 vs 3.2±2 mm, wall thickness: 1.4±0.3 vs 1.2±0.1 mm, fractional shortening: 30±4 vs 44±1 %, all p<0.05). U‐NE was higher in HS‐AB than in RS‐AB mice. Further, the mice fed a high salt diet concurrent with AB developed LVH after 4 weeks, but LV systolic function remained normal without increases in U‐NE.Conclusions: In mice with LVH, high salt intake deteriorates cardiac function possibly through sympathetic overactivation. These results suggest that sympathetic activation plays a key role in the development of cardiac dysfunction.
Progressive Heat Storage during Intermittent Work
Authors: Kenny Glen Patrick , Dorman Lucy , Gagnon Daniel , DuCharme Michel , Webb Paul , Reardon Francis , Jay Ollie 
Published: June 2021

Ten participants (5M, 5F) completed 3 × 30‐min bouts of exercise (Ex 1, 2, 3) at a metabolic heat load (M‐W) of 505±7 W separated by 3 × 15‐min recovery (Rec 1, 2, 3) in an air calorimeter at 30°C, 30% RH. Rates of evaporative heat loss (EHL), dry heat loss (DHL) and M‐W were measured throughout by whole‐body direct calorimetry, giving changes in body heat content (ΔHb). Rectal (Tre), quadriceps (Tquad) and triceps (Ttri) temperature were measured throughout. ΔHb progressively increased from the end of Ex 1 (242±18 kJ) to end Ex 2 (308±29 kJ), to end Ex 3 (341±46 kJ). Heat content dissipated during Rec 1 (−63±10 kJ) was similar to Rec 2 (−74±9 kJ) and Rec 3 (−73±7 kJ). Tre progressively increased from 36.88±0.11°C at rest to 37.41±0.12°C at the end of Ex 1, 37.64±0.12°C (Ex 2), and 37.74±0.12°C (Ex 3). Ttri increased from 33.91±0.19°C at rest, to 34.86±0.25°C (Ex 1), 35.23±0.28°C (Ex 2), and 35.40±0.33°C (Ex 3). However, after an initial increase in Tquad from 34.62±0.14°C at rest to 36.82±0.16°C (Ex 1), no further significant elevations were observed. DHL was between ~50 and 65 W throughout. At the end of Ex 1 (383±25 W), Ex 2 (398±9 W) and Ex 3 (413±9 W) EHL was similar; however EHL increased at a greater rate during Ex 2 and 3 relative to Ex 1. Progressive elevations in body heat content, core temperature and inactive muscle temperature occurred with intermittent exercise.Supported by NSERC and US Army Medical Research Grant.
Exogenous ATP abolishes postjunctional α1‐ and α2‐adrenergic vasoconstriction in humans
Authors: Kirby Brett S , Carlson Rick E , Voyles Wyatt F , Dinenno Frank A 
Published: June 2021

Recent evidence suggests that adenosine triphosphate (ATP) can inhibit vasoconstrictor responses to endogenous norepinephrine release via tyramine, similar to what is observed in contracting muscle. Whether this involves a reduction in postjunctional α‐adrenergic receptor responsiveness is unclear. Therefore, we tested the hypothesis that exogenous ATP can blunt direct postjunctional α‐adrenergic vasoconstriction in humans. We measured forearm blood flow (FBF; Doppler ultrasound) and calculated the vascular conductance (FVC) responses to local intra‐arterial infusions of phenylephrine (α1‐agonist) and dexmedetomidine (α2‐agonist) during moderate rhythmic handgrip exercise, during a control non‐exercise vasodilator condition (adenosine), and during ATP infusion in 7 young adults. Forearm hyperemia was matched across all conditions. Forearm vasoconstrictor responses to direct α1‐receptor stimulation were blunted during exercise vs adenosine (ΔFVC = −11±3% vs −36±5%; P<0.05), and were abolished during ATP infusion (−4±3%). Similarly, vasoconstrictor responses to α2‐receptor stimulation were blunted during exercise vs adenosine (−12±4% vs−37±9%; P<0.05), and were abolished during ATP infusion (−3±5%). We conclude that exogenous ATP abolishes postjunctional α‐adrenergic vasoconstriction, and this involves both α1‐ and α2‐receptor subtypes.Supported by AG‐022337, HL‐087952
Local H1‐and H2‐receptor blockade blunts postexercise blood flow in the vastus lateralis
Authors: Pellinger Thomas K , Simmons Grant H , Halliwill John R 
Published: June 2021

Orally administered histamine H1‐ and H2‐receptor blockade blunts the sustained (90 min) hyperemia present in the previously exercised limbs of humans following dynamic exercise. Our aim was to determine if this postexercise hyperemic response could be prevented by local H1‐ and H2‐receptor blockade administered via skeletal muscle microdialysis. Thus, we tested the hypothesis that postexercise ethanol outflow/inflow ratios (an inverse surrogate of local blood flow) would be higher in sites that received H1‐ and H2‐receptor blockade versus control sites. Four microdialysis probes were inserted into the vastus lateralis muscle of five healthy subjects (21–26 yrs) immediately after 60 min of upright cycling at 60% VO2 peak. Microdialysis probes were perfused with a modified Ringer's solution containing 5 mM ethanol. Two of the sites received H1‐ and H2‐receptor antagonists (1 mM pyrilamine/3 mM cimetidine) and two sites served as controls. Consistent with our hypothesis, one hour after exercise, the outflow/inflow ratio was 0.48 ± 0.02 in blockade sites versus 0.41 ± 0.03 in control sites (P = 0.042). In addition, three subjects underwent a sham protocol (no exercise) in which blockade did not affect the ethanol outflow/inflow ratio (P ≥ 0.143). These results suggest that local H1‐ and H2‐receptors in skeletal muscle contribute to postexercise hyperemia.Supported by AHA grant 555623Z and the Evonuk Foundation
mTOR signaling following Essential Amino Acid + Carbohydrate Ingestion in Young and Older Subjects
Authors: Dreyer Hans Christian , Fujita Satoshi , Drummond Micah John , Rasmussen Blake , Volip Elena 
Published: June 2021

Essential amino acid (EAA) ingestion can stimulate muscle protein synthesis in young and older subjects. In older subjects however, the addition of carbohydrate (CHO) (EAA+CHO) has been shown to blunt the anabolic response as compared to young subjects and may be due to dysregulation of the anabolic (mTOR) signaling pathway.PURPOSE:The purpose of this study was to determine the signaling response after ingestion of EAA + CHO in young and older muscle and to determine if the response between groups was different.METHODS:Immunoblotting methods were used to determine cell signaling of an anabolic pathway (mTOR), at 1 and 2hr post EAA+CHO ingestion.RESULTS:Our preliminary results from 4 young and 5 older subjects demonstrate that Akt, mTOR, S6K1 and 4E‐BP1 phosphorylation increased following EAA+CHO ingestion while eEF2 phosphorylation decreased only in young. In addition there was a trend for 4E‐BP1 phosphorylation to be greater in the young at 1h post ingestion (P=0.09).CONCLUSIONS:Our preliminary findings suggest that a potential differential response to EAA+CHO ingestion exists between young and old. This response may indicate that both translation initiation (4E‐BP1 phosphorylation) and elongation (eEF2 dephosphorylation) may be attenuated in the old. Further research in needed to elucidate the potential differential response between young and old muscle following EAA+CHO ingestion.This work was supported by a Pepper Pilot Project award
Identification and characterization of a novel Muscle Lamin A/C (LMNA) Interacting Protein (MLIP): A regulator of Pax7
Authors: Ahmady Elmira , Burgon Patrick G 
Published: June 2021

Specific missense mutations LMNA have been identified to be associated with muscular dystrophy suggesting that LMNA interacts with a muscle specific factor(s). A yeast two‐hybrid screen with LMNA as bait was employed to identify muscle specific proteins. A previously uncharacterized cDNA clone was identified that interacts with LMNA in muscle, MLIP. Preliminary results show MLIP protein is primarily expressed in brain, heart and skeletal muscle. No structural or functional domains have been identified within MLIP.Objective: To define the function of MLIP in muscle.Results: MLIP is expressed endogenously in a mouse myoblast cell line (C2C12) and is co‐localized to the nuclear envelope and PML bodies. Initiation of C2C12 differentiation led to a 3‐fold increase in MLIP expression peaking at 24hrs and MLIP continued to be expressed in differentiated myotubes. Specific knockdown of MLIP in C2C12 cells by shRNAi led to significant (p<0.01) reduction in Pax7 expression with a concurrent reduction in Myf5, MyoD and myogenin with Pax3 expression being unaffected. To determine whether MLIP is necessary and/or sufficient for myogenic differentiation, stable C2C12 cell lines are being generated that either knockdown MLIP or over‐express MLIP.Conclusion: MLIP is a novel LMNA interacting protein that may regulate Pax7 a myogenic determinant during regenerative myogenesis. Funding: CIHR operating grant to PGB.
REDD2 inhibits mTOR signaling in skeletal muscle cells
Authors: Miyazaki Mitsunori , McCarthy John J , Zhang Xiping , Esser Karyn A 
Published: June 2021

The protein kinase mTOR (mammalian target of rapamycin) is established in skeletal muscle as a key signaling hub during cell growth/hypertrophy. In this study, we determined that the stress responsive gene REDD2 inhibits mTOR signaling in skeletal muscle cells. The effects of REDD2 expression on mTOR activity were also determined in C2C12 muscle cell. Overexpression of REDD2 resulted in decreased mTOR kinase activity under both basal and amino acid‐stimulated conditions. These inhibitory effects on mTOR signaling are mediated downstream of Akt but upstream of Rheb. Knock down of TSC2 (tuberous sclerosis complex 2) using siRNA potently activated mTOR signaling and was sufficient to rescue REDD2 inhibition of mTOR activity. Consistent with the in vitro studies, REDD2 mRNA levels are rapidly reduced in the plantaris muscle during hypertrophy and increased in vivo during atrophic conditions. These results indicate that REDD2 negatively regulates mTOR activity likely through modulation of TSC2 function and regulating of REDD2 might regulation of muscle cell size in mice.This study is supported by the grant provided from National Institute of Health (AR45617).
Prevention of Emphysema‐Induced Reductions in Diaphragm Muscle Mass
Authors: Mattson John Paul , Hinkle Richard T , Isfort Robert J , Ferreira Leonardo F , Musch Timothy I , Poole David C 
Published: June 2021

Chronic hypercapnic COPD patients have an unfavorable prognosis. Respiratory muscle atrophy and weakness may lead to CO2 retention and ultimately respiratory failure. Therefore, the purpose of this investigation was to determine whether PG‐873637, a corticotrophin‐releasing factor 2 receptor‐selective agonist, would ameliorate diaphragm atrophy and/or induce hypertrophy.To establish the time course of emphysema induced diaphragmatic atrophy, costal diaphragm mass was measured at 4 and 8 months following saline (control) or elastase (emphysema) instillation in hamsters. Subsequently, after demonstration of atrophy, control and emphysema hamsters were treated with either saline (vehicle) or PG‐873637 (treatment) for 1 or 5 months prior to sacrifice.Excised lung volume increased (>140%) with emphysema at all time points. PG‐873637 treatment increased diaphragm muscle mass at both time points in emphysema animals (1‐month = 13% and 5‐month = 12%). These data demonstrate that PG‐873637 is efficacious as a treatment to preserve mass or induce hypertrophy in the emphysematous diaphragm.
Intracellular Critical PO2 Measured in Human Skeletal Muscle In Vivo
Authors: Lanza Ian R , Befroy Douglas E , Tevald Michael A , Kent‐Braun Jane A 
Published: June 2021

Under some conditions, intracellular oxygen tension (PO2) may decrease to the point where oxygen availability limits respiration. Information about this critical PO2 and its determinants in vivo is sparse. PURPOSE: To determine the critical PO2 of human skeletal muscle, and its relationship to cellular energy consumption. METHODS: Interleaved proton and phosphorus magnetic resonance spectroscopy were used to quantify deoxymyoglobin and phosphorous metabolites in the tibialis anterior muscle of 6 subjects during 15 minutes of leg ischemia. Critical PO2 was determined as the PO2 at the phosphocreatine inflection point during ischemia. The rate of ATP consumption was determined from the linear slope of PCr depletion following the inflection point. RESULTS: The time to PCr inflection point was 282 ± 112 s (mean±SE). The corresponding critical PO2 was 0.47±0.27 torr, with a range of 0.21–0.96. PO2crit was not associated with the resting rate of ATP consumption (r =0.17), but was directly correlated to the rate of myoglobin desaturation (r =0.93) and inversely correlated to the time required to reach the PCr inflection point (r = −0.74). CONCLUSION: These data suggest that the relatively wide range of PO2crit in these subjects is attributable to inter‐subject differences in the ability of the muscle to maintain ATP production in the face of an ischemic insult.Support NIH AG21094, K02 AG023582
Orai1 expression and function in vascular smooth muscle cells
Authors: Li Jing , Jairaman Amit , Sukumar Piruthivi , Porter Karen , Beech David 
Published: June 2021

Recent studies suggest TRPC5 is a component of calcium‐entry channels that help drive vascular smooth muscle cell migration (Xu et al 2006, Circ Res 98, 1381–9). Here we investigated another type of channel protein (Orai1) which is distinct from the TRP proteins and has been suggested to have pivotal roles in calcium‐entry of lymphocytes (Hogan & Rao 2007, Trends Biochem Sci 32, 235–45). Our experiments focused on proliferating vascular smooth muscle cells of the human saphenous vein. Quantitative RT‐PCR revealed high levels of mRNA encoding Orai1 and its homologues Orai2 and Orai3. Calcium‐entry was measured in the cells after store‐depletion with thapsigargin and using fura‐2 indicator dye on a real‐time 96‐well plate reader. RNAi knock‐down of Orai1 suppressed calcium‐entry, while knock‐down of Orai2 or Orai3 had no effect. Functional relevance was studied using modified Boyden chamber assays to quantify cell migration (chemotaxis) and invasion (through basement membrane matrix) in the absence of store‐depletion. Knock‐down of Orai1 markedly suppressed migration and invasion. Invasion is facilitated by secretion of matrix metalloproteinases (eg MMP‐2) but knock‐down of Orai1 had no significant effect on secretion of MMP‐2. The data suggest Orai1 is a novel calcium channel protein of vascular smooth muscle cells with important roles in cell motility.Supported by the British Heart Foundation and Wellcome Trust.