bluuebunny/crossref_metadata_2025 huggingface dataset:
The Anoxic Reduction of Mitochondrial ROS Production Leads to Increased GABAergic Interneuron Activity and Electrical Suppression in Turtle Cerebral Cortex
Authors: Hawrysh Peter , Hogg David , Buck Les
Published: November 2023

The anoxia‐tolerant western painted turtle (Chrysemys picta bellii) has uniquely adapted to surviving extended periods of low O2 by reducing the activity of energy‐consuming pathways. The largest such pathway is the re‐establishment of neuronal ionic gradients following excitatory transmission. We hypothesize that the mitochondria serve as the initiator of neuronal silencing by sensing changes in O2 and triggering increased GABA release with the goal of reducing overall energetic demand. Here, we show that the reduction of mitochondrial O2 consumption during anoxia limits the production of reactive oxygen species (ROS), as evidenced by a fluorescence reduction of the ROS‐sensitive dye DCF during anoxia. Whole‐cell patch clamp recordings demonstrate that this reduction in ROS enhances both tonic and phasic post‐synaptic GABAA receptor currents. To determine how the reduction in ROS affects GABA release, we first determined the location of neurons that produce and release GABA. Fast‐spiking GABA‐releasing stellate interneurons were found to sparsely reside in the molecular and subcellular layers of the turtle cortex, based in immunohistochemical staining for glutamate decarboxylase and the voltage‐sensitive K+ channel subunit Kv3.1. These neurons fire action potential bursts at a frequency of 0.09 ± 0.01 Hz, which is the same frequency that GABAergic phasic currents occur in pyramidal neurons. Following the transition to anoxia or during pharmacological ROS scavenging with N‐acetylcysteine, stellate interneurons depolarize and become more excitable, as evidenced by the increased prevalence of action potentials between and during bursts. These results suggest that mitochondrial ROS signaling in stellate interneurons controls widespread GABAergic signaling in the turtle cortex.

Support or Funding Information

Research was supported by an Ontario Graduate Scholarship to Peter Hawrysh and a Discovery Accelerator Supplements NSERC grant to Les Buck.
Prolactin and Extracellular Osmolality Regulate Branchial clc2c Expression in Tilapia
Authors: Keith Paige L.K. , Hunt Bethany L. , Inokuchi Mayu , Yamaguchi Yoko , Seale Andre P. , Lerner Darren T. , Grau E. Gordon , Breves Jason P.
Published: November 2023

Varying and contending models have been proposed to explain how teleost ionocytes facilitate ion uptake from freshwater environments. A recently characterized member of the clc Cl− channel family (clc2c) has been proposed as a conduit for basolateral Cl− transport by Na+/Cl− cotransporter (ncc)‐expressing ionocytes of stenohaline zebrafish. It is unknown to what extent clc2c is expressed in gill of euryhaline species, such as Mozambique tilapia, and whether expression is modulated in response to extrinsic (salinity) and intrinsic (hormones) factors. Here, we investigated prolactin (Prl) and local osmotic control of clc2c mRNA levels. First, branchial clc2c expression was markedly enhanced in freshwater‐acclimated tilapia compared with seawater‐acclimated tilapia. To investigate endocrine control of this salinity‐dependent expression, we injected hypophysectomized tilapia with ovine Prl. Ovine Prl induced a >8000‐fold increase in clc2c expression from saline‐injected controls. To then test whether Prl regulates clc2c expression in a gill‐autonomous fashion, we incubated gill filaments for 24 hours in the presence of homologous Prls, Prl177 and Prl188. By 24 hours, Prl188 stimulated clc2c expression ~5‐fold from controls. We then incubated filaments in media ranging from 280 to 450 mOsm/kg for 3 hours to investigate the possibility that extracellular osmolality exerts a local effect on clc2c expression. clc2c showed higher expression with decreasing media osmolalities. Collectively, our results suggest that both hormonal and extracellular osmotic conditions direct clc2c expression in branchial ionocytes. We propose that multifactorial modulation of clc2c expression contributes to the excellent adaptability of Mozambique tilapia to variations in environmental salinity.

Support or Funding Information

Supported by Start‐Up Funds (Skidmore College) to J.P.B.
Acute Effect of Ischemic Preconditioning on V̇O2max and V̇O2 Kinetics at Supramaximal Intensity in High‐Level Runners: A Randomized Placebo‐ and Nocebo‐Controlled Study
Authors: de Castro Sabino‐Carvalho Jeann Lúccas , Lopes Thiago Ribeiro , Obeid‐Freitas Tiago , Ferreira Thiago Henrique Nunes , Succi Jose Ernesto , Silva Antonio Carlos , Silva Bruno Moreira
Published: November 2023

Background

Ischemic preconditioning (IPC; brief cycles of ischemia) has been reported to acutely improve aerobic capacity and performance in recreational athletes. However, placebo and nocebo effects have not been adequately controlled, strict criteria to confirm the maximal oxygen uptake (V̇O2max) have not been used and high‐level aerobic athletes have not been assessed. Therefore, we controlled placebo and nocebo effects to investigate if IPC improves aerobic capacity and performance in high‐level runners.

Methods

Fifteen men (age = 22 ± 3 years; V̇O2max = 67.7 ± 4.9 mL/kg/min; mean ± SD) and four women (age = 24 ± 4 years; V̇O2max = 55.8 ± 4.1 mL/kg/min) were assessed. All have been training in running teams (5 ± 2 years) and participating in official competitive events. Three interventions were used, in random order [IPC; placebo ultrasound (PL); and resting control (CT)]. A standardized explanation was provided, before interventions were applied, to inform that both IPC and PL would improve performance compared to CT and that IPC and PL would not cause any harm. After each intervention, a maximal incremental test (MIT) was conducted to measure the V̇O2max. Ten minutes later, a supramaximal (peak velocity + 0.5 km/h) constant test was done until voluntary exhaustion. This test was used to verify the V̇O2max, measure the time sustained at V̇O2max and assess aerobic performance [time to exhaustion (TLim)]. Verbal incentive was given by a blinded investigator. Interventions were compared by repeated measures ANOVA, followed by Bonferroni's post hoc, when necessary.

Results

V̇O2max (65.5 ± 6.6, 65.4 ± 7.2, and 64.8 ± 5.8 mL/kg/min for IPC, PL, and CT, respectively; P = 0.52), time at V̇O2max(49 ± 35, 54 ± 45, and 37 ± 24 s; P = 0.36), and V̇O2 kinetics (tau: 29 ± 4, 30 ± 4, and 28 ± 4 s; P = 0.84) were similar among interventions. TLim was longer in IPC (166 ± 13 s) and PL (165 ± 13 s) than CT (143 ± 13 s, P < 0.05). However, TLim was similar between IPC and PL (P > 0.05).

Conclusions

IPC improved aerobic performance compared to CT in high‐level runners, but the improvement was not superior to PL. Moreover, V̇O2max, evaluated by strict criteria, time at V̇O2max, and V̇O2 kinetics at supramaximal intensity were unchanged by IPC.

Support or Funding Information

J.L.C.S. and T.O. have been supported by scholarships from FAPESP (2014/15877‐8 and 2015/03572‐0, respectively). The project was funded by FAPESP (2014/25683‐6) and CNPq (461516/2014‐4).
Is There A Relationship Between Pulmonary Capillary Blood Volume And Intrapulmonary Arteriovenous Anastomosis Recruitment During Exercise?
Authors: Tedjasaputra Vincent , Collins Sophie É , Bryan Tracey L , van Diepen Sean , Bouwsema Melissa M , Stickland Michael K
Published: November 2023

Exercise results in the recruitment of anatomical intrapulmonary arteriovenous anastomoses (IPAVA). There is speculation that IPAVA recruitment may act as a ‘pop‐off’ valve once pulmonary capillaries are fully recruited during exercise to protect the lung from large increases in pulmonary arterial pressure. Recognizing that the pulmonary capillaries are fully recruited in the supine position, we hypothesized that IPAVA recruitment during incremental exercise would initially occur at a pulmonary capillary blood volume (Vc) that approximated the value observed in the supine position. Twenty healthy subjects (9 males, 11 females, means±SD, age: 27±7 yrs, VO2max: 49.9±10.5 mL·kg−1·min−1) performed cycling exercise at 30, 50, 70 and 90% of VO2max. Capillary blood volume (Vc) was determined using the multiple FIO2‐DLCO breath‐hold method in the supine and upright positions at rest, as well as during upright exercise. IPAVA recruitment was evaluated by agitated saline contrast echocardiography. Mean Vc was 80.2±17.2 mL in the resting upright position, which increased to 94.6±24.6 mL when supine (p=0.043). During incremental upright exercise, Vc increased up to 132.9±26.3 mL at peak exercise (p<0.01). IPAVA recruitment was detected in all subjects during exercise, and first occurred at a mean Vc of 93.8±16.0 mL, which is significantly greater than resting upright Vc (p<0.05), but similar to resting supine Vc (p=0.97). Results were similar in men compared to women, and results were consistent when adjusting for alveolar volume. IPAVA recruitment was observed at a capillary blood volume similar to the value observed in the supine position. As the supine position is widely believed to result in the perfusion of all pulmonary capillaries, these data support the hypothesis that recruitment of IPAVAs follows full recruitment of the pulmonary capillaries.

Support or Funding Information

Project funding provided by the Natural Sciences and Engineering Research Council (NSERC, PI M. Stickland), and the Canadian Respiratory Research Network (CRRN, PI M. Stickland). V. Tedjasaputra is supported by the The Lung Association of Alberta and NWT graduate studentship. M. Bouwsema was supported by NSERC and Alberta Innovates Health Solutions summer studentships.
Convective and Diffusive O2 Transport Mechanisms Mediate the Decrease in Peak Oxygen Uptake Following Long‐duration Spaceflight
Authors: Ade Carl J , Broxterman Ryan M , Moore Alan D , Barstow Thomas J
Published: November 2023

It is well established that maximal oxygen uptake (VO2max) is decreased following spaceflight and has historically been attributed primarily to ‘central cardiovascular’ limitations associated with decreases in plasma volume and cardiac output. Considering the adverse physiological adaptations to long‐duration microgravity that have been reported along the O2 transport pathway, we challenged this traditional hypothesis by determining the mechanistic role that changes in the two components of O2 transport [convective O2 delivery (QO2) and peripheral O2 diffusing capacity (DO2)] have on mediating the decrease in VO2max following long‐duration spaceflight. It was hypothesized that the significant decrease in VO2max, which spaceflight elicits, would be mediated by reductions in both QO2 and DO2. In 9 astronauts, hemoglobin concentration ([Hb]), peak power output (PPO), and VO2peak were measured before and after ~6 months aboard the International Space Station. Cardiac output (QT) was determined at workloads corresponding to 25% and 50% VO2max via a non‐invasive rebreathing technique. The QT:work rate relationship was determined for each participant for each test via linear regression and extrapolated to predict the QT at VO2max (QTmax). QO2, DO2 and the arterial‐venous O2 difference were calculated from these variables via integration of Fick's Principle of Mass Conservation and Fick's Law of Diffusion. VO2max significantly decreased from pre‐ to post flight (Preflight 3.08±0.75 l min−1 vs. Postflight 2.55±0.49 l min−1, P =0.008). The significant decrease in QTmax (−7.4±9.1%, P =0.05) and unchanged [Hb] resulted in a significantly decreased QO2 (−10.0±10.5%, P = 0.02). DO2 significantly decreased from pre‐ to post‐spaceflight (−27.5±24.5%, P =0.05), as did the peak arterial‐venous O2 difference (−9.2±7.5%, P =0.007). Using forward multiple linear regressions, a majority of the variance in VO2peak could be attributed to changes in QO2 and DO2 (R2 = 0.99, P <0.001). These data demonstrated that the decreased exercise capacity in astronauts following spaceflight was mediated by decreases in both convective and diffusive O2 transport. These findings support the hypothesis that an astronaut's postflight aerobic exercise capacity is determined by the integration of multiple factors along the O2 transport pathway.
Elevated inspired and end‐tidal PCO2 on the International Space Station
Authors: Hughson Richard L , Yee Nicholas , Greaves Danielle
Published: November 2023

The vision impairment intracranial pressure syndrome (VIIP) has recently been identified in astronauts living in space for long durations on the International Space Station (ISS). Although changes in hydrostatic pressure gradient resulting in chronic increases in cerebral artery and intracranial pressure are regarded as the most likely causes of VIIP, the elevated PCO2 in the atmosphere of the ISS is considered a potential contributor due to the vasodilatory effect of CO2 on cerebral and retinal arterioles. To date, there are no data published on the impact of elevated inspired PCO2 on arterial PCO2 during spaceflight. In the BP Reg study, we measured cardiac output by rebreathing providing an opportunity to obtain several breaths prior to rebreathing in which we could monitor inspired and expired PCO2. Here we report the averages from pre‐rebreathing PCO2 from inspiration and end‐tidal values (as indicators of the arterial PCO2) from 9 male astronauts during maneuvers in pre‐flight upright seated baseline testing and during spaceflight approximately 3 weeks before return to Earth. For each individual, all suitable breaths were averaged to a single value. Inspired PCO2 increased from pre‐flight baseline (0.6±0.12 mmHg) to inflight (3.8±0.44 mmHg, P<0.001). Expired, end‐tidal, PCO2 also increased from pre‐flight baseline (36.0±3.22 mmHg) to inflight (42.1±3.70 mmHg, P=0.004). The difference between end‐tidal PCO2 comparing inflight to pre‐flight (6.1±1.62 mmHg) was greater than the difference between inspired PCO2 comparing pre‐flight to inflight (3.3±0.46 mmHg, P<0.001). These data show that inspired PCO2 is elevated during spaceflight, but rather than an anticipated increase in alveolar ventilation to compensate for this increase in inspired PCO2, there might have been a reduction in alveolar ventilation resulting in an increase in end‐tidal PCO2 which is an indicator of arterial PCO2, although changes in ventilation‐perfusion should be considered. On Earth, a 6 mmHg increase in arterial PCO2 would be expected to increase brain blood flow over 15%; but, in spaceflight there appears to be no increase (Arbeille, 2001). Therefore, further studies are required to examine arterial PCO2 rather than end‐tidal, cerebrovascular reactivity to CO2 and cerebral blood flow to determine if elevated inspired PCO2 might contribute to the incidence of VIIP in astronauts.

Support or Funding Information

Supported by Canadian Space Agency
The Role of Prolonged Adenosine Triphosphate Infusion on Rapid Onset Vasodilation
Authors: Dillon Gabrielle , Shepherd John‐Roger , Dinenno Frank , Curry Timothy , Joyner Michael , Ranadive Sushant
Published: November 2023

Exercise‐induced rapid onset vasodilation produces a temporary rise in skeletal muscle blood flow in humans. The underlying mechanisms for this rapid hyperemia and regulation of muscle blood flow with single contraction are still not well understood. We tested the hypothesis that during a prolonged high dose intrarterial infusion of adenosine triphosphate (ATP; 20 μgrams ·100 mL forearm vol−1·min−1), the rapid onset vasodilatory response post‐single exercise contraction would be reduced compared to that of adenosine (ADO; 23 μgrams ·100 mL forearm vol−1·min−1). 14 healthy young participants (30 ± 1 years) performed a forearm single contraction exercise (20% of maximum) at minute 75 of either ATP (N=8) or ADO (N=6) continuous infusion. Artery diameter and blood velocity were measured using Doppler ultrasound. Forearm vascular conductance (FVC; ml·min−1·100 mmHg−1), time to peak, and area under curve were calculated. The mean resting FVC was higher during ATP (307.15 ± 50.56) and ADO (353.23 ± 43.98) infusion compared to saline infusion (45.17 ± 5.61 and 47.14 ± 5.57) (p<0.05). Compared to ADO, ATP infusion had a lower delta FVC from post‐ to pre‐contraction (174.06 ± 30.75 vs. 276.53 ± 24.90, p<0.05). Area under the curve and time of peak FVC did not significantly differ between drugs. These results suggest a prolonged ATP infusion may have blunted the rapid vasodilatory response more‐so than ADO. Thus, our findings indicate that ATP may be necessary but not obligatory in the rapid onset vasodilation response post‐single muscle contraction in humans.

Support or Funding Information

Supported by National Institutes of Health Research Grants HL‐119337 (to M.J. Joyner and F.A. Dinenno) and by CTSA UL1 TR000135. The Caywood Professorship (M.J. Joyner) via the Mayo Foundation also supported this research.
Cutaneous Blood Flow during Intradermal Exogenous Nitric Oxide Administration in Young and Older Adults: Roles for Cyclooxygenase and Calcium‐Activated Potassium Channels?
Authors: Fujii Naoto , Singh Maya Sarah , Minson Christopher T , Brunt Vienna E , Boulay Pierre , Sigal Ronald J , Kenny Glen P
Published: November 2023

Nitric oxide (NO) increases cutaneous blood flow. We hypothesized that cutaneous blood flow during intradermal administration of sodium nitroprusside (SNP, a NO donor) is in part regulated by cyclooxygenase (COX) and calcium‐activated potassium (KCa) channels in young adults. We also hypothesized that these contributions are diminished in older adults as ageing can reduce COX‐derived vasodilator prostanoids and downregulate KCa channels. In 10 young (3 males and 7 females, 23 ± 5 years) and 10 older (3 males and 7 females, 54 ± 4 years) adults, cutaneous vascular conductance (CVC) was measured at four intradermal forearm skin sites receiving 1) Ringers (Control), 2) 50 mM tetraethylammonium (TEA), a non‐specific KCa channel blocker, 3) 10 mM ketorolac, a non‐specific COX inhibitor, or 4) 50 mM TEA + 10 mM ketorolac. All skin sites were co‐infused with incremental doses of SNP (0.005, 0.05, 0.5, 5, 50 mM each for 25 min). Compared to the Control site, CVC during SNP administration was similar at the ketorolac site (0.005–50mM, all P > 0.05) but was lower at the TEA and TEA + ketorolac sites (0.005–5mM, all P < 0.05) in young adults. In older adults, ketorolac increased CVC relative to the Control site during SNP administration (0.005–0.5mM, all P < 0.05), but this increase disappeared when TEA was co‐administered (all P > 0.05). TEA alone did not modulate CVC during SNP administration in older adults (0.005–50mM, all P > 0.05). We show that during intradermal exogenous NO administration, KCa channels, but not COX, contribute to cutaneous blood flow regulation in young adults, while COX reduces cutaneous blood flow by attenuating KCa channel‐dependent cutaneous vasodilation in older adults.

Support or Funding Information

This study was supported by the Natural Sciences and Engineering Research Council of Canada (Discover grant, RGPIN‐06313‐2014; Discovery Grants Program ‐ Accelerator Supplement, RGPAS‐462252‐2014), and by Canada Foundation for Innovation (Leaders Opportunity Fund, 22529) (funds held by Dr. Glen P. Kenny).
Orthotopic versus Ectopic Tumor Perfusion During Exercise: Implications for Host Tissue Vasoreactivity
Authors: Garcia Emmanuel , Becker Veronika , Gittemeier Elizabeth Marie , Opoku‐Acheampong Alexander Boadu , McCullough Danielle , Behnke Bradley Jon
Published: November 2023

The microenvironment of solid tumors, like those present in prostate cancer, demonstrate heterogeneous blood flow patterns and regions of hypoxia that can impact the efficacy of radiation therapy. Studies designed to evaluate tumor hypoxia have utilized both ectopic (e.g. tumor cells implanted subcutaneously) and orthotopic (i.e. tissue of origin) tumor models. In orthotopic models, exercise has been demonstrated to reduce tumor hypoxia, whereas in ectopic models the effects of exercise are equivocal. Preliminary studies from our laboratory found a significant increase in blood flow to orthotopic prostate tumors (increase of 209 ± 22% vs. resting) versus a reduction in blood flow in ectopic tumors (decrease of 25 ±5 % vs. resting) during moderate intensity exercise (50–60% of maximal aerobic capacity)). Given this data, it was hypothesized that subcutaneous adipose arterioles and skin arterioles (ectopic host tissue) would have greater vasoconstriction versus prostate arterioles (orthotopic host tissue) in response to the alpha‐adrenergic agonist norepinephrine (NE). Six‐month old male Copenhagen rats (n=20) were used in this study. Resistance arterioles (<150 μm diameter) from the ventral lobe of the prostate, the rear flank skin, and the immediate subcutaneous adipose tissue were isolated and cannulated for in vitro analysis of vasomotor function. The latter two tissues form the bulk of the tissue representing the site of typical ectopic tumor models. The vessels were allowed to develop spontaneous tone. Thereafter, vasoconstriction to cumulative doses of NE (10−9 – 10−4 M) were recorded. There was a significantly higher peak vasoconstriction to NE in subcutaneous adipose arterioles (92 ± 7%; P<0.05) versus both skin (59 ± 8%) and prostate (55 ± 7%) arterioles. There were no significant differences in vasoconstriction between skin and prostate arterioles. In conclusion, during exercise when sympathetic nerve activity is increasing, the greater vasoconstriction in the host‐tissue arterioles of ectopic versus orthotopic tumor models likely contribute to the diametrically opposing rest‐to‐exercise tumor blood flow responses. Therefore, these data are critical to consider when selecting appropriate tumor models for exercise study designs.

Support or Funding Information

American Cancer Society (RSG‐14‐150‐01‐CCE), American Physiological Society and the National Institutes of Health (NHLBI; 1 R25 HL115473‐01).
Extracellular matrix affects endothelial cell attachment under shear flow
Authors: Chiu Yi‐Fan , Huang Bin
Published: November 2023

Shear flow plays an important role in cardioprotection. In the present In vitro study, shear flow is processed on a glass slide that coated with biomatrix so that the endothelial cells (ECs) can grow on it and then exposed to the shear flow. However, the detachment of ECs always hinders scientists to study the molecular aspect of cardioprotective mechanism. In the present study, the glass slides were washed either by hydrochloride (acidic wash) or sodium hydroxide (basic wash). After sterilized by ethanol, the glass slides were coated with three matrixes, poly‐L‐Lysine, fibronectin and collagen separately. Exposed the ECs to the shear flow of 5 dynes/cm2 and 20 dynes/cm2 for 2 hours, we investigated the attached cell number and their viability. The results showed that basic wash coupled with the coating of fibronectin has the best binding efficiency as compared to the others. The sustained expression of focal adhesion kinase (FAK) also supports our observation. As a result, our study provides a considerable application for the research of shear flow.

Support or Funding Information

MOST 104‐2632‐M‐037‐001, KMU‐TP104E13, KMU‐O104003, KMU‐O105001
Regular exercise reduces endothelial and whole artery stiffness in Western diet‐fed female mice
Authors: Padilla Jaume , Ramirez‐Perez Francisco I , Bostick Brian , Aroor Annayya R , Manrique Camila , Martinez‐Lemus Luis A , Sowers James R
Published: November 2023

We recently showed that Western diet (WD)‐induced obesity and insulin resistance promotes endothelial stiffness, which represents a distinguishing feature of endothelial dysfunction and is an instigator of vascular disease. Herein, we tested the hypothesis that an improvement in insulin sensitivity with regular exercise reduces the development of endothelial and whole artery stiffness in WD‐fed mice. Four‐week old female C57BL/6 mice (n=14) were randomized into sedentary or regular exercise conditions for 16 weeks. All mice were singly housed and fed a WD containing high fat (46%), high sucrose (17.5%), and high fructose corn syrup (17.5%). Exercising mice had access to voluntary running wheels throughout the study period and averaged ~7 km/day of running distance. Exercise training improved glucose tolerance and HOMA‐IR (p<0.05) in the absence of changes in body weight and blood pressure. Compared to sedentary mice, exercise trained mice exhibited reduced ex vivo aortic endothelial stiffness (sedentary: 11.9±1.7 kPa vs. exercise: 5.5±1.0 kPa; p<0.05), as assessed by atomic force microscopy, and reduced femoral artery stiffness in isolated pressurized arteries (p<0.05). In addition, exercise training led to an increase in femoral artery diameter and wall cross‐sectional area (p<0.05) indicative of outward hypertrophic remodeling. Collectively, these data indicate for the first time that regular exercise reduces endothelial and whole artery stiffness in insulin resistant female mice fed a WD. These favorable exercise‐induced vascular adaptations were associated with improvements in glucose tolerance and independent of changes in body weight and blood pressure.
Microvascular Responsiveness to Exogenous H2S is similar between Normotensive and Hypertensive Adults
Authors: Kutz Jessica L , Greaney Jody L , Santhanam Laskshmi , Alexander Lacy M
Published: November 2023

Hydrogen sulfide (H2S) is an endothelium‐derived hyperpolarizing factor (EDHF) that elicits cutaneous vasodilation in healthy young adults. H2S also functionally interacts with both nitric oxide (NO) and cyclooxygenase (COX) signaling pathways. Despite noted vascular dysfunction in hypertensive animal models, vascular responsiveness to exogenous H2S is preserved. The aim of this study was to (1) examine cutaneous vascular responsiveness to exogenous H2S in normotensive (NTN) and hypertensive (HTN) adults and (2) to assess the functional interaction of H2S with the NO and COX vasodilatory signaling pathways. We hypothesized that vascular responsiveness to exogenous H2S would be preserved but that functional interactions with both NO and COX would be diminished in HTN adults. Skin blood flow (laser Doppler flowmetry) responses were measured during graded intradermal microdialysis infusion of the H2S donor Na2S alone (CONTROL; 0.01mM – 100mM) and during co‐infusion with the non‐specific NO synthase inhibitor L‐NG‐Nitroarginine Methyl Ester (L‐NAME; 20 mM), the non‐selective COX inhibitor ketorolac (KETO; 10 mM), and combined L‐NAME+KETO in the ventral forearm of 7 NTN [age: 56±1 yrs; resting blood pressure (BP) 110±4/73±2 mmHg) and 7 HTN (age: 60±3 yrs; resting BP 144±5/86±3 mmHg) adults. Sigmoidal dose‐response curves were generated and the logEC50 was used as an index of vascular responsiveness. Cutaneous vascular responsiveness to Na2S was not different between groups (1.37±0.12 NTN v. 1.57±0.13 HTN; P>0.05). In NTN adults, there was a rightward shift in the dose‐response curve during L‐NAME (1.83 ± 0.07), KETO (2.07 ± 0.18), and COMBO infusion (2.33 ± 0.13; P<0.05 for all). In contrast, in HTN adults, separate infusion of L‐NAME (1.64 ± 0.06) or KETO (2.05 ± 0.20) had no effect (P>0.05 for both) on Na2S‐induced vasodilation; however, combined inhibition elicited a rightward shift in the dose‐response curve (2.25 ± 0.20; P<0.01). These data suggest that vascular end‐organ responsiveness to exogenous H2S is preserved in HTN adults, despite noted reductions in the contribution of the NO and COX signaling pathways to Na2S‐induced vasodilation.

Support or Funding Information

NIH HL093238‐06
Amplification of Endothelium‐Dependent Vasodilatory Signaling in Contracting Skeletal Muscle of Humans: Role of Inwardly Rectifying Potassium Channels
Authors: Hearon Christopher M , Luckasen Gary J , Larson Dennis G , Dinenno Frank A
Published: November 2023

The local vasodilatory response to muscle contraction is due in part to the activation of inwardly rectifying potassium (KIR) channels and subsequent smooth muscle cell hyperpolarization. In addition to direct activation of KIR channels via elevated extracellular potassium, KIR channels may function as “amplifiers” of electrical signals originating from the endothelium and thus augment vasodilatory responsiveness to endothelium‐derived hyperpolarizing signals. In this study, we tested the hypothesis that exercise will selectively amplify vasomotor responses to the endothelium‐dependent vasodilator acetylcholine (ACh) and that this effect will be mediated in part by activation of KIR channels.

Methods

In a total of 15 young adults, we measured forearm blood flow (Doppler ultrasound) and calculated changes in vascular conductance (FVC) to local intra‐arterial infusion of ACh or sodium nitroprusside (SNP) during: 1) control resting conditions, 2) mild handgrip exercise (5% maximum voluntary contraction [MVC]), or 3) pharmacologically induced vasodilation (either by ACh or SNP infusion) to match the level of hyperemia observed during mild exercise, thus serving as a “high flow” resting condition. In the case of ACh, similar trials were performed before and after blockade of KIR channels via infusion of barium chloride, or pharmacological activation of KIR channels via infusion of potassium chloride (KCl).

Results

Mild handgrip exercise significantly augmented the peak vasodilatory response to the endothelium‐dependent vasodilator ACh (Δ FVC: control: 116 ± 13; exercise: 253 ± 19 ml/min/100mmHg; P<0.01; +124 ± 12%) but not the endothelium‐independent vasodilator SNP (Δ FVC: control: 144 ± 33; exercise: 116 ± 21ml/min/100mmHg; P=NS). There was no effect of high flow per se on peak vasodilatory response to ACh or SNP (Δ FVC: ACh: 143 ± 18; SNP: 125 ± 37 ml/min/100mmHg; both P=NS vs. respective control). Blockade of KIR channels attenuated the exercise‐induced augmentation of ACh‐mediated dilation (Δ FVC: control: 189 ± 24; exercise: 198 ± 19 ml/min/100mmHg; +9 ± 12%). In a follow up study, direct pharmacological activation of KIR channels via infusion of KCl amplified peak ACh‐mediated vasodilation relative to control ACh infusion (Δ FVC: control: 97 ± 15 vs. 142 ± 16 ml/min/100mmHg; respectively; +50± 9%). These findings provide evidence that muscle contractions amplify endothelium‐dependent vasodilatory signaling via activation of KIR channels in humans. Further, these studies support the idea that KIR channels may act as “amplifiers” of endothelium‐dependent hyperpolarization and that this may be an important mechanism contributing to the normal vasodilatory response to exercise.

Support or Funding Information

HL119337, HL095573
Endothelial Dysfunction following Prolonged Sitting is Mediated by a Reduction in Shear Stress
Authors: Restaino Robert M. , Walsh Lauren K. , Morishima Takuma , Vranish Jennifer R. , Martinez‐Lemus Luis A. , Fadel Paul J. , Padilla Jaume
Published: November 2023

We and others recently reported that prolonged sitting impairs endothelial function in the leg vasculature; however, the mechanisms remain unknown. Herein, we tested the hypothesis that a sustained reduction in flow induced shear stress is the underlying mechanism by which sitting induces leg endothelial dysfunction. Specifically, we examined whether preventing the reduction in shear stress during sitting would abolish the detrimental effects of sitting on popliteal artery endothelial function. In 9 young healthy men, bilateral measurements of popliteal artery flow‐mediated dilation (FMD) were performed before and after a 3‐hour sitting period during which one foot was submerged in 42°C water (i.e. WETFOOT), while the contralateral leg remained dry and served as internal control (i.e., DRYFOOT). Local heating is an effective stimulus for dilating the skin circulation and increasing limb vascular conductance and thus, shear stress without producing systemic cardiovascular effects. During sitting, popliteal artery mean shear rate was significantly (P<0.05) reduced in the leg of the DRYFOOT (pre sit: 44.1±4.9s−1, post sit: 25.4±3.8s−1) and sustained in the leg of the WETFOOT (pre sit: 39.6±3.7s−1, post sit: 40.7±5.5s−1). Popliteal artery FMD was impaired after 3 hours of sitting in the leg of the DRYFOOT (pre sit: 5.9±0.9% vs. post sit: 2.9±1.0%) but not WETFOOT (pre sit: 7.3±1.7% vs. post sit: 10.6±2.0%). Collectively, these data demonstrate that preventing the reduction of flow induced shear stress during sitting with local heating abolishes the impairment in popliteal artery endothelial function. Thus, a reduction in shear stress mediates sitting‐induced leg endothelial dysfunction.

Support or Funding Information

Support: NIH K01 HL‐125503 and R21 DK‐105368 (JP)
Vascular Responses to Hypovolemic Pressure Challenge in Individuals with Down Syndrome
Authors: Wee Sang Ouk , Rosenberg Alexander J. , Kanokwan Bunsawat , Griffith Garett , Baynard Tracy , Fernhall Bo
Published: November 2023

Aging is associated with altered vascular and autonomic function. Individuals with Down Syndrome (DS), experience premature aging, and exhibit autonomic dysfunction. Moreover, limited evidence suggests a link between autonomic dysfunction, arterial stiffness and vascular responsiveness to sympathoexcitation in individuals with DS, but this still remains unclear.

Purpose

To examine the differences in vascular responsiveness, specifically changes in arterial elastic properties, during sympathoexcitation using lower body negative pressure (LBNP) in individuals with and without DS.

Methods

Twenty four volunteers (DS=12, 24 yrs; Control=12, 23 yrs) participated in this study. Changes in vascular indices (β‐stiffness and elastic modulus (Ep) by carotid ultrasonography) were measured before, during and after LBNP (−20 mmHg).

Results

Individuals with DS showed lower VO2peak (25.0 ± 1.7 vs. 42.5 ± 1.7 ml/kg/min for DS and controls, respectively) and higher BMI (23.1± 1.7 vs. 31.9 ± 1.8 kg/m2 for controls and DS, respectively) (p<0.05). However, there was no group differences and no changes with LBNP in vascular or hemodynamics indices.

Conclusions

Our results demonstrated a lack of vascular responsiveness to sympathoexcitation in both individuals with and without DS. These findings may have been influenced by a lack of statistical power.

Hemodynamics and Arterial Stiffness

DS (N = 12)
Control (N = 12)

Baseline
LBNP (‐20mm Hg)
Recovery
Baseline
LBNP (‐20mm Hg)
Recovery

Carotid SBP (mmHg)
132 ± 6
129 ± 5
131 ± 5
125 ± 6
119 ± 5
124 ± 4

Carotid DBP (mmHg)
73 ± 3
74 ± 3
71 ± 3
75±3
74 ± 2
76 ± 3

Carotid MAP (mmHg)
94 ± 4
94 ± 3
93 ± 3
96 ± 3
93 ± 3
97 ± 3

β‐stiffness
5.44 ± 0.59
5.48 ± 0.37
5.78 ± 0.60
6.02 ± 0.56
6.59 ± 0.35
5.99 ± 0.57

Ep
71.22 ± 7.65
71.72 ± 4.57
72.94 ± 6.88
78.70 ± 7.26
82.80 ± 4.34
77.75 ± 6.52

Mean ± SEM, Significance level, p <0.05
Exercise Training Induced Regulation of Muscle Mitochondrial Dynamics
Authors: Fix Dennis K. , Hardee Justin P. , Gao Song , Hetzler Kimbell L. , Carson James A.
Published: November 2023

Introduction

Exercise training is a potent stimulator of muscle oxidative metabolism, which is tightly coupled to mitochondrial biogenesis, dynamics, and mitophagy. Mitochondrial dynamics involves the coordinated processes of fission and fusion. The IL‐6 family of cytokines can activate intracellular signaling pathways, such as STAT3, through the binding of their receptor complexes involving glycoprotein 130 (gp130). While systemic IL‐6 signaling can alter the expression of proteins related to mitochondrial dynamics, gp130 regulation of mitochondrial dynamic protein expression by exercise requires further investigation. The purpose of this study is to examine exercise training induced regulation of skeletal muscle mitochondrial dynamics.

Methods

Male, C57BL/6 (B6; N=18) and skeletal muscle‐specific gp130 knockout (skm‐gp130 KO; N=12) mice were assigned to either cage control (CC) or treadmill exercise training (EX) beginning at 6 weeks of age. EX mice performed 6 weeks of treadmill exercise (5% incline, 18 m/min, 55 min/d, 6 d/wk) and were sacrificed 48 hours after the last training session. Gastrocnemius protein expression of mitochondrial dynamics and mitophagy by Western blot.

Results

Exercise‐induced improvements in oxidative capacity were accompanied by increased muscle gp130 protein expression regardless of genotype. In B6 mice, EX training increased Fis1 protein expression and decreased Mfn‐1 protein expression. Interestingly, skm‐gp130 KO increased Fis‐1 protein expression and decreased Mfn‐1 protein expression. There were no further effects of EX on Fis1 or Mfn‐1 protein expression in skm‐gp130 KO mice. EX and and skm‐gp130 KO increased Beclin‐1 protein expression, and was further increased by exercise in skm‐gp130 KO.

Conclusions

Our results demonstrate that skeletal muscle gp130 knockout did not block the induction of muscle oxidative capacity by treadmill exercise training. We found that the deletion of skeletal muscle gp130 altered protein expression related to mitochondrial fission, fusion, and mitophagy. These findings indicate that the gp130 receptor may be involved in the regulation of mitochondrial dynamics. Future studies are required to establish a mechanistic role of gp130 in the regulation of mitochondrial dynamics.
Evidence for a novel role for eNOS in the regulation of hepatocellular mitophagy
Authors: Sheldon Ryan , Morris E. Matthew , Linden Melissa A. , Meers Grace M. , Thyfault John P. , Laughlin M. Harold , Rector R. Scott
Published: November 2023

INTRODUCTION

Consistent with the well characterized role for endothelial nitric oxide synthase (eNOS) to stimulate mitochondrial biogenesis, we have previously demonstrated that eNOS knockout (eNOS−/−) mice have reduced hepatic expression of PGC1α and TFAM in association with reduced mitochondrial respiratory capacity in western diet‐induced nonalcoholic steatohepatitis (NASH). Interestingly, hepatic mitochondrial content was preserved in eNOS−/−relative to wild‐type (WT) mice. This led us to hypothesize that eNOS concurrently regulates mitophagy (mitochondrial autophagy).

METHODS

WT and eNOS−/−mice were fed either a control or western‐style diet (WD; 45% fat, 1% cholesterol, 17% sucrose) for 18‐weeks. Whole liver homogenate and isolated hepatic mitochondria were assessed for markers of autophagy (cleaved microtubule‐associated protein 1A/1B‐light chain 3 [LC3‐II]) and mitophagy (BCL2/Adenovirus E1B 19kDa Interacting Protein 3 [Bnip3]). In a separate cohort of chow‐fed mice, primary hepatocytes from WT and eNOS−/− were isolated and cultured for 5‐days in a collagen matrix. Mitophagic flux was assessed via LC3‐II and Bnip3 accumulation following treatment for 16‐hours with 10 μM chloroquine (CQ; an inhibitor of lysosomal acidification) and 1 μM carbonyl cyanide 3‐chlorophenylhydrazone (CCCP) to induce mitochondrial depolarization in the presence or absence of 500 μM free fatty acids (FFA; 250 μM oleate + 250 μM palmitate).

RESULTS

WD increased the mitochondrial localization of LC3‐II and Bnip3 in both genotypes (p < 0.05, diet main effect), suggesting that WD increased hepatic mitophagic activity. However, eNOS−/−mice had reduced LC3‐II in liver homogenate (−45%) and isolated mitochondria (−28%) and lower Bnip3 (−25%) content in liver homogenate (genotype main effect; p < 0.05). eNOS−/−primary hepatocytes exhibited a blunted accumulation of LC3‐II (−31%) and Bnip3 (−22%) following 16‐hours of CQ+CCCP treatment compared to WT cells, and failed to further respond to FFA exposure (+32% in Bnip3 in WT vs. eNOS−/− hepatocytes).

CONCLUSIONS

Collectively these data identify a hepatocellular autonomous function of eNOS in the regulation of mitophagy in response to metabolic insult. This suggests that dysregulation of hepatocellular eNOS may contribute to the accumulation of damaged mitochondria and to the etiology of NASH.

Support or Funding Information

Support: MU Life Sciences Pre‐doctoral Fellowship (RDS), AHA 14POST20110034 (EMM), NIH R01DK088940 (JPT), NIH HL‐36088 (MHL), VHA‐CDA2 IK2BX001299 (RSR).
RESISTIN ENHANCES THE CENTRAL EFFECTS OF LEPTIN ON RENAL SYMPATHETIC NERVE ACTIVITY
Authors: Habeeballah Hamza , Alsuhaymi Naif , Stebbing Martin , Jenkins Trisha , Badoer Emilio
Published: November 2023

Background

Leptin is a well known hormone released from fat tissue and acts centrally to influence metabolic and cardiovascular functions. It increases renal sympathetic nerve activity (RSNA) and could be an important contributor to the abnormally elevated RSNA observed in obesity or overweight conditions. Resistin is also a hormone released from fat tissue and acts centrally to elicit effects on RSNA similar to those of leptin. The question arises as to whether resistin can enhance leptin's actions on RSNA. Although the brain nuclei activated by leptin are well known, there has not been a systematic investigation of those activated by resistin. We investigated the effects of acute central administration of leptin and resistin on RSNA. We also used Fos protein to quantify the number of activated neurons in the brain following each treatment.

Aim

To measure RSNA in response to leptin and resistin alone and in combination, and determine the effect on the distribution of Fos in autonomic brain nuclei

Methods

RSNA, mean arterial pressure (MAP) and heart rate (HR) in anaesthetised Sprague‐Dawley male rats were recorded before and for 3 hours after intracerebroventricular saline (control, n=5), leptin (7 μg; n=5), resistin (7 μg; n=4) and the combination of both resistin and leptin (administered 15 minutes after resistin,n=6). At the end of the experiment the animals were perfused with 4% paraformaldehyde and immunohistochemistry was performed on brain sections.

Results

Leptin alone and resistin alone significantly increased RSNA (74±17%, 50±14% respectively) (P<0.0001 from saline). When resistin and leptin were combined there was a significantly greater increase in RSNA (163±23%; P<0.0001, compared to either drug alone). Changes in MAP and HR from pre‐drug levels were not significantly different between groups. The distribution of Fos‐positive cell nuclei elicited by resistin was similar to leptin. When leptin and resistin were combined, the increase in the number of Fos‐positive neurons in the arcuate nucleus, and in the lamina terminalis, was significantly greater than control.

Conclusion

The findings show that leptin and resistin, combined, enhance RSNA as well as Fos production in the arcuate nucleus and lamina terminalis. Since leptin makes an important contribution to the elevated RSNA observed in obese / overweight conditions, the increased leptin and resistin levels may mean the contribution of leptin to the elevated RSNA in those conditions is enhanced.
The Inwardly Rectifying Potassium Channel GIRK4 Plays a Role in Aldosterone Production in The Mouse Adrenal Cortex
Authors: Hardege Iris , O'Shaughnessy Kevin M
Published: November 2023

Objective

Determine the role of wild‐type GIRK4 in the mouse adrenal in relation to Aldosterone regulation.

Aldosterone plays a key role in salt homeostasis and blood pressure, its dysregulation accounts for up to 10% of hypertension. Significant portions of these cases are caused by aldosterone producing adenomas (APAs) of the adrenal cortex, and have been shown to harbour mutations in the inwardly rectifying potassium channel GIRK4. Expression of GIRK4 has since been shown in the aldosterone producing zona glomerulosa (ZG) cells of the adrenal cortex. Although the role of these mutant GIRK4 channels have been well studied in vitro, little is known about the role of wild‐type GIRK4 in vivo. Here we utilize the GIRK4 −/− mouse to investigate the role of GIRK4 in aldosterone regulation and blood pressure.

Typically aldosterone secretion from the ZG cells of the adrenal cortex is mediated by depolarization upon stimulation with angiotensin II. The presence of GIRK4 in ZG cells is thought to help maintain a hyperpolarized membrane potential post stimulation, and reduce spontaneous depolarization, thereby preventing autonomous aldosterone production.

Paradoxically our pilot data has shown a decrease in CYP11B2 gene expression (1.82 fold, P<0.05) and plasma aldosterone levels (1.63 fold, P<0.05) in GIRK4 −/− mice compared to wild‐type animals (Figure). This suggests cells lacking GIRK4 maintain a hyperpolarized membrane potential, and hence GIRK4 is not solely responsible for hyperpolarization of the ZG cells of the adrenal cortex.

In order to elucidate the molecular basis for this observation, we are conducting RNAseq analysis of adrenals from wild‐type and GIRK4 −/− mice. This will reveal transcriptomic changes that may explain the observed decrease in aldosterone production, as well as other potential pathways involved in aldosterone regulation in the adrenal cortex.

Support or Funding Information

This work was supported by the British Heart Foundation (PhD studentship to IH FS 12/78/29875)
Ventricular disfunction induces morphofunctional changes in adrenal glands
Authors: de Andrade Thúlio Ramos , Silva Juliane , Souza Leandro , Jordão Camila , Ferreira Tatiane , Negrao Carlos , Brum Patricia , Irigoyen Maria Claudia , Lacchini Silvia , Alves Maria Janieire
Published: November 2023

Objectives

To assess whether ventricular dysfunction (VD) can influence the weight and morphology of adrenal gland in rats with and without deprivation of ovarian hormones.

Methods

Female rats of the Sprague Dawley strain (60 days old) randomly divided into 4 groups: intact ovaries + IM SHAM surgery (INT+SHAM, n = 9); Intact ovaries + VD after MI (INT+DV, n = 5); Ovariectomized + MI SHAM surgery (OVX+SHAM, n = 5), and Ovariectomized + VD after MI (OVX+VD, n = 5). The ejection fraction (EF) was assessed by echocardiography, it was considered VD when EF≤55%. The surgical procedure for myocardial infarction (MI) or SHAM was performed 30 days after OVX. Eight weeks after MI the EF was measured and after 12 weeks the animals were weighed and euthanized. The adrenals, were weighed (and this value corrected by body weight), were then processed histologically and the slices stained with H‐E. The photomicrographs were analyzed by Axion Vision® software, and the thickness of each zone of the adrenal cortex, the area of medulla and gland were measured. The results were expressed as mean±standard deviation, passed through 1 way ANOVA and considered significant if p≤0.05.

Results

Body weight (g) in groups INT+SHAM (318±18.5) and INT+VD (292±16.7) were similar and smaller than OVX+SHAM (368±30.7) and OVX+VD (372±44.3). The relative weight of the adrenal gland (%) was similar between groups INT+SHAM (0.017±0) and INT+VD (0.019±0) and higher, when compared to groups OVX+SHAM (0.013±0) and OVX+VD (0.011±0) ‐ there was no difference between the relative weight of adrenal glands of OVX+VD and OVX+SHAM groups. The thickness of glomerular zone (mm) was similar in OVX +SHAM (68.68±2.9) and OVX+VD (63.1±2.9) and higher than INT+SHAM (55.35±3.5); the OVX SHAM group (68.68±2.9) was higher than INT+VD (61.02±6.3). The thickness of the reticulated area was higher in INT+SHAM (311.1±49.5) when compared to groups INT+VD (234.8±23.7), OVX+SHAM (240.2±32.3) and OVX+DV (233.1±44.09) and similar between these. The medulla/total area ratio (%) was similar between INT+SHAM (0.090±0.01) and OVX+SHAM (0.091±0.01), and lower than INT+VD group (0.120±0.02) and OVX+VD (0.124±0.02) groups.

Conclusion

The results show that the VD was efficient to induce morphological changes in adrenal gland.