bluuebunny/crossref_metadata_2025 huggingface dataset:
THE NEUROBIOLOGY OF THE ASCIDIAN TADPOLE LARVA: Recent Developments in an Ancient Chordate
Authors: Meinertzhagen Ian A. , Lemaire Patrick , Okamura Yasushi
Published: June 2004

▪ Abstract  With little more than 330 cells, two thirds within the sensory vesicle, the CNS of the tadpole larva of the ascidian Ciona intestinalis provides us with a chordate nervous system in miniature. Neurulation, neurogenesis and its genetic bases, as well as the gene expression territories of this tiny constituency of cells all follow a chordate plan, giving rise in some cases to frank structural homologies with the vertebrate brain. Recent advances are fueled by the release of the genome and EST expression databases and by the development of methods to transfect embryos by electroporation. Immediate prospects to test the function of neural genes are based on the isolation of mutants by classical genetics and insertional mutagenesis, as well as by the disruption of gene function by morpholino antisense oligo-nucleotides. Coupled with high-speed video analysis of larval swimming, optophysiological methods offer the prospect to analyze at single-cell level the function of a CNS built on a vertebrate plan.
LPS-induced downregulation of MRP2 and BSEP in human liver is due to a posttranscriptional process
Authors: Elferink Marieke G. L. , Olinga Peter , Draaisma Annelies L. , Merema Marjolijn T. , Faber Klaas Nico , Slooff Maarten J. H. , Meijer Dirk K. F. , Groothuis Geny M. M.
Published: June 2004

Endotoxin-induced cholestasis in rodents is caused by hepatic downregulation of transporters, including the basolateral Na+-dependent taurocholate transporter (ntcp) and the canalicular bile salt export pump (bsep) and multidrug resistance-associated protein 2 (mrp2). Details about the regulation of the human transporter proteins during this process are lacking. We used precision-cut human and rat liver slices to study the regulation of transporter expression during LPS-induced cholestasis. We investigated the effect of LPS on nitrate/nitrite and cytokine production in relation to the expression of inducible nitric oxide synthase, NTCP, BSEP, and MRP2 both at the level of mRNA with RT-PCR and protein using immunofluorescence microscopy. In liver slices from both species, LPS-induced expression of inducible nitric oxide synthase was detected within 1–3 h and remained increased over 24 h. In rat liver slices, this was accompanied by a significant decrease of rat ntcp and mrp2 mRNA levels, whereas bsep levels were not affected. These results are in line with previous in vivo studies and validate our liver slice technique. In LPS-treated human liver slices, NTCP mRNA was downregulated and showed an inverse correlation with the amounts of TNF-α and Il-1β produced. In contrast, MRP2 and BSEP mRNA levels were not affected under these conditions. However, after 24-h LPS challenge, both proteins were virtually absent in human liver slices, whereas marker proteins remained detectable. In conclusion, we show that posttranscriptional mechanisms play a more prominent role in LPS-induced regulation of human MRP2 and BSEP compared with the rat transporter proteins.
Pancreatic trypsin cleaves intestinal alkaline sphingomyelinase from mucosa and enhances the sphingomyelinase activity
Authors: Wu Jun , Liu Fuli , Nilsson Åke , Duan Rui-Dong
Published: June 2004

Sphingomyelin (SM) hydrolysis in the gut has implications in colonic tumorigenesis and cholesterol absorption. It is triggered by intestinal alkaline sphingomyelinase (Alk-SMase) that is present in the intestinal mucosa and content. The mechanism by which the enzyme is released into the lumen is not clear. We studied whether trypsin can dissociate Alk-SMase from the mucosa and affect its activity. During luminal perfusion of rat intestine, addition of trypsin to the buffer increased Alk-SMase activity in the perfusate output by about threefold. Treating COS-7 cells transfected with Alk-SMase cDNA with trypsin increased the SMase activity in the medium and reduced that in the cell lysate dose dependently. The appearance of Alk-SMase in the perfusate and culture medium was confirmed by Western blot analysis. The effect of trypsin was blocked by trypsin inhibitor, and neither chymotrypsin nor elastase had a similar effect. We also expressed the full length and COOH-terminal truncated Alk-SMase in COS-7 cells and found that the activity of the full-length enzyme is mainly in the cells, whereas that of the truncated form is mainly in the medium. Both forms were active, but only the activity of the full-length Alk-SMase was enhanced by trypsin. By linking a poly-His tag to the constructed cDNA, we found that the first tryptic site Arg440 upstream of the signal anchor was attacked by trypsin. In conclusion, trypsin cleaves the Alk-SMase at the COOH terminal, releases it from mucosa, and meanwhile enhances its activity. The findings indicate a physiological role of trypsin in SM digestion.
KCl evokes contraction of airway smooth muscle via activation of RhoA and Rho-kinase
Authors: Janssen Luke J. , Tazzeo Tracy , Zuo Jianmin , Pertens Evi , Keshavjee Shaf
Published: June 2004

Airway smooth muscle (ASM) cells express voltage-dependent Ca2+channels, primarily of the L-subtype. These may play a role in excitation-contraction coupling of ASM, although other signaling pathways may also contribute: one of these includes Rho and its downstream effector molecule Rho-associated kinase (ROCK). Although voltage-dependent Ca2+influx and Rho/ROCK signaling have traditionally been viewed as entirely separate pathways, recent evidence in vascular smooth muscle suggest differently. In this study, we monitored contractile activity (muscle baths) in bronchial and/or tracheal preparations from the pig, cow, and human, and further examined Rho and ROCK activities (Western blots and kinase assays) and cytosolic levels of Ca2+(fluo 4-based fluorimetry) in porcine tracheal myocytes. KCl evoked substantial contractions that were suppressed in tracheal preparations by removal of external Ca2+or using the selective L-type Ca2+channel blocker nifedipine; porcine bronchial preparations were much less sensitive, and bovine bronchi were essentially unaffected by 1 μM nifedipine. Surprisingly, KCl-evoked contractions were also highly sensitive to two structurally different ROCK inhibitors: Y-27632 and HA-1077. Furthermore, the inhibitory effects of nifedipine and of the ROCK inhibitors were not additive. KCl also caused marked stimulation of Rho and ROCK activities, and both these changes were suppressed by nifedipine or by removal of external Ca2+. KCl-induced elevation of [Ca2+]iwas not affected by Y-27632 but was reversed by NiCl2or by BAPTA-AM. We conclude that KCl acts in part through stimulation of Rho and ROCK, possibly secondary to voltage-dependent Ca2+influx.
Impact of microvascular circulation on peripheral lung stability
Authors: Peták Ferenc , Babik Barna , Hantos Zoltán , Morel Denis R. , Pache Jean-Claude , Biton Catherine , Suki Béla , Habre Walid
Published: June 2004

The involvement of pulmonary circulation in the mechanical properties was studied in isolated rat lungs. Pulmonary input impedance (ZL) was measured at a mean transpulmonary pressure (Ptpmean) of 2 cmH2O before and after physiological perfusion with either blood or albumin. In these lungs and in a group of unperfused lungs, ZL was also measured at Ptpmean values between 1 and 8 cmH2O. Airway resistance ( Raw) and parenchymal damping (G) and elastance (H) were estimated from ZL. End-expiratory lung volume (EELV) was measured by immersion before and after blood perfusion. The orientation of the elastin fibers relative to the basal membrane was assessed in additional unperfused and blood-perfused lungs. Pressurization of the pulmonary capillaries significantly decreased H by 31.5 ± 3.7% and 18.7 ± 2.7% for blood and albumin, respectively. Perfusion had no effect on Raw but markedly altered the Ptpmean dependences of G and H <4 cmH2O, with significantly lower values than in the unperfused lungs. At a Ptpmean of 2 cmH2O, EELV increased by 31 ± 11% ( P = 0.01) following pressurization of the capillaries, and the elastin fibers became more parallel to the basal membrane. Because the organization of elastin fibers results in smaller H values of the individual alveolus, the higher H in the unperfused lungs is probably due to a partial alveolar collapse leading to a loss in lung volume. We conclude that the physiological pressure in the pulmonary capillaries is an important mechanical factor in the maintenance of the stability of the alveolar architecture.
Membrane-specific expression of functional purinergic receptors in normal human nasal epithelial cells
Authors: Kim Chang-Hoon , Kim Sung-Shik , Choi Jae Young , Shin Ji-Hyun , Kim Jin Young , Namkung Wan , Lee Jeung-Gweon , Lee Min Goo , Yoon Joo-Heon
Published: June 2004

Extracellular purines and pyrimidines regulate various physiological responses via the cell surface receptors known as purinoreceptors and may exert autocrine or paracrine effects on ion transport, fluid transport, ciliary beat frequency, and mucin secretion. Therefore, this study aims to investigate the expression patterns of the purinoreceptors in normal human nasal epithelial (NHNE) cells. In RT-PCR, the mRNAs for several P2X (P2X3, P2X4, P2X7) and P2Y (P2Y1, P2Y2, P2Y4, P2Y6, P2Y11, P2Y12) receptors were identified in NHNE cells. Functional localizations of P2 receptors were investigated by measuring intracellular calcium concentration ([Ca2+]i) increases in membrane-specific manner using a double-perfusion chamber. Absence of the responses of αβ-methylene ATP and 2-methylthio-ATP excluded functionally active P2X3, P2X4, and P2Y1 receptors as far as [Ca2+]i increase is concerned. Applications with ATP and UTP revealed that luminal membranes of NHNE cells express P2Y2 and P2Y6 receptors and basolateral membranes express P2Y2 receptor. Expressions of P2Y2 and P2Y6 receptors in NHNE cells were further verified by immunoblotting using specific antibodies. In addition, the results with 2,3-O-(4-benzoyl)-benzoyl-ATP indicate that the P2Y11 receptor may be present on the luminal side. In conclusion, the NHNE cells express functionally active P2Y2, P2Y6, and P2Y11 receptors in a membrane-specific pattern, which may play an important role in the control of mucin and fluid secretion in NHNE cells.
cAMP-stimulated Na+transport in H441 distal lung epithelial cells: role of PKA, phosphatidylinositol 3-kinase, and sgk1
Authors: Thomas Christie P. , Campbell Jason R. , Wright Patrick J. , Husted Russell F.
Published: June 2004

H441 cells, a bronchiolar epithelial cell line, develop a cAMP-regulated benzamil-sensitive Na+transport pathway on permeable supports (Itani OA, Auerbach SD, Husted RF, Volk KA, Ageloff S, Knepper MA, Stokes JB, Thomas CP. Am J Physiol Lung Cell Mol Physiol 282: L631–L641, 2002). To understand the molecular basis for the stimulation of Na+transport, we delineated the role of specific intracellular pathways and examined the effect of cAMP on αβγ-epithelial Na+channel (ENaC) and sgk1 expression. Na+transport increases within 5 min of cAMP stimulation and is sustained for >24 h. The sustained effect of cAMP on Na+transport is abolished by LY-294002, an inhibitor of phosphatidylinositol 3-kinase, by H89, an inhibitor of PKA, or by SB-202190, an inhibitor of p38 MAP kinase. The sustained effect of cAMP was associated with increases in α-ENaC mRNA and protein but without a detectable increase in βγ-ENaC and sgk1. The early effect of cAMP on Na+transport is brefeldin sensitive and is mediated via PKA. These results are consistent with a model where the early effect of cAMP is to increase trafficking of Na+channels to the apical cell surface whereas the sustained effect requires the synthesis of α-ENaC.
Acute hypotension induced by aortic clamp vs. PTH provokes distinct proximal tubule Na+transporter redistribution patterns
Authors: Leong Patrick K. K. , Yang Li E. , Lin Harrison W. , Holstein-Rathlou Niels H. , McDonough Alicia A.
Published: June 2004

Renal parathyroid hormone (PTH) action is often studied at high doses (100 μg PTH/kg) that lower mean arterial pressure significantly, albeit transiently, complicating interpretation of studies. Little is known about the effect of acute hypotension on proximal tubule Na+transporters. This study aimed to determine the effects of acute hypotension, induced by aortic clamp or by high-dose PTH (100 μg PTH/kg), on renal hemodynamics and proximal tubule Na/H exchanger isoform 3 (NHE3) and type IIa Na-Picotransporter protein (NaPi2) distribution. Subcellular distribution was analyzed in renal cortical membranes fractionated on sorbitol density gradients. Aortic clamp-induced acute hypotension (from 100 ± 3 to 78 ± 2 mmHg) provoked a 62% decrease in urine output and a significant decrease in volume flow from the proximal tubule detected as a 66% decrease in endogenous lithium clearance. There was, however, no significant change in glomerular filtration rate (GFR) or subcellular distribution of NHE3 and NaPi2. In contrast, high-dose PTH rapidly (<2 min) decreased arterial blood pressure to 51 ± 3 mmHg, decreased urine output, and shifted NHE3 and NaPi2 out of the low-density membranes enriched in apical markers. PTH at much lower doses (<1.4 μg·kg−1·h−1) did not change blood pressure and was diuretic. In conclusion, acute hypotension per se increases proximal tubule Na+reabsorption without changing NHE3 or NaPi2 subcellular distribution, indicating that trafficking of transporters to the surface is not the likely mechanism; in comparison, hypotension secondary to high-dose PTH blocks the primary diuretic effect of PTH but does not inhibit the PTH-stimulated redistribution of NHE3 and NaPi2 to the base of the microvilli.
Descending vasomotor pathways from the dorsomedial hypothalamic nucleus: role of medullary raphe and RVLM
Authors: Horiuchi J. , McAllen R. M. , Allen A. M. , Killinger S. , Fontes M. A. P. , Dampney R. A. L.
Published: June 2004

The dorsomedial hypothalamic nucleus (DMH) is believed to play a key role in mediating vasomotor and cardiac responses evoked by an acute stress. Inhibition of neurons in the rostral ventrolateral medulla (RVLM) greatly reduces the increase in renal sympathetic nerve activity (RSNA) evoked by activation of the DMH, indicating that RVLM neurons mediate, at least in part, the vasomotor component of the DMH-evoked response. In this study, the first aim was to determine whether neurons in the medullary raphe pallidus (RP) region also contribute to the DMH-evoked vasomotor response, because it has been shown that the DMH-evoked tachycardia is mediated by the RP region. The second aim was to directly assess the effect of DMH activation on the firing rate of RVLM sympathetic premotor neurons. In urethane-anesthetized rats, injection of the GABAA receptor agonist muscimol (but not vehicle solution) in the RP region caused a modest (∼25%) but significant reduction in the increase in RSNA evoked by DMH disinhibition (by microinjection of bicuculline). In other experiments, disinhibition of the DMH resulted in a powerful excitation (increase in firing rate of ∼400%) of 5 out of 6 spinally projecting barosensitive neurons in the RVLM. The results indicate that neurons in the RP region make a modest contribution to the renal sympathoexcitatory response evoked from the DMH and also that sympathetic premotor neurons in the RVLM receive strong excitatory inputs from DMH neurons, consistent with the view that the RVLM plays a key role in mediating sympathetic vasomotor responses arising from the DMH.
The viral mimic, polyinosinic:polycytidylic acid, induces fever in rats via an interleukin-1-dependent mechanism
Authors: Fortier Marie-Eve , Kent Stephen , Ashdown Helen , Poole Stephen , Boksa Patricia , Luheshi Giamal N.
Published: June 2004

Polyinosinic:polycytidylic acid (poly I:C) is a synthetic double-stranded RNA that is used experimentally to model viral infections in vivo. Previous studies investigating the inflammatory properties of this agent in rodents demonstrated that it is a potent pyrogen. However, the mechanisms underlying this response have not been fully elucidated. In the current study, we examined the effects of peripheral administration of poly I:C on body temperature and cytokine production. Male rats were implanted with biotelemetry devices and randomly assigned to one of the following three groups: poly I:C + saline, poly I:C + interleukin-1 receptor antagonist (IL-1ra), or saline + saline. Maximal fever of 1.6°C above baseline was observed 3 h after an intraperitoneal injection of poly I:C (750 μg/kg). Pretreatment with IL-1ra diminished this response by >50% (maximum body temperature = 0.6°C above baseline). Plasma IL-6 concentration increased fivefold 2 h post-poly I:C compared with saline-injected rats; levels returned to baseline 4 h postinjection. Pretreatment with IL-1ra prevented this rise in IL-6. Plasma tumor necrosis factor (TNF)-α was also increased more than fourfold 2 h postinjection but remained unaffected by IL-1ra treatment. IL-1β and cyclooxygenase-2 mRNA were significantly upregulated in the hypothalamus of poly I:C-treated animals. Finally, poly I:C decreased food intake by 30%, but this response was not altered by pretreatment with IL-1ra. These results suggest that poly I:C induces fever, but not anorexia, through an IL-1 and prostaglandin-dependent mechanism.
Downregulation of cGMP-dependent protein kinase-1 activity in the corpus cavernosum smooth muscle of diabetic rabbits
Authors: Chang Shaohua , Hypolite Joseph A. , Velez Marielena , Changolkar Arun , Wein Alan J. , Chacko Samuel , DiSanto Michael E.
Published: June 2004

Increased guanosine 3′,5′-cyclic monophosphate (cGMP), induced by nitric oxide release, is crucial for corpus cavernosum smooth muscle (CCSM) relaxation within the penis. This CCSM relaxation (necessary for penile erection) is impaired in men with erectile dysfunction (ED), especially those men with diabetes. One of the effector proteins for cGMP is cGMP-dependent protein kinase-1 (PKG-1). PKG-1 knockout mice exhibit detrusor overactivity ( Am J Physiol Regul Integr Comp Physiol 279: R1112–R1120, 2000) and, more relevant to this study, ED ( Proc Natl Acad Sci USA 97: 2349–2354, 2000), suggesting an in vivo role for PKG-1 in urogenital smooth muscle relaxation. In the current study, using normal rabbit CCSM, Western blot analysis revealed high expression of PKG-1 at levels almost equivalent to aorta (previously shown to have high PKG-1 expression) and that the two known alternatively spliced isoforms of PKG-1 (α and β) are expressed in nearly equal amounts in the CCSM. However, in response to alloxan-induced diabetes, there was a decrease in expression of both PKG-1 isoforms at the mRNA and protein levels as determined by real-time RT-PCR and Western blotting, respectively, but with the PKG-1α isoform expression decreased to a greater extent. Moreover, diabetes was associated with significantly decreased PKG-1 activity of CCSM in vitro, correlating with decreased CCSM relaxation. Immunofluorescence microscopy revealed a diabetes-associated decrease in PKG-1 in the CCSM cells. In conclusion, our results demonstrate for the first time a significant downregulation of PKG-1 expression associated with decreased PKG-1 activity in the CCSM in response to diabetes. Furthermore, these results suggest a mechanistic basis for the decreased efficacy of phosphodiesterase V inhibitors in treating diabetic patients with ED.
Left ventricular chamber stiffness at rest as a determinant of exercise capacity in heart failure subjects with decreased ejection fraction
Authors: Meyer Timothy E. , Karamanoglu Mustafa , Ehsani Ali A. , Kovács Sándor J.
Published: June 2004

Impaired exercise tolerance, determined by peak oxygen consumption (V̇o2 peak), is predictive of mortality and the necessity for cardiac transplantation in patients with chronic heart failure (HF). However, the role of left ventricular (LV) diastolic function at rest, reflected by chamber stiffness assessed echocardiographically, as a determinant of exercise tolerance is unknown. Increased LV chamber stiffness and limitation of V̇o2 peak are known correlates of HF. Yet, the relationship between chamber stiffness and V̇o2 peak in subjects with HF has not been fully determined. Forty-one patients with HF New York Heart Association [(NYHA) class 2.4 ± 0.8, mean ± SD] had echocardiographic studies and V̇o2 peak measurements. Transmitral Doppler E waves were analyzed using a previously validated method to determine k, the LV chamber stiffness parameter. Multiple linear regression analysis of V̇o2 peak variance indicated that LV chamber stiffness k ( r2 = 0.55) and NYHA classification ( r2 = 0.43) were its best independent predictors and when taken together account for 59% of the variability in V̇o2 peak. We conclude that diastolic function at rest, as manifested by chamber stiffness, is a major determinant of maximal exercise capacity in HF.
Fatiguing exercise reduces DNA binding activity of NF-κB in skeletal muscle nuclei
Authors: Durham William J. , Li Yi-Ping , Gerken Eric , Farid Mehran , Arbogast Sandrine , Wolfe Robert R. , Reid Michael B.
Published: June 2004

This study tested the hypothesis that skeletal muscle contraction activates nuclear factor-κB (NF-κB), a putative regulator of muscle protein breakdown. Muscle biopsies were obtained from the vastus lateralis of healthy humans before, immediately after, and 1 h after fatiguing resistance exercise of the lower limbs. Biopsies were analyzed for nuclear NF-κB DNA binding activity by using electrophoretic mobility shift assay. NF-κB activity, measured immediately after exercise, was less than preexercise activity; after 1-h recovery, activity returned to preexercise levels. In follow-up studies in adult mice, basal NF-κB activity varied among individual muscles. NF-κB activity in diaphragm fiber bundles was decreased after a 10-min bout of fatiguing tetanic contractions in vitro. NF-κB activity in soleus was increased by 12 days of unloading by hindlimb suspension; this increase was reversed by 10 min of fatiguing exercise. These data provide no support for our original hypothesis. Instead, acute fatiguing exercise appears to decrease NF-κB activity in muscle under a variety of conditions.
Biphasic effect of hydrogen peroxide on skeletal muscle arteriolar tone via activation of endothelial and smooth muscle signaling pathways
Authors: Csekő Csongor , Bagi Zsolt , Koller Akos
Published: June 2004

We hypothesized that hydrogen peroxide (H2O2) has a role in the local regulation of skeletal muscle blood flow, thus significantly affecting the myogenic tone of arterioles. In our study, we investigated the effects of exogenous H2O2 on the diameter of isolated, pressurized (at 80 mmHg) rat gracilis skeletal muscle arterioles (diameter of ∼150 μm). Lower concentrations of H2O2 (10−6–3 × 10−5 M) elicited constrictions, whereas higher concentrations of H2O2 (6 × 10−5–3 × 10−4 M), after initial constrictions, caused dilations of arterioles (at 10−4 M H2O2, −19 ± 1% constriction and 66 ± 4% dilation). Endothelium removal reduced both constrictions (to −10 ± 1%) and dilations (to 33 ± 3%) due to H2O2. Constrictions due to H2O2 were completely abolished by indomethacin and the prostaglandin H2/thromboxane A2 (PGH2/TxA2) receptor antagonist SQ-29548. Dilations due to H2O2 were significantly reduced by inhibition of nitric oxide synthase (to 38 ± 7%) but were unaffected by clotrimazole or sulfaphenazole (inhibitors of cytochrome P-450 enzymes), indomethacin, or SQ-29548. In endothelium-denuded arterioles, clotrimazole had no effect, whereas H2O2-induced dilations were significantly reduced by charybdotoxin plus apamin, inhibitors of Ca2+-activated K+ channels (to 24 ± 3%), the selective blocker of ATP-sensitive K+ channels glybenclamide (to 14 ± 2%), and the nonselective K+-channel inhibitor tetrabutylammonium (to −1 ± 1%). Thus exogenous administration of H2O2 elicits 1) release of PGH2/TxA2 from both endothelium and smooth muscle, 2) release of nitric oxide from the endothelium, and 3) activation of K+ channels, such as Ca2+-activated and ATP-sensitive K+ channels in the smooth muscle resulting in biphasic changes of arteriolar diameter. Because H2O2 at low micromolar concentrations activates several intrinsic mechanisms, we suggest that H2O2 contributes to the local regulation of skeletal muscle blood flow in various physiological and pathophysiological conditions.
Hemodynamics and O2 uptake during maximal knee extensor exercise in untrained and trained human quadriceps muscle: effects of hyperoxia
Authors: Mourtzakis M. , González-Alonso J. , Graham T. E. , Saltin B.
Published: June 2004

To elucidate the potential limitations on maximal human quadriceps O2 capacity, six subjects trained (T) one quadriceps on the single-legged knee extensor ergometer (1 h/day at 70% maximum workload for 5 days/wk), while their contralateral quadriceps remained untrained (UT). Following 5 wk of training, subjects underwent incremental knee extensor tests under normoxic (inspired O2 fraction = 21%) and hyperoxic (inspired O2 fraction = 60%) conditions with the T and UT quadriceps. Training increased quadriceps muscle mass (2.9 ± 0.2 to 3.1 ± 0.2 kg), but did not change fiber-type composition or capillary density. The T quadriceps performed at a greater peak power output than UT, under both normoxia (101 ± 10 vs. 80 ± 7 W; P < 0.05) and hyperoxia (97 ± 11 vs. 81 ± 7 W; P < 0.05) without further increases with hyperoxia. Similarly, thigh peak O2 consumption, blood flow, vascular conductance, and O2 delivery were greater in the T vs. the UT thigh (1.4 ± 0.2 vs. 1.1 ± 0.1 l/min, 8.4 ± 0.8 vs. 7.2 ± 0.8 l/min, 42 ± 6 vs. 35 ± 4 ml·min−1·mmHg−1, 1.71 ± 0.18 vs. 1.51 ± 0.15 l/min, respectively) but were not enhanced with hyperoxia. Oxygen extraction was elevated in the T vs. the UT thigh, whereas arteriovenous O2 difference tended to be higher (78 ± 2 vs. 72 ± 4%, P < 0.05; 160 ± 8 vs. 154 ± 11 ml/l, respectively; P = 0.098) but again were unaltered with hyperoxia. In conclusion, the present results demonstrate that the increase in quadriceps muscle O2 uptake with training is largely associated with increases in blood flow and O2 delivery, with smaller contribution from increases in O2 extraction. Furthermore, the elevation in peak muscle blood flow and vascular conductance with endurance training seems to be related to an enhanced vasodilatory capacity of the vasculature perfusing the quadriceps muscle that is unaltered by moderate hyperoxia.
Lung-targeted VEGF inactivation leads to an emphysema phenotype in mice
Authors: Tang Kechun , Rossiter Harry B. , Wagner Peter D. , Breen Ellen C.
Published: June 2004

To test the hypothesis that VEGF is important for the maintenance of alveolar structure and elastic properties in adult mice, lung-targeted ablation of the VEGF gene was accomplished through intratracheal delivery of an adeno-associated cre recombinase virus (AAV/Cre) to VEGF loxP mice, and the effects were followed for 8 wk. Control mice were similarly treated with AAV/Cre. Pulmonary VEGF levels were reduced by 86% at 5 wk postinfection but returned to normal levels by 8 wk. VEGF receptor VEGFR-2 levels were also reduced at 5 wk (by 51%) and returned to control values by 8 wk. However, alveolar septal wall destruction (increased mean linear intercept) and loss of lung elastic recoil (increased compliance) persisted for 8 wk. No decrease in alveolar cell proliferation was detected by Western blot or immunohistochemical analysis of proliferating cell nuclear antigen. Increased alveolar septal cell and bronchial epithelial cell apoptosis was detected by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling analysis at 5 wk. Total lung caspase-3 levels and enzyme activity were also increased at 5 wk. No obvious accumulation of inflammatory cells was observed at any time after tracheal instillation of AAV/Cre. Thus a transient decrease in pulmonary VEGF leads to increased alveolar and bronchial cell apoptosis, air space enlargement, and changes in lung elastic recoil (processes that are characteristic of emphysema) that persist for at least 8 wk.
Endothelial function in coronary arterioles from pigs with early-stage coronary disease induced by high-fat, high-cholesterol diet: effect of exercise
Authors: Henderson Kyle K. , Turk James R. , Rush James W. E. , Laughlin M. Harold
Published: June 2004

Because hypercholesterolemia can attenuate endothelial function and exercise training can augment endothelial function, we hypothesized that exercise training would improve endothelial function of coronary arterioles from pigs in the early stages of cardiovascular disease induced by a high-fat, high-cholesterol (HF) diet. Yucatan miniature swine were fed a normal-fat (NF) diet or HF diet (2% cholesterol) for 20 wk in which 8 and 46% of their calories were derived from fat, respectively. Both groups were subdivided into sedentary (Sed) or exercise-trained (Ex) groups. This resulted in four experimental groups: NFSed, NFEx, HFSed, and HFEx. Endothelial function was assessed in coronary arterioles 75–100 μm in diameter dissected from the left ventricular apex. Responses to endothelial-dependent dilation induced by bradykinin (BK), ADP, and flow were similar in all four groups, whereas dilation to aggregating platelets in the presence of indomethacin and ketanserin was attenuated in HFSed arterioles ( P = 0.01). The attenuated response to aggregating platelets was prevented or reversed in HFEx arterioles ( P = 0.03). In HFSed arterioles, BK induced release of an indomethacin-sensitive prostanoid constrictor. In contrast, after exercise training, there was no evidence of this constrictor and BK-induced release of an indomethacin-sensitive prostanoid dilator in HFEx arterioles ( P = 0.04). Endothelial nitric oxide synthase protein in arterioles was significantly reduced in HF groups ( P < 0.05) and increased in Ex groups ( P < 0.05). Interestingly, the relative contribution of nitric oxide to BK-induced dilation, as assessed with nitro-l-arginine methyl ester, was similar in arterioles in the NF, HF, Sed, and Ex groups. These results suggest that, in the early stages of cardiovascular disease, a high-fat, high-cholesterol diet has modest effects on endothelial-dependent dilation in coronary arterioles; nonetheless, these effects are prevented or reversed with exercise training.
Exercise alters the profile of phospholipid molecular species in rat skeletal muscle
Authors: Mitchell Todd W. , Turner Nigel , Hulbert A. J. , Else Paul L. , Hawley John A. , Lee Jong Sam , Bruce Clinton R. , Blanksby Stephen J.
Published: June 2004

We have determined the effect of two exercise-training intensities on the phospholipid profile of both glycolytic and oxidative muscle fibers of female Sprague-Dawley rats using electrospray-ionization mass spectrometry. Animals were randomly divided into three training groups: control, which performed no exercise training; low-intensity (8 m/min) treadmill running; or high-intensity (28 m/min) treadmill running. All exercise-trained rats ran 1,000 m/session for 4 days/wk for 4 wk and were killed 48 h after the last training bout. Exercise training was found to produce no novel phospholipid species but was associated with significant alterations in the relative abundance of a number of phospholipid molecular species. These changes were more prominent in glycolytic (white vastus lateralis) than in oxidative (red vastus lateralis) muscle fibers. The largest observed change was a decrease of ∼20% in the abundance of 1-stearoyl-2-docosahexaenoyl-phosphatidylethanolamine [PE(18:0/22:6); P < 0.001] ions in both the low- and high-intensity training regimes in glycolytic fibers. Increases in the abundance of 1-oleoyl-2-linoleoyl phopshatidic acid [PA(18:1/18:2); P < 0.001] and 1-alkenylpalmitoyl-2-linoleoyl phosphatidylethanolamine [plasmenyl PE (16:0/18:2); P < 0.005] ions were also observed for both training regimes in glycolytic fibers. We conclude that exercise training results in a remodeling of phospholipids in rat skeletal muscle. Even though little is known about the physiological or pathophysiological role of specific phospholipid molecular species in skeletal muscle, it is likely that this remodeling will have an impact on a range of cellular functions.
Relationships between maximal muscle oxidative capacity and blood lactate removal after supramaximal exercise and fatigue indexes in humans
Authors: Thomas C. , Sirvent P. , Perrey S. , Raynaud E. , Mercier J.
Published: June 2004

The present study investigated whether blood lactate removal after supramaximal exercise and fatigue indexes measured during continuous and intermittent supramaximal exercises are related to the maximal muscle oxidative capacity in humans with different training status. Lactate recovery curves were obtained after a 1-min all-out exercise. A biexponential time function was then used to determine the velocity constant of the slow phase (γ2), which denoted the blood lactate removal ability. Fatigue indexes were calculated during all-out (FIAO) and repeated 10-s cycling sprints (FISprint). Biopsies were taken from the vastus lateralis muscle, and maximal ADP-stimulated mitochondrial respiration ( Vmax) was evaluated in an oxygraph cell on saponin-permeabilized muscle fibers with pyruvate + malate and glutamate + malate as substrates. Significant relationships were found between γ2 and pyruvate + malate Vmax ( r = 0.60, P < 0.05), γ2 and glutamate + malate Vmax ( r = 0.66, P < 0.01), and γ2 and citrate synthase activity ( r = 0.76, P < 0.01). In addition, γ2, glutamate + malate Vmax, and pyruvate + malate Vmax were related to FIAO (γ2 − FIAO: r = 0.85; P < 0.01; glutamate + malate Vmax − FIAO: r = 0.70, P < 0.01; and pyruvate + malate Vmax − FIAO: r = 0.63, P < 0.01) and FISprint (γ2 − FISprint: r = 0.74, P < 0.01; glutamate + malate Vmax − FISprint: r = 0.64, P < 0.01; and pyruvate + malate Vmax − FISprint: r = 0.46, P < 0.01). In conclusion, these results suggested that the maximal muscle oxidative capacity was related to blood lactate removal ability after a 1-min all-out test. Moreover, maximal muscle oxidative capacity and blood lactate removal ability were associated with the delay in the fatigue observed during continuous and intermittent supramaximal exercises in well-trained subjects.
Regional lung growth following pneumonectomy assessed by computed tomography
Authors: Ravikumar Priya , Yilmaz Cuneyt , Dane D. Merrill , Johnson Robert L. , Estrera Aaron S. , Hsia Connie C. W.
Published: June 2004

After pneumonectomy (PNX), mechanical strain on the remaining lung is greatly increased. To assess whether remaining lobes expand uniformly after left or right PNX (removing 42 and 58% of lung mass, respectively), we performed high-resolution computed tomography (CT) scans at 45 ml/kg above end-expiratory lung volume on adult male foxhounds after left or right PNX, which were compared with adult Sham controls. Air and tissue volumes were separately measured in each lobe. After left PNX, air and tissue volumes in the right upper and cardiac lobes increased ∼2.2-fold above and below the heart, whereas volumes in right middle and lower lobes did not change significantly. After right PNX, air and tissue volumes in the left upper and middle lobes increased 2.3- to 2.7-fold across the midline anterior to the heart, whereas the left lower lobe expanded ∼1.9-fold posterior to the heart. Regional changes in volume density of tissue post-PNX estimated by CT scan parallel postmortem estimates by morphometric analyses. Data indicate heterogeneous regional distribution of mechanical lung strain, which could influence the differential cellular compensatory response following right and left PNX.
Comparison of PEG-modified albumin and hemoglobin in extreme hemodilution in the rat
Authors: Winslow Robert M. , Lohman Jeff , Malavalli Ashok , Vandegriff Kim D.
Published: June 2004

We have reported a new polyethylene glycol (PEG)-modified, hemoglobin-based O2 carrier (MP4) with novel properties, including a large molecular excluded volume and low Po2 necessary to obtain 50% O2 (∼6 Torr). To evaluate the ability of MP4 to transport O2, we compared it with PEG-modified albumin (MPA) using the identical chemistry of attachment of PEG chains. The resulting solutions were well matched with respect to all physical properties except that MP4 is an O2 carrier, whereas MPA is not. An additional solution, 10% pentastarch, was matched with the PEG-modified proteins with regard to oncotic activity and viscosity but does not contain PEG. The model used to evaluate O2 transport was continuous exchange transfusion in the rat until the hematocrit was virtually unmeasureable. Objective end points included survival and the onset of anaerobic metabolism, signaled by acid-base derangement and accumulation of lactic acid. Continuous exchange transfusion of 2.5 blood volumes in rats ( n = 5 in each treatment group) was carried out over 60 min, such that the final hematocrit was between 0 and 5% in all animals. Animals were observed for an additional 70 min, when survivors were killed. Overall survival for the MP4 animals was 100%; no animal that received either pentastarch or MPA survived. The hematocrit at which lactic acid began to rise was ∼14.8% in both pentastarch and MPA animals and 7.4% in the animals that received MP4. In all groups, the total hemoglobin was ∼5 g/dl at this point. We conclude that, despite its low Po2 necessary to obtain 50% O2, MP4 effectively substitutes for red blood cell hemoglobin in its ability to oxygenate tissues in extreme hemodilution.
Force fluctuations are modulated by alternate muscle activity of knee extensor synergists during low-level sustained contraction
Authors: Kouzaki Motoki , Shinohara Minoru , Masani Kei , Fukunaga Tetsuo
Published: June 2004

The study examined the hypothesis that altered synergistic activation of the knee extensors leads to cyclic modulation of the force fluctuations. To test this hypothesis, the force fluctuations were investigated during sustained knee extension at 2.5% of maximal voluntary contraction force for 60 min in 11 men. Surface electromyograms (EMG) were recorded from the rectus femoris (RF), vastus lateralis (VL), and vastus medialis (VM) muscles. The SD of force and average EMG (AEMG) of each muscle were calculated for 30-s periods during alternate muscle activity. Power spectrum of force was calculated for the low- (≤3 Hz), middle- (4–6 Hz), and high-frequency (8–12 Hz) components. Alternate muscle activity was observed between RF and the set of VL and VM muscles. The SD of force was not constant but variable due to the alternate muscle activity. The SD was significantly greater during high RF activity compared with high VL and VM activity ( P < 0.05), and the correlation coefficient between the SD and AEMG was significantly greater in RF [0.736 (SD 0.095), P < 0.05] compared with VL and VM. Large changes were found in the high-frequency component. During high RF activity, the correlation coefficient between the SD and high-frequency component [0.832 (SD 0.087)] was significantly ( P < 0.05) greater compared with other frequency components. It is suggested that modulations in knee extension force fluctuations are caused by the unique muscle activity in RF during the alternate muscle activity, which augments the high-frequency component of the fluctuations.
Cerebral metabolism during upper and lower body exercise
Authors: Dalsgaard Mads K. , Volianitis Stefanos , Yoshiga Chie C. , Dawson Ellen A. , Secher Niels H.
Published: June 2004

When continuation of exercise calls for a “will,” the cerebral metabolic ratio of O2 to (glucose + lactate) decreases, with the largest reduction (30–50%) at exhaustion. Because a larger effort is required to exercise with the arms than with the legs, we tested the hypothesis that the reduction in the cerebral metabolic ratio would become more pronounced during arm cranking than during leg exercise. The cerebral arterial-venous differences for blood-gas variables, glucose, and lactate were evaluated in two groups of eight subjects during exhaustive arm cranking and leg exercise. During leg exercise, exhaustion was elicited after 25 ± 6 (SE) min, and the cerebral metabolic ratio was reduced from 5.6 ± 0.2 to 3.5 ± 0.2 after 10 min and to 3.3 ± 0.3 at exhaustion ( P < 0.05). Arm cranking lasted for 35 ± 4 min and likewise decreased the cerebral metabolic ratio after 10 min (from 6.7 ± 0.4 to 5.0 ± 0.3), but the nadir at exhaustion was only 4.7 ± 0.4, i.e., higher than during leg exercise ( P < 0.05). The results demonstrate that exercise decreases the cerebral metabolic ratio when a conscious effort is required, irrespective of the muscle groups engaged. However, the comparatively small reduction in the cerebral metabolic ratio during arm cranking suggests that it is influenced by the exercise paradigm.
Pentoxifylline reduces fibrin deposition and prolongs survival in neonatal hyperoxic lung injury
Authors: ter Horst Simone A. J. , Wagenaar Gerry T. M. , de Boer Eveline , van Gastelen Margôt A. , Meijers Joost C. M. , Biemond Bart J. , Poorthuis Ben J. H. M. , Walther Frans J.
Published: June 2004

Bronchopulmonary dysplasia is a leading cause of mortality and morbidity in preterm infants despite improved treatment modalities. Pentoxifylline, a phosphodiesterase inhibitor, inhibits multiple processes that lead to neonatal hyperoxic lung injury, including inflammation, coagulation, and edema. Using a preterm rat model, we investigated the effects of pentoxifylline on hyperoxia-induced lung injury and survival. Preterm rat pups were exposed to 100% oxygen and injected subcutaneously with 0.9% saline or 75 mg/kg pentoxifylline twice a day. On day 10, lung tissue was harvested for histology, fibrin deposition, and mRNA expression, and bronchoalveolar lavage fluid was collected for total protein concentration. Pentoxifylline treatment increased mean survival by 3 days ( P = 0.0018) and reduced fibrin deposition by 66% ( P < 0.001) in lung homogenates compared with untreated hyperoxia-exposed controls. Monocyte chemoattractant protein-1 expression in lung homogenates was decreased, but the expressions of TNF-α, IL-6, matrix metalloproteinase-12, tissue factor, and plasminogen activator inhibitor-1 were similar in both groups. Total protein concentration in bronchoalveolar lavage fluid was decreased by 33% ( P = 0.029) in the pentoxifylline group. Pentoxifylline treatment attenuates alveolar fibrin deposition and prolongs survival in preterm rat pups with neonatal hyperoxic lung injury, probably by reducing capillary-alveolar protein leakage.
Sarcomere strain and heterogeneity correlate with injury to frog skeletal muscle fiber bundles
Authors: Patel Tina J. , Das Ronnie , Fridén Jan , Lutz Gordon J. , Lieber Richard L.
Published: June 2004

Sarcomere length and first-order diffraction line width were measured by laser diffraction during elongation of activated frog tibialis anterior muscle fiber bundles (i.e., eccentric contraction) at nominal fiber strains of 10, 25, or 35% ( n = 18) for 10 successive contractions. Tetanic tension, measured just before each eccentric contraction, differed significantly among strain groups and changed dramatically during the 10-contraction treatment ( P < 0.01). Average maximum tetanic tension for the three groups measured before any treatment was 203.7 ± 6.8 kN/m2, but after the 10-eccentric contraction sequence decreased to 180.3 ± 3.8, 125.1 ± 7.8, and 78.3 ± 5.1 kN/m2for the 10, 25, and 35% strain groups, respectively ( P < 0.0001). Addition of 10 mM caffeine to the bathing medium decreased the loss of tetanic tension in the 10% strain group but had only a minimal effect on either the 25 or 35% strain groups. Diffraction pattern line width, a measure of sarcomere length heterogeneity, increased significantly with muscle activation and then continued to increase with successive stretches of the activated muscle. Line width increase after each stretch was significantly correlated with the lower yield tension of the successive contractile record. These data demonstrate a direct association and, perhaps, a causal relationship between sarcomere strain and fiber bundle injury. They also demonstrate that muscle injury is accompanied by a progressive increase in sarcomere length heterogeneity, yielding lower yield tension as injury progresses.
Ratiometric intracellular calcium imaging in the isolated beating rat heart using indo-1 fluorescence
Authors: Eerbeek Otto , Mik Egbert G. , Zuurbier Coert J. , Loo Martijn van ‘t , Donkersloot Cees , Ince Can
Published: June 2004

Abnormalities in intracellular calcium (Cai2+) handling have been implicated as the underlying mechanism in a large number of pathologies in the heart. Study into the relation between Cai2+behavior and performance of the whole heart function could provide detailed information into the cellular basis of heart function. In this study we describe an optical ratio imaging setup and an analysis method for the beat-to-beat Cai2+videofluorescence images of an indo-1 loaded, isolated Tyrode-perfused beating rat heart. The signal-to-noise ratio and the spatiotemporal resolution (with an optimum of 1 ms and 0.6 mm, respectively) made it possible to register different temporal Cai2+transients together with left ventricle pressure changes. The Cai2+transients showed that Cai2+activation propagates horizontally from left to right during sinus rhythm or from the stimulus site during direct left ventricle stimulation. The indo-1 ratiometric video technique developed allows the imaging of ratio changes of Cai2+with a high temporal (1 ms) and spatial (0.6 mm) resolution in the isolated Tyrode-perfused beating rat heart.
Effects of reduced free fatty acid availability on hormone-sensitive lipase activity in human skeletal muscle during aerobic exercise
Authors: O'Neill Marcus , Watt Matthew J. , Heigenhauser George J. F. , Spriet Lawrence L.
Published: June 2004

Hormone-sensitive lipase (HSL) catalyzes the hydrolysis of intramuscular triacylglycerol (IMTG); however, its regulation in skeletal muscle is poorly understood. To examine the effects of reduced free fatty acid (FFA) availability on HSL activity in skeletal muscle during aerobic exercise, 11 trained men exercised at 55% maximal O2uptake for 40 min after the ingestion of nicotinic acid (NA) or nothing (control). Muscle biopsies were taken at rest and 5, 20, and 40 min of exercise. Plasma FFA were suppressed ( P < 0.05) in NA during exercise (∼0.40 ± 0.04 vs. ∼0.07 ± 0.01 mM). The respiratory exchange ratio (RER) was increased throughout exercise (0.020 + 0.008) after NA ingestion. However, the provision of energy from fat oxidation only decreased from 33% of the total in the control trial to 26% in the NA trial, suggesting increased IMTG oxidation in the NA trial. Mean HSL activity was 2.25 + 0.15 mmol·kg dry mass−1·min−1at rest and increased ( P < 0.05) to 2.94 ± 0.20 mmol·kg dry mass−1·min−1at 5 min in control. Contrary to the hypothesis, mean HSL was not activated to a greater extent in the NA trial during exercise (2.20 + 0.28 at rest to 2.88 + 0.21 mmol·kg dry mass−1·min−1at 5 min). No further HSL increases were observed at 20 or 40 min in both trials. There was variability in the response to NA ingestion, as some subjects experienced a large increase in RER and decrease in fat oxidation, whereas other subjects experienced no shift in RER and maintained fat oxidation despite the reduced FFA availability in the NA trial. However, even in these subjects, HSL activity was not further increased during the NA trial. In conclusion, reduced plasma FFA availability accompanied by increased epinephrine concentration did not further activate HSL beyond exercise alone.
On the mapping xy → (xy) n in anassociative ring
Authors: Beslin Scott J. , Iskander Awad
Published: June 2004

We consider the following condition (*) on an associative ring
R : (*). There exists a function f from R into R such that f is a group homomorphism of (R, +), f is
injective on R2, and f(xy) = (xy) n(x,y) for some
positive integer n(x, y) > 1. Commutativity and structure are
established for Artinian rings R satisfying (*), and a
counterexample is given for non‐Artinian rings. The results
generalize commutativity theorems found elsewhere. The case n(x, y) = 2 is examined in detail.