bluuebunny/crossref_metadata_2025_split huggingface dataset:
Skeletal Muscle Regulatory Responses to Increased Extracellular Lactate
Authors: Lindinger Michael I , Leung Matt , Moradi Jasmin , Shortreed Karin E , Hawke Thomas J 
Published: June 2021

Mammalian skeletal muscle cells exhibit cell shrinkage followed by regulatory volume increase (RVI) in response to increases in extracellular osmolarity caused by addition of concentrated NaCl or sucrose. We hypothesized that increased extracellular sodium lactate would similarly result in a transient loss of cell volume, followed by RVI, and that the RVI would be more rapid and pronounced than that seen with NaCl due to entry of lactate into the cell. The present study measured the time course of change single fibre width in response to varied increases in extracellular NaCl or Na‐lactate. Adult mouse EDL single fibres were isolated using collagenase and incubated in DMEM prior to and during experimentation. Fibre images were obtained at 3–6 s intervals for up to 40 min. Fibre images were analyzed for width at 2 sites. Increased osmolarity resulted in a rapid decrease in fibre width, followed by RVI. The volume recovery was faster and more complete when [lactate] ≥20 mmol/L. There was a linear relationship between increases extracellular [lactate], cell shrinkage, and magnitude of RVI. It appears that the inward transport of lactate into skeletal muscle contributes, together with increased NKCC activity, to the RVI in mammalian skeletal muscle.Supported by NSERC of Canada.
Will stripping of the great saphenous vein for venous insufficiency also improve the rise in arterial leg blood flow during exercise?
Authors: Nadland Inger Helene , Wesche Jarlis , Sheriff Don , Toska Karin 
Published: June 2021

Competent venous valves and the leg muscle pump are important for adequate return of blood to the heart. However, the role of this muscle pump for the rise in arterial blood flow to active skeletal muscle is incompletely understood. We have shown that the leg muscle pump does indeed increase muscle perfusion during upright exercise in healthy subjects (Nådland et al. Eup J appl physiol 2009), and that this mechanism is absent in patients with isolated insufficiency of the great saphenous vein (GSV) (FASEB J 23: 777.3, 2009). In the present study we investigated the muscle pump effect on the rise in muscle perfusion in these patients after treatment for GSV insufficiency, i.e. after stripping of the GSV (N=8).Beat‐to‐beat femoral artery blood flow (Ultrasound Doppler) was recorded continuously during calf exercise in supine and 30 degree head up tilted (HUT) positions. Because arterial and venous pressures in the legs increase with the height of a hydrostatic column, any muscle pump effect is more pronounced in an upright position. Thus the rise in blood flow from rest to exercise in the supine and in the 30 degree HUT positions was compared.The rise in femoral flow within 15 seconds of the start of exercise was 0.20 and 0.28 L/min above rest in the supine and HUT positions, respectively.These results indicate GSV stripping can improve the leg muscle pump effect on the rise in arterial leg blood flow during muscle work in these patients.
Skeletal muscle protein synthesis is elevated after moderate‐intensity aerobic exercise
Authors: Reidy Paul , Konopka Adam , Trappe Todd , Harber Matthew 
Published: June 2021

The acute influence of aerobic exercise on muscle protein turnover is not well defined. The purpose of this study was to examine the influence of moderate intensity aerobic exercise on muscle protein synthesis in the fasted and fed states. Eight recreationally active males (23±2yr, 74±3kg, VO2max: 52±2 ml·kg−1·min−1) performed 60min of cycle ergometry at 72±1% VO2max on two occasions in a counter‐balanced design. Trials differed only in a post‐exercise nutritional intervention. Subjects ingested a non‐caloric placebo (FAST) beverage or a beverage containing (per kg body weight): 5kcal, 0.83g carbohydrate, 0.37g protein and 0.28g fat (FED) immediately and 1h after exercise. Mixed muscle protein synthesis (FSR) was assessed at rest and following exercise with the use of an L‐[ring D5]‐phenylalanine infusion combined with muscle biopsies at 2 and 6h post‐exercise. Mixed muscle FSR was higher (P<0.05) after exercise in both FAST (0.112 ± 0.010%·h−1) and FED (0.129 ± 0.014 %·h−1) trials as compared to rest (0.071 ± 0.005 %·h−1). These data demonstrate that a moderate intensity, non‐exhaustive bout of aerobic exercise stimulates skeletal muscle FSR in the fasted state. Additionally, post‐exercise feeding did not further enhance FSR after aerobic exercise.Supported by a grant from the Gatorade Sports Science Institute
Neuregulin‐1/erbB signaling in rostral ventrolateral medulla of brainstem is involved in blood pressure regulation alteration of major neurotransmitters
Authors: Matsukawa Ryuichi , Hirooka Yoshitaka , Nishihara Masaaki , Ito Koji , Kishi Takuya , Sunagawa Kenji 
Published: June 2021

BackgroundNeuregulin‐1 (NRG‐1) is a multifunctional modulator that acts through epidermal growth factor family of tyrosine kinase receptors, including erbB2‐4. In the central nervous system, NRG‐1/erbB pathway has been shown to affect both glutamatergic and GABAergic function. However, it is totally unknown if this signaling pathway is involved in central blood pressure regulation. Therefore, we determined if NRG‐1/erbB signaling in the rostral ventrolateral medulla (RVLM) contributes to blood pressure regulation by altering the major neurotranmsiiters' function.Methods and ResultsIn anesthetized male Wistar rats, we microinjected NRG‐1β(0.025 pmol), erbB2‐receptor antagonist (AG825: 1.0 pmol) into the RVLM. NRG‐1 decreased mean arterial pressure (MAP) and heart rate (HR) ΔMAP −23.2 ± 1.8 mmHg, Δ HR −40.7 ± 5.5 bpm, n=5), while AG825 increased MAP and HR (Δ MAP 19.2 ± 2.9 mmHg, ΔHR 16.8 ± 1.2 bpm, n=4). Pre‐microinjection of NMDA receptor antagonist (AP‐5) into the RVLM attenuated the AG825 induced‐pressor response (6.5 ± 1.2 mmHg). Pre‐microinjection of GABAA receptor antagonist (bicuculine) into the RVLM attenuated the NRG‐1β induced‐depressor response (−4.3 ± 2.5 mmHg).ConclusionNRG‐1/erbB signaling in the RVLM contributes to AP and HR regulation via the modulation of both glutamatergic and GABAergic function. This pathway in the RVLM is involved in neural control of blood pressure.
Photostimulation of Channelrhodopsin‐2 expressing ventral medullary astrocytes increases sympathetic nerve activity and blood pressure in rats
Authors: Marina Nephtali , Figueiredo Melina , Tang Feige , Kasparov Sergey , Gourine Alexander 
Published: June 2021

Astrocytes play an important role in the control of complex central nervous functions by regulating synaptic strength and information processing. Here we explored the potential role of ventral medullary astrocytes in the regulation of central sympathetic tone and blood pressure (BP). Adult rats received bilateral microinjections in the rostral ventrolateral medulla (RVLM) of AVV‐sGFAP‐ChR2(H134R)‐Katushka1.3, an adenovirus that expresses channelrhodopsin‐2 (ChR2) under the control of the astrocyte‐specific promoter GFAP. 7–14 days later, strong ChR2 expression was detected in ventral medullary astrocytes located in close proximity to tyrosine hydroxilase‐immunoreactive RVLM neurons. Unilateral stimulation with blue light (445 nm) increased BP (20.7 mmHg, n=11) and renal nerve sympathetic discharge (SND; 28.7 %, n=11). Application of the ATP receptor antagonist MRS 2179 (200 μM) on the ventral medullary surface decreased baseline SND (15%) and BP (7.5%). Photostimulation after ATP receptor blockade produced signtificantly smaller responses in SND (12.5%) and BP (5%).CONCLUSIONSActivation of ventral medullary astrocytes increases sympathetic activity and blood pressure at least in part via ATP‐dependent mechanisms. This is the first demonstration that astroglia may play an active role in shaping the patterns of central sympathetic outflow.
Apoptosis of astrocyte mediated by toll‐like receptor 4 and apoptosis signal‐regulating 1 (ASK1) in cardiovascular center causes excessive sympathoexcitation in hypertensive rats
Authors: Kishi Takuya , Hirooka Yoshitaka , Sunagawa Kenji 
Published: June 2021

BackgroundLong considered merely a mechanical support to neurons, astrocyte has been shown to protect and mediate neural function. We previously demonstrated that oxidative stress and apoptosis in the rostral ventrolateral medulla (RVLM) of brainstem increase sympathetic nerve activity (SNA). ASK1 plays a key role in the stress‐induced apoptosis. TLR4, known to regulate inflammatory reactions, activates ASK1. We hypothesized that apoptosis of astrocyte in the RVLM mediated by ASK1/TLR4 results in sympathoexcitation in hypertension.Methods and ResultsWe used 16–18 weeks old stroke‐prone spontaneously hypertensive rats (SHRSP) as a hypertensive model with increased SNA and Wister‐Kyoto rats (WKY) as control. Immunohistochemical staining revealed that the number of astrocyte in the RVLM was significantly lower in SHRSP than in WKY. The expression of TLR4 and ASK1 in the RVLM was significantly higher in SHRSP than in WKY (TLR4; 23±2%, ASK1; 44±5%, n=5 for each, p<0.01). Infusions of TLR4 antagonist (intracerebroventricularly, for 14 weeks) significantly reduced SNA only in SHRSP (−38±2%, n=5, p<0.01), not in WKY. The number of astrocyte and the expression of ASK1 in the RVLM were significantly higher in TLR4 antagonist‐treated SHRSP than in vehicle‐treated SHRSP.ConclusionApoptosis of astrocyte in the RVLM mediated by TLR4/ASK1 plays a key role for sympathoexcitation in hypertensive rats.
Altered regulation of sympathetic nerve activity by the caudal ventrolateral medulla and nucleus tractus solitarius in obese Zucker rats
Authors: Huber Domitila A. , Schreihofer Ann M. 
Published: June 2021

Obese Zucker rats (OZR) have higher sympathetic nerve activity (SNA) and arterial pressure (AP) compared to lean Zucker rats (LZR). The higher SNA in OZR is due to reduced GABAergic inhibition of rostral ventrolateral medulla (RVLM), the source of drive for SNA. Caudal ventrolateral medulla (CVLM) provides this inhibitory input to RVLM, and CVLM is driven by a glutamatergic input from nucleus tractus solitarius (NTS). We hypothesized the CVLM provides reduced tonic inhibition to RVLM in OZR due to a reduced glutamatergic drive from NTS. Adult male rats were anesthetized with urethane (1.5 g/kg, iv), ventilated, and paralyzed to record splanchnic SNA and AP. Compared to LZR (n=13), OZR (n=14) had higher SNA (2.7 ± 0.4 vs. 1.6 ± 0.2 μV, P<0.05) and mean AP (130 ± 2 vs. 123 ± 2 mmHg, P < 0.05). Inhibition of glutamatergic inputs to CVLM (kynurenate; 5.4 nmol/100 nl) evoked smaller rises in SNA in OZR (n=7) vs. LZR (n=7; 169 ± 23 vs. 289 ± 17 %, P < 0.05). This was not due to a reduced ability of GABA to inhibit RVLM because injections of GABA into RVLM (0.3, 1.0, 3.0 nmol) evoked comparable decreases in SNA in OZR (n=7) and LZR (n=7). Inhibition of NTS (muscimol; 100 pmol) evoked smaller rises in SNA in OZR (n=7) vs. LZR (n=6; 62 ± 11 vs. 112 ± 14 %, P < 0.05). These results suggest higher SNA in OZR may be due to reduced tonic GABA from CVLM. Further, reduced glutamatergic inputs from NTS to CVLM may contribute to diminished inhibition from CVLM to RVLM in OZR.Grant Support: NIH R01HL086759
Maternal Separation affects neurocircuitry of ether and restraint stress in adulthood
Authors: Foscolo Daniela Rocha Costa , Foscolo Rodrigo Bastos , Coimbra Candido Celso 
Published: June 2021

We investigated the effect of maternal separation on neural circuitry activation in response to stress in adulthood. Rats were submitted to maternal separation (180 min/day) during 2 first weeks of life. Two stress protocols were randomly performed at 10–12 weeks of age. 1) Restraint animals were placed into plastic tubes for 20 min or 2) exposed to ether for 10 min. After 90 min of the onset of stress situation rats were euthanized and brains were removed and processed for cFos immunohistochemistry in paraventricular (PVN), amygdaloid medial (AM), supraoptic nucleus (SO) and preoptic area (POA). Cathecolaminergic nucleus of brainstem tyrosine hydroxilase was also co‐localized. Maternal separation increased Fos activated neurons in both stress situations in most of nuclei evaluated, especially after ether stress. The number of neurons Fos positive was 180% higher on Locus Coeruleus (LC), 136% PVN and 170% APO after ether stress when compared to control group. On the other hand on restrain stress was 86% in LC, 125% in PVN, and 56% in APO higher. Maternal separation only affect activation in SO after restraint stress (73%). AM showed a similar response on both stress protocols (about 135% higher). Our data showed that maternal separation induces a heterogenic response on neural circuitry activation and interferes with the neuroendocrine programming early in life.Financial support CNPq, Fapemig
ATP mediates flow‐induced nitric oxide production in thick ascending limbs
Authors: Cabral Pablo Daniel , Garvin Jeffrey Lawrence 
Published: June 2021

Mechanical stimulation caused by increasing flow induces the release of ATP and other nucleotides. Both luminal flow and extracellular ATP stimulate production of nitric oxide (NO) in the thick ascending limb (TAL). We hypothesized that luminal flow‐induced NO production in TALs is mediated by ATP. We measured NO production in isolated, perfused rat TALs using the fluorescent dye DAF FM. The rate of increase in fluorescence reflects NO accumulation. Increasing luminal flow from 0 to 20 nL/min stimulated NO production from 17±15 to 130±34 arbitrary units (AU)/min (p < 0.04; n=7). When an ATP scavenging system (hexokinase; 10 U/ml plus 5.5 mM glucose) was added to the luminal perfusate and basolateral bath, luminal flow did not increase NO production (control: 32±5; after ATP scavenging: 19±4 AU/min; n=6). When luminal flow was increased with the ATPase apyrase (5 U/ml) in the luminal perfusate and basolateral bath, NO levels did not change significantly (control: 41±12; after apyrase: 59±11; n=6). The P2 receptor antagonist suramin (300 umol/L) in the lumen and bath reduced flow‐induced NO production by 73% (control: 56±11; with suramin: 13±12; n=5). We concluded that ATP mediates flow‐induced NO production in thick ascending limbs via P2 receptors.Support: PO1 HL 090550, RO1 HL 070985
Pregnant Diabetic Mice have Aberrant Blood Pressure Control and Renal Dysfunction Associated with Fetal Growth Restriction and Death
Authors: Burke Suzanne Diana , Barrette Valerie F , Adams Michael A , Croy B Anne 
Published: June 2021

Cardiovascular adaptations of pregnancy involve structural and functional changes in the heart and kidneys. Pregnant women with Type 1 Diabetes (T1D) are at high‐risk for developing pregnancy complications. Using radiotelemetry, we sought to investigate the blood pressure regulation of the pregnant T1D non‐obese diabetic (NOD) mouse.Diabetic NOD mice had a normal drop in blood pressure from gestation day 5–9, but became hypotensive and severely bradycardic during late gestation in comparison to pregnant, normoglycemic NOD mice. These acute hemodynamic changes were accompanied by biochemical and histopathological signs renal failure. Pups born to diabetic dams were growth‐restricted, suggesting placental insufficiency. The paradox of rapid onset renal dysfunction, combined with unexpected hypotension and bradycardia suggests that, in diabetes, pregnancy‐induced renal adaptations accelerate renal disease progression, compromising maternal and fetal circulatory health.Funded by CIHR, Canadian Foundation for Women's Health and the Canada Research Chairs ProgramGrant Funding Source: CIHR
Luteotropic Hormone (LH) effects on T‐type calcium currents and intracellular calcium transients are mediated by PKA in mice Leydig cells
Authors: Costa Roberta Ribeiro , Aguiar Jose Fernando , Varanda Wamberto Antonio 
Published: June 2021

Previous results from our laboratory have shown that LH is able to increase the intracellular Ca2+ concentration ([Ca2+]i) in Leydig cells, a process triggered by calcium entry through a T‐type Ca2+ channel. Here we describe the effects of modulators of PKC and PKA on the Ca2+ currents, measured with the patch clamp technique, and on the overall [Ca2+]i transients with fluorescence detection. Treatment of the cells with LH (1 μg/ml) increased the peak current at −20 mV from −2.4 ± 0.7 to −3.8 ± 0.8 pA/pF (n = 22, p = 0.0381). PMA (1 μM) increased the peak current to −3.6 ± 0.4 pA/pF (n = 6, p = 0.00033). Only minor changes were observed in the voltage dependence of activation, inactivation or deactivation of the currents. Experiments with the calcium sensitive dye Fluo‐3, showed that inhibition of both PKC and PKA with 400 nM staurosporine blocks the [Ca2+]i changes induced by LH (n = 37 cells). The specific inhibitor of PKA, H89 (10 μM) abolished the LH induced rise in [Ca2+]i (n = 48 cells). PMA slowly increases the fluorescence, but the subsequent addition of 1 μg/ml LH still triggers the typical [Ca2+]i transient showing that block of PKC alone does not inhibit the effect of LH. Chelerythrine, a PKC inhibitor, also does not avoid the Ca2+ transients. Taken together, our results support the conclusion that PKA plays a leading role in mediating the LH induced intracellular Ca2+ changes.Financial Support: FAPESP, CNPq
Hypertonic stress disrupts cellular protein homeostasis and causes rapid protein damage in vivo
Authors: Burkewitz Kristopher , Choe Keith P. , Strange Kevin 
Published: June 2021

It has long been assumed from in vitro studies that hypertonic stress (HS) disrupts protein structure and function. However, there is little in vivo evidence to support this hypothesis. We recently reported that protein degradation genes are essential for survival of C. elegans in hypertonic environments and that HS induces aggregation of the fluorescent protein Q35::YFP. We characterized the kinetics and cell biology of Q35::YFP aggregation by time‐lapse confocal microscopy. Q35::YFP aggregates accumulate in the cytosol and between myofilaments of muscle cells. Aggregates form within 1 h after HS, develop at a rate of 10 aggregates/worm/h, and double in volume every 15 to 30 min. Protein folding per se is also disrupted by HS in vivo. Temperature‐sensitive (ts) point mutations give rise to misfolded proteins and mutant phenotypes at high but not low or “permissive” temperatures. We characterized the phenotypes of worms harboring ts mutations in paramyosin and ras. Exposure to high temperature alone or HS at permissive temperatures caused identical mutant phenotypes indicating that cellular water loss disrupts in vivo protein folding. These and our previous findings demonstrate that HS causes rapid protein damage that must be ameliorated to ensure survival. Our results have important implications for understanding how cells respond to HS and how these response mechanisms may be impacted by disease and aging.This work was supported by NIH grant DK61168.
Leptin Signaling Through the PI3K‐PDE3B Pathway is Impaired During Chronic Hypoxic Exposure
Authors: Litvin David G , Tsipis Constantinos P , Puchowicz Michelle C , LaManna Joseph C 
Published: June 2021

BackgroundLeptin signaling in the brain plays a crucial role in energy homeostasis. Recent evidence suggests that in addition to JAK2‐STAT3, leptin activity is also mediated through an insulin‐like signaling pathway that relies on PI3K and PDE3B. Recent work indicates this pathway becomes deregulated during leptin resistance. We hypothesized that exposure to chronic hypoxia, a trigger of leptin release, may alter leptin signaling, thereby producing leptin resistance.ObjectiveTo investigate whether chronic hypoxic exposure alters central leptin signaling.Methodsmale C57BL/6 mice were exposed to either hypobaric hypoxia at a pressure of ~300 torr or normoxic conditions for 7 or 21 days. PDE3B and pSTAT3 positive cells were identified immunohistochemically. Central leptin levels were measured by western blot.ResultsRobust expression of pSTAT3 & PDE3B was observed at day 7 of chronic hypoxic exposure compared to normoxic controls. At 21 days exposure, pSTAT3 staining appeared indistinguishable from 7‐day samples. Conversely, PDE3B staining appeared markedly decreased when compared with 7‐day PDE3B positive samples, but still above normoxic controls.ConclusionsThese findings suggest chronic hypoxia may impair PI3K‐PDE3B signaling. PDE3B may mediate the mechanism leading to leptin resistance induced by sustained leptin release during chronic hypoxic exposure.Grant Funding Source: NIH Grant NS 38632
An Amphipathic Alpha‐Helical Domain Identified in Nucleoporins Plays a Role at The Nuclear Pore Complex of Saccharomyces Cerevisiae
Authors: Lazarus Michelle Denise , Natarajan Paramasivam , Wente Susan 
Published: June 2021

All macromolecular transport between the nucleus and cytoplasm occurs via nuclear pore complexes (NPCs) embedded in the nuclear envelope. NPCs are composed of multiple copies of proteins, termed nucleoporin (Nups) which assemble sequentially into nascent nuclear pores generated following fusion of the inner and outer nuclear membranes. While much is known about NPC structure, the mechanisms governing NPC biogenesis remain largely undefined. Recently, an amphipathic α‐helix (ALPS for ArfGAP1 lipid packing sensor) motif, which mediates protein association with highly curved liposomes, has been defined. This ALPS motif was identified in protein components of two early associating S. Cerevisiae (sc) NPC subcomplexes; the scNup84 subcomplex (specifically Nup85 and Nup120) and the scNup170 subcomplex (specifically Nup170 and Nup188) and may help proteins associate with newly developing NPCs. Utilizing microscopy techniques and yeast genetics we have identified an important role for the ALPS domain in vivo and our evidence suggests that ALPS domains of different NUPs have redundant functions. Utilizing in vitro liposome binding assays we find that the ALPS domain is sufficient for liposome binding and that this binding is dependent on liposome size. Together, this data provides the first evidence for an in vivo function of the ALPS motif with an impact in the broad membrane biology field, and concomitantly expands our understanding of NPC assembly.Grant Funding Source: IRACDA & RO1
The involvement of CD2AP and endocytic proteins during enteropathogenic E. coli (EPEC) pedestal formation
Authors: Guttman Julian Andrew , Lin Ann E. , Veiga Esteban , Cossart Pascale , Finlay B Brett 
Published: June 2021

Enteropathogenic Escherichia coli (EPEC) are extracellular pathogens that generate actin‐rich structures (pedestals) beneath the adherent bacteria as part of their virulence strategy. Pedestals are hallmarks of EPEC infections and their efficient formation in vitro routinely requires the phosphorylation of the EPEC effector protein Tir at Tyrosine 474 (Y474). This phosphorylation results in the recruitment and direct attachment of the host adaptor protein Nck to Tir at Y474 that is utilized for actin nucleation through a downstream N‐WASP/Arp2/3‐based mechanism. Recently, the endocytic protein clathrin was demonstrated to be involved in EPEC pedestal formation. Here we examine the organization of clathrin in pedestals and report that CD2AP, an endocytosis‐associated and cortactin binding protein, is a novel and important component for EPEC pedestal formation that also utilizes Y474 phosphorylation of EPEC Tir. We also demonstrate the successive recruitment of Nck then clathrin prior to actin polymerization at pedestals during the Nck‐dependent pathway of pedestal formation. This study further demonstrates that endocytic proteins are key components of EPEC pedestals and suggests a novel endocytosis subversion strategy employed by these extracellular bacteria.Grant Funding Source: CIHR, NSERC