bluuebunny/crossref_metadata_2025 huggingface dataset:
Movement of yeast 1,3‐β‐glucan synthase is essential for uniform cell wall synthesis
Authors: Utsugi Takahiko , Minemura Masayo , Hirata Aiko , Abe Mitsuhiro , Watanabe Daisuke , Ohya Yoshikazu
Published: March 2003

Background:  The cell wall has an important role in maintaining cell shape. In the budding yeast Saccharomyces cerevisiae, the major filamentous component of the cell wall responsible for its rigidity is 1,3‐β‐glucan and is synthesized by 1,3‐β‐glucan synthase (GS), localized on the plasma membrane.

Results:  Observations of green fluorescent protein (GFP)‐conjugated Fks1p, a catalytic subunit of GS, revealed that it is co‐localized with cortical actin patches and moves on the cell surface at the sites of cell wall remodelling. Mutants with impaired actin patch movement show immobility of Fks1p‐GFP spots, indicating that actin patch motility is required for the movement of Fks1p. Cells with immobilized Fks1p exhibit defective cell wall structure and function. The cell wall thickness of the mutants becomes irregular, eventually leading to cell lysis.

Conclusion:  We propose that GS movement is necessary for proper cell wall remodelling.
Hyperploidy induced by drugs that inhibit formation of microtubule promotes chromosome instability
Authors: Nitta Masayuki , Tsuiki Hiromasa , Arima Yoshimi , Harada Kei , Nishizaki Takahumi , Sasaki Kousuke , Mimori Tatsuyuki , Ushio Yukitaka , Saya Hideyuki
Published: March 2003

Background: Antimicrotubule drugs (AMDs), such as taxol and vincristine, are the most important addition to the chemotherapeutic armamentarium against human cancers. It has been shown that prolonged AMD treatment induces hyperploidy in G1‐checkpoint‐defective cancer cells and that these hyperploid cells subsequently undergo apoptosis. However, a fraction of these hyperploid cells are able to survive the prolonged mitotic stress and resume cell‐cycle progression.

Results: We established hyperploid clones that escaped from cell death after AMD treatment from two glioma cell lines, U251MG and U87MG. Subtractive comparative genomic hybridization (CGH) analysis revealed that clones derived from U87MG mainly had chromosome number changes, but that those from U251MG showed both numerical and structural chromosomal changes. Furthermore, numerous aberrations identified in U251MG clones were remarkably chromosome‐specific, which may have been due to clonal selection for cells that have an advantage in growth and/or survival. All clones derived from both cell lines had abnormalities in chromosome segregation, and karyotypes of clones were more heterogeneous than those of parental cells, suggesting that cells having a higher chromosome number are subject to asymmetric chromosome segregation, resulting in a heterogeneous karyotype. All clones derived from U87MG and U251MG increased both centric and acentromeric micronuclei, suggesting the presence of chromosome structural abnormality.

Conclusions: AMD treatment induces hyperploid formation and chromosome instability in checkpoint‐deficient cancer cells.
Phosphatidylinositol 3‐phosphate 5‐kinase is required for the cellular response to nutritional starvation and mating pheromone signals in Schizosaccharomyces pombe
Authors: Morishita Masayo , Morimoto Fusako , Kitamura Kenji , Koga Takako , Fukui Yasuhisa , Maekawa Hiromi , Yamashita Ichiro , Shimoda Chikashi
Published: March 2003

Background: Phosphatidylinositol (3,5) bisphosphate, which is converted from phosphatidylinositol 3‐phosphate by phosphatidylinositol 3‐phosphate 5‐kinase, is implicated in vacuolar functions and the sorting of cell surface proteins within endosomes in the endocytic pathway of budding yeast. A homologous protein, SpFab1p, has been found in the fission yeast Schizosaccharomyces pombe, but its role is not known.

Results: Here we report that SpFab1p is encoded by ste12+ known as a fertility gene in S. pombe. The ste12 mutant grew normally under stress‐free conditions, but was highly vacuolated and swelled at high temperatures and under starvation conditions. In nitrogen‐free medium, ste12 cells were arrested in G1 phase, but partially defective in the expression of genes responsible for mating and meiosis. The ste12 mutant was defective both in the production of, and in the response to, mating pheromones. The amount of the pheromone receptor protein Map3p, was substantially decreased in ste12 cells. Map3p was transported to the cell surface, then internalized and eventually transported to the vacuolar lumen, even in the ste12 mutant.

Conclusion: The results indicate that phosphatidylinositol(3,5)bisphosphate is essential for cellular responses to various stresses and for the mating pheromone signalling under starvation conditions.
Platelet serotonin transporter density and related parameters in endurance‐trained and sedentary male subjects
Authors: STRACHAN  , MAUGHAN
Published: March 2003

A number of peripheral indices of serotonergic function were examined in endurance‐trained (ET) and sedentary males using the blood platelet as a model of the serotonergic neurone. The aim of the study was to investigate possible involvement and adaptation of the central serotonergic system in exercise‐induced fatigue. The [3H] paroxetine‐defined density of platelet serotonin transporters, platelet serotonin content and the plasma concentration of amino acids were determined in 10 ET and eight sedentary males. The mean (standard deviation) density of the serotonin transporter in the platelet membranes of the ET subjects was greater [1237 (182) fmol mg protein−1] than that of the sedentary subjects [910 (119) fmol mg protein−1; P = 0.013]. No difference (P = 0.51) could be seen between the median (range) platelet serotonin content of the ET subjects [0.98 (0.37–3.04) nmol platelet−10] and that of the sedentary subjects [0.82 (0.18–1.49) nmol platelet−10]. The platelet poor plasma concentrations of tryptophan and tyrosine were lower in the ET subjects (P = 0.028 and 0.015, respectively). The present study suggests that the platelet membrane of the ET subjects has a greater density of the serotonin transporter and that this is inversely related to the circulating concentration of the serotonin precursor, tryptophan. It remains to be resolved whether the increase in serotonin transporter density in the platelet membrane of ET subjects is reflected centrally and whether the ET platelet population may be sufficiently different from that of sedentary individuals to alter serotonin transporter density.
Decreased pulmonary vascular resistance during nasal breathing: modulation by endogenous nitric oxide from the paranasal sinuses
Authors: SETTERGREN G. , ANGDIN M. , ASTUDILLO R. , GELINDER S. , LISKA J. , LUNDBERG J.O.N. , WEITZBERG E.
Published: March 2003

Nitric oxide is present in high concentration in the human nasal airways. During inspiration through the nose a bolus is transported to the lungs. In a randomized cross‐over study the effect of two different patterns of breathing, nasal breathing and mouth breathing, was evaluated in 10 patients (mean age 65 years), breathing room air the morning of the first post‐operative day after open heart surgery. Nasal breathing is defined as inspiration through the nose and expiration through the mouth, whilst mouth breathing is the converse of this: inspiration through the mouth and expiration through the nose. Pressure in the pulmonary artery and left atrium or pulmonary artery wedge was measured together with thermodilution cardiac output and arterial and mixed venous oxygenation and acid‐base parameters. Pulmonary vascular resistance index (PVRI), venous admixture and alveolar‐arterial gradient were calculated. Nasal breathing resulted in a lower PVRI, 256 dyn s cm−5 cm−2 vs. 287 (P < 0.01). The oxygen and carbon dioxide tension and pH of arterial and mixed venous blood, venous admixture and the alveolar‐arterial gradient remained unchanged. The decreased level of PVRI during nasal breathing compared to that during mouth breathing supports the notion, that endogenous nitric oxide acts as an airborne messenger to modulate the pulmonary vascular tone during normal breathing.
Influence of arterial baroreceptors and intracerebroventricular guanabenz on synchronized renal nerve activity
Authors: GRISK O. , DIBONA G. F.
Published: March 2003

The contributions of changes in the number of active fibres and the peak interval of synchronized neural discharges to arterial baroreflex regulated alterations in renal sympathetic nerve activity were examined in intact conscious rats. Stimulation of central nervous system α2adrenoreceptors with intracerebroventricular guanabenz (10, 20, 40 μg) was used to alter renal sympathetic nerve activity by a non‐reflex mechanism in both intact and sinoaortic denervated (SAD) rats. Synchronized renal sympathetic nerve discharge was analysed with the sympathetic peak detection algorithm. When arterial pressure was increased from 50 mmHg to 150 mmHg in intact rats, the peak height (number of simultaneously active fibres) of synchronized discharges decreased in a sigmoidal fashion while the peak interval remained unchanged. Guanabenz produced a dose dependent inhibition of renal sympathetic nerve activity due to both a decrease in peak height and an increase in peak interval of synchronized discharges in both intact and SAD rats. Arterial baroreflex mediated changes in renal sympathetic nerve activity are due to changes in the number of simultaneously active nerve fibres. Central nervous system α2adrenoreceptor stimulation decreases renal sympathetic nerve activity by decreasing the number of active fibres and increasing the peak interval, acting on additional neural pathways not involved in buffering acute arterial pressure changes.
PKC‐dependent signalling mechanisms in differentiated smooth muscle
Authors: MORGAN  , LEINWEBER
Published: March 2003

Protein kinase C (PKC) is now known to play an important physiological role in essentially all cell types. This review will focus on what is known about the kinase in contractile differentiated smooth muscle. Current knowledge on the molecular structure of PKC isoforms will be discussed as they relate to mechanisms of translocation and targeting of the kinase within smooth muscle cells. Studies performed on PKC‐dependent signalling pathways in differentiated smooth muscle cells will be discussed with emphasis on studies from our laboratory, especially discussing thin filament linked pathways. Thick filament linked PKC‐dependent pathways will be described in more detail elsewhere in this monograph.
Maternal nursing behaviour and the delivery of milk to the neonatal spontaneously hypertensive rat
Authors: GOULDSBOROUGH  , BLACK  , JOHNSON  , ASHTON
Published: March 2003

Fostering spontaneously hypertensive rat (SHR) pups to Wistar–Kyoto (WKY) dams permanently lowers their adult blood pressure. SHR dams show increased nursing behaviour and the SHR pup displays an exaggerated pressor response to milk ingestion. We have therefore measured pup feeding rates and dam milk secretion rates in SHR and WKY dams nursing natural and foster litters. Maternal behaviour displayed by SHR and WKY dams nursing natural or foster litters and the milk delivery rate to non‐fasted pups were measured over postnatal days 1–21. Total milk yield by SHR and WKY dams at postnatal day 6 was measured by comparing the relative weights of milk filled and empty mammary tissue. Fostering SHR pups to WKY dams significantly lowered their mean arterial blood pressure compared with naturally reared SHR pups. SHR dams nursing their natural litters spent more time nursing and less time away from their litters than WKY dams. This difference in behaviour was reduced when dams nursed pups of the opposite strain. SHR dams delivered less milk compared with WKY dams, regardless of pup strain. Total milk yield by SHR dams was significantly lower than that of WKY dams at postnatal day 6, despite comparable mammary tissue mass, suggesting that milk intake by the SHR pup is limited by milk availability, rather than an attenuated maternal response to pup suckling stimuli. The antihypertensive effect of fostering SHR pups to WKY dams may therefore reflect an increase in milk intake during a critical period of growth and development.
Effects of bedrest on deltoideus muscle morphology and enzymes
Authors: DESPLANCHES  , HOPPELER  , MAYET  , DENIS  , CLAASSEN  , FERRETTI
Published: March 2003

To examine the effects of unweighting on the structural and metabolic adaptations of a non‐postural muscle, deltoideus muscle biopsies were taken in seven male healthy subjects, before and after a 37 day bedrest. Myofibrillar ATPase histochemistry demonstrated no change in fibre type distributions (I, IIA, IIB), in fibre cross‐sectional areas nor in capillary supply. No difference was noted in enzyme activities of oxidative metabolism (citrate synthase, 3‐hydroxy‐acyl‐CoA dehydrogenase), and glycolysis (hexokinase, lactate dehydrogenase). Electron microscopy showed a decrease in the volume density of lipids but no change in mitochondrial volume density and distribution. The results indicate that bedrest induces no major morphological and biochemical changes in deltoideus muscle, contrary to what was previously reported in vastus lateralis muscle. This lack of changes is probably related to an unaltered deltoideus muscle use.
Near‐infrared spectrophotometry determined brain oxygenation during fainting
Authors: Madsen  , Pott  , Olsen  , Nielsen  , Burcev  , Secher
Published: March 2003

During orthostatic hypotension we evaluated whether presyncopal symptoms relate to a reduced brain oxygenation. Nine subjects performed 50° head‐up tilt for 1 h and eight subjects were followed during 2 h of supine rest and during 1 h of 10° head‐down tilt. Cerebral perfusion was assessed by transcranial Doppler determined middle cerebral artery blood velocity (MCA vmean), while brain blood oxygenation was assessed by near‐infrared spectrophotometry determined concentration changes for oxygenated (ΔHbO2) and deoxygenated haemoglobin and brain cell oxygenation by the oxidized cytochrome c concentration (ΔCytO2). During head‐up tilt, six volunteers developed presyncopal symptoms and mean arterial pressure (88 (78–103) to 68 (57–79) mmHg; median and range), heart rate (96 (72–111) to 65 (50–107) beats min−1), MCA vmean (59 (51–82) to 41 (29–56) cm s−1), ΔHbO2 (by −5.3 (−3.0 to −14.8) μmol l−1) and ΔCytO2 were reduced (by −0.2 (−0.1 to −0.4) μmol l−1; P < 0.05). During tilt down the cardiovascular variables recovered immediately and ΔHbO2 increased to 2.2 (−0.9–12.0) mmol L−1 above the resting value and also ΔCytO2 recovered. In the nonsyncopal head‐up tilted subjects as in the controls, blood pressure, heart rate, MCA vmean and brain oxygenation indices remained stable. The results suggest that during orthostasis, presyncopal symptoms relate not only to cerebral hypoperfusion but also to reduced brain oxygenation.
Interaction between the renin–angiotensin system and insulin‐like growth factor I in aorto‐caval fistula‐induced cardiac hypertrophy in rats
Authors: WÅHLANDER  , WICKMAN  , ISGAARD  , FRIBERG
Published: March 2003

The effects of angiotensin converting enzyme inhibition and angiotensin II receptor blockade on the development of cardiac hypertrophy and myocardial insulin‐like growth factor I (IGF‐I) in volume overload were studied in male Wistar rats with aorto‐caval fistulas (ACF). Rats were treated with ramipril (RAM, 3 mg kg–1 day–1) for 4–20 days or losartan (LOS, 10 mg kg–1 day–1) for 2–7 days. Myocardial IGF‐I and IGF‐I receptor (IGF‐I‐R) mRNA were determined by solution hybridization. ACF caused hypertrophy of left (LV) and right ventricles (RV). Hypertrophy appeared on day 2 and reached maximal values of +60% in LV and +75% in RV at day 12. Systolic blood pressure was initially reduced 15% but recovered by day 12. RAM abolished the recovery of blood pressure. Furthermore, RAM attenuated RV hypertrophy by 17% on day 7 and on day 20, RV weights were close to values found in controls. Beginning on day 9, RAM reduced LV weight back to control levels in parallel to blood pressure. In contrast, LOS affected neither RV nor LV hypertrophy. RV IGF‐I mRNA increased 60–100% on day 7 alone in RV in ACF. RAM potentiated the increase in RV IGF‐I to +400% and induced an increase in RV IGF‐I‐R mRNA on day 7 (+90%) in ACF. LOS did not affect RV IGF‐I. Development of cardiac hypertrophy in ACF seemed independent of angiotensin II. RV hypertrophy was associated with activation of IGF‐I independent of the renin–angiotensin system. IGF‐I was further potentiated when development of hypertrophy was attenuated, possibly indicative of a greater urge for compensational growth in a relatively thinner and more volume‐distended chamber.
Regulation of GLUT4 protein expression and glycogen storage after prolonged exercise
Authors: KUO  , BROWNING  , IVY
Published: March 2003

The purpose of this study was to determine the time course of GLUT4 protein accumulation following an exercise–carbohydrate supplementation regimen, and to evaluate the effect of this regimen on GLUT4 mRNA regulation. Rats were exercised by swimming and intubated with 1 mL of a 50% glucose solution immediately post‐exercise. Exercise significantly reduced muscle glycogen by 50%. By 1.5 h of recovery, muscle glycogen was normalized, but continued to increase above the control level during the next 16 h. A faster and larger repletion of glycogen occurred in the fast‐twitch red compared with the fast‐twitch white muscle during the 16 h of recovery. GLUT4 protein concentration in fast‐twitch red muscle was significantly increased above control by 1.5 h of recovery, and progressively increased throughout the recovery period. Fast‐twitch white muscle demonstrated a similar trend, but the increase in GLUT4 protein did not reach significance until 5 h of recovery. Fast‐twitch red muscle GLUT4 mRNA was increased by 53% above control immediately post‐exercise, but returned to the control level by 1.5 h of recovery. GLUT4 mRNA associated with polysomes, however, increased significantly during this time and remained elevated for a minimum of 5 h. The results suggest that the increased GLUT4 protein expression following a regimen of exercise–carbohydrate supplementation occurs sufficiently fast to contribute to the resynthesis of muscle glycogen, and is controlled by both pre‐translational and translational mechanisms.
Sustained vessel dilation induced by increased pulsatile perfusion of porcine carotid arteries in vitro
Authors: Recchia  , Byrne  , Kass
Published: March 2003

Arterial pulse pressure (PP) increases with exertional stress and ageing, and can modify vessel diameter in smaller vessels. To test if PP must exceed a certain range to influence vessel diameter, and determine if such effects are endothelium‐dependent or intrinsic to vascular viscoelasticity, eight fresh excised porcine carotid artery segments were perfused with modified Krebs–Henseleit by a servo‐controlled system generating physiological arterial pressure waveforms. In a separate group of vessels (n = 10), the endothelium was mechanically removed. Vessel external diameter was measured by video edge‐detection. Vessels partially preconstricted with noradrenaline were perfused at 9 mL min–1 mean flow, at mean pressure of 90 or 120 mmHg, and zero PP. PP alone was then increased to 40, 70, or 120 mmHg at 1 Hz cycling rate for 5 min, then returned to zero and vessel diameter measured immediately thereafter. The protocol was repeated after 10–20 min stabilization. Mean vessel diameter rose proportionally with PP only once PP exceeded 40 mmHg, with maximal increases of 6–9% at a PP of 120 mmHg. Similar responses were obtained in vessels with and without a functional endothelium, at both mean pressures. Thus, when exposed to higher than normal resting PP, conduit arteries dilate owing to the stress‐relaxation response of their viscoelastic wall. This mechanism of PP‐mediated vascular dilatation may contribute to enhanced organ perfusion when small resistance arteries are already dilated.
Decrease in sodium–calcium exchange and calcium currents in diabetic rat ventricular myocytes
Authors: Chattou  , Diacono  , Feuvray
Published: March 2003

This study was designed in order to gain insight into possible changes in the inward sodium–calcium exchange current (INa–Ca) and theL‐type calcium current (ICa), in ventricular myocytes isolated from streptozotocin‐induced diabetic rats. Recordings were made using the nystatin‐perforated patch technique which minimizes interference with the normal intracellular Ca2+buffering mechanisms. The averagedINa–Cacurrent density elicited by Ca2+current was smaller in diabetic than in normal myocytes at all potentials tested.INa–Caactivated by rapid application of caffeine was significantly reduced and the decay phase was prolonged. The density ofICawas also significantly reduced by diabetes in the range of test potentials between –10 and +50 mV. In addition, the fast time constant ofICainactivation, which represents mainly the sarcoplasmic reticulum (SR) Ca2+release‐induced inactivation, was significantly higher in diabetic than in normal myocytes. The decrease inICa, which is the main source of trigger Ca2+for SR Ca2+release, may explain the significantly lowered peak systolic [Ca2+]ipreviously shown in diabetic myocytes. As activation ofICais essential for subsequent stimulation ofINa–Ca, reducedICamay contribute to decreasing activation of the Na+–Ca2+exchanger.
Change point in V˙CO2 during incremental exercise test: a new method for assessment of human exercise tolerance
Authors: Zoladz  , Szkutnik  , Majerczak  , Duda
Published: March 2003

The main purpose of this study was to present a new method to determine the level of power output (PO) at which V˙CO2 during incremental exercise test (IT) begins to rise non‐linearly in relation to power output (PO) – the change point in V˙CO2 (CP‐V˙CO2). Twenty‐two healthy non‐smoking men (mean ± SD: age 22.0 ± 0.9 years; body mass 74.5 ± 7.5 kg; height 181 ± 7 cm; V˙O2max 3.753 ± 0.335 l min–1) performed an IT on a cycloergometer. The IT started at a PO of 30 W, followed by gradual increases of 30 W every 3 min. Antecubital venous blood samples were taken at the end of each step and analysed for plasma lactate concentration [La]pl, blood PO2, PCO2 [HCO3–]b and [H+]b. In the detection of the change‐point V˙CO2 (CP‐V˙CO2), a two‐phase model was assumed for the ‘third‐minute‐data’ of each step of the test. In the first phase, a linear relationship between V˙CO2 and PO was assumed, whereas in the second, an additional increase in V˙CO2 was allowed, above the values expected from the linear model. The PO at which the first phase ends is called the change point in V˙CO2. The identification of the model consists of two steps: testing for the existence of the change point, and estimating its location. Both procedures are based on suitably normalized recursive residuals (see
Zoladz et al. 1998a
. Eur J Appl Physiol78, 369–377). In the case of each of our subjects it was possible to detect the CP‐V˙CO2 and the CP‐V˙O2 as described in our model. The PO at the CP‐V˙CO2 amounted to 134 ± 42 W. The CP‐ V˙O2 was detected at 136 ± 32 W, whereas the PO at the LT amounted to 128 ± 30 W and corresponded to 49 ± 11, 49 ± 8 and 47 ± 8.6% V˙O2max, respectively, for the CP‐V˙CO2, CP‐V˙O2 and the LT. The [La]pl at the CP‐V˙CO2 (2.65 ± 0.76 mmol L–1), at the CP‐V˙O2 (2.53 ± 0.56 mmol L–1) and at the LT (2.25 ± 0.49 mmol L–1) were already significantly higher (P < 0.01, Students t‐test) than the value reached at rest (1.86 ± 0.43 mmol L–1). Our study illustrates that the CP‐V˙CO2 and the CP‐V˙O2 occur at a very similar power output as the LT. We therefore postulate that the CP‐V˙CO2 and the CP‐V˙O2 be applied as an additional criterion to assess human exercise tolerance.
Nitric oxide and preglomerular vascular lesions in Lyon spontaneously hypertensive rats
Authors: Casellas  , Bouriquet  , Artuso
Published: March 2003

Accumulation of Sudan black‐stainable (SB+) lipids is a hallmark of the focal inflammato‐proliferative lesions that develop along preglomerular vessels in N G‐nitro‐
L‐arginine methyl ester (
L‐NAME) and angiotensin II hypertensive rats. We extended our findings to genetically hypertensive Lyon (LH) rats aged 14 and 30 weeks and to age‐matched normotensive (LN) rats. Vessels were isolated by HCl maceration. Despite high systolic blood pressure (SBP), hypercholesterolaemia, albuminuria and increased interlobular and afferent arteriolar media thickness, SB+ lesions were rarely found in LH rats, regardless of age. To probe nitric oxide as a potential source of vascular protection, 14‐week‐old LN and LH rats received
L‐NAME for 10 days (20 mg kg–1 day–1, per os), which increased SBP to 174 ± 5 and to >200 mmHg, respectively. It induced formation of focal SB+ lesions less frequently in LN than LH rats, in which they affected 39 ± 7, 44 ± 5 and 15 ± 5% of arcuate arterial branches, interlobular arteries and afferent arterioles, respectively. Immunoreactive endothelin‐1 was found to accumulate at the level of SB+ lesions. Co‐administered with
L‐NAME, hydralazine (15 mg kg–1 day–1, per os) limited SBP rise to ≈10 mmHg in both LN and LH rats. As a result, SB+ lesions were rare in LN rats, but were frequent in LH rats. In conclusion, preglomerular SB+ lesions are spontaneously lacking in LH rats. Endogenous nitric oxide production provides protection against vascular barotrauma. Endothelin‐1 likely plays an autocrine/paracrine role in vascular lesion formation.
Chronic increases in transmural pressure reduce NO‐mediated dilations in isolated resistance arteries of the hamster
Authors: Bolz  , Pieperhoff  , De Wit  , Pohl
Published: March 2003

It is unclear whether the impairment of NO‐mediated dilation in hypertension is the cause or the consequence of high blood pressure. We therefore studied in isolated resistance arteries whether elevated transmural pressure affects NO‐mediated dilation. Arteries (n=5–7) were perfused at hydrostatic pressures of either 45, 120 or 160 mmHg for 48 h. Subsequently, diameter and calcium responses (fura 2) were studied at a transmural pressure of 45 mmHg. Pre‐exposure to 120 and 160 mmHg reduced resting diameters and minimal diameters after stimulation with noradrenaline and significantly increased corresponding intracellular free calcium levels in vascular smooth muscle. Moreover, the NO‐mediated dilation in response to acetylcholine was significantly reduced although the increase in endothelial calcium was not altered. Dilations induced by the NO donor SNP were not affected. It is concluded that chronically elevated pressure per se impairs endothelial NO production by a mechanism distal to receptor‐dependent calcium increases.
Advanced glycosylation end‐products and NO‐dependent vasodilation in renal afferent arterioles from diabetic rats
Authors: Moore  , Thorup  , Ellinger  , Paccione  , Casellas  , Kaskel
Published: March 2003

Systemic pressor responses to acetylcholine (ACh) are reduced in DM, an effect thought to be related to quenching of nitric oxide (NO) by advanced glycosylation end‐products (AGE). We studied the effects of AGE in juxtamedullary (JM) afferent arterioles (AA) from rats with 40–50 days diabetes mellitus (DM) induced via streptozotocin. JM AA were perfused in vitro with solutions containing fresh RBCs suspended in either 6% bovine albumin or 6% AGE‐albumin in euglycaemic Krebs–Ringer. Autoregulatory responses were evident in the DM vessels: AA constricted 31 ± 2% (n=9) when perfusion pressure (PP) was raised from 60 to 140 mmHg. ACh (10 μM) caused a 43 ± 15% dilation and Ca2+‐channel blockade elicited a 95 ± 14% dilation at 100 mmHg PP, indicating substantial basal vascular tone in DM AA.
L‐NAME (0.1 m
M) constricted DM AA by 21 ± 2% (n=9) at 100 mmHg PP, indicating significant basal NO production in DM vessels. Segments of renal resistance arteries from DM rats perfused in vitro responded to muscarinic stimulation and elevated glucose levels with significant increments in NO production, as measured with an NO‐sensitive electrode. This observation shows that the renal endothelial NO system is intact in DM. While AGE in the perfusate dilated control AA, they had no effect on DM AA at all PP levels, although they blunted ACh‐induced dilation. Hence, although AGE do appear to have vasoactive properties in the absence of hyperglycaemia, the results of this study are inconsistent with substantial NO quenching by AGE.
Biological effects of arginine metabolites
Authors: Blantz  , Satriano  , Gabbai  , Kelly
Published: March 2003

Arginine and its metabolites exert physiological effects on the vasculature and on the kidney and also provide important influences on the regulation of cell proliferation. We summarize the known information regarding two major metabolites of arginine: (a) nitric oxide (NO) and (b) agmatine, decarboxylated arginine. Both agents appear to interact in producing vasodilation and increases in glomerular filtration rate (GFR) in the kidney. There is evidence for inter‐regulation of arginine pathways in the sense that agmatine is capable of inhibiting inducible nitric oxide synthase (iNOS), the inflammatory NOS isoform. Both NO and agmatine influence cell proliferation via effects on polyamine synthesis. In addition, both NO and agmatine exert inhibitory effects on ornithine decarboxylase (ODC) and the putrescine transporter by significantly different mechanisms. Therefore, arginine and arginine metabolites exert both vascular regulatory functions and impact on the regulation of cell proliferation. Significant inter‐regulation among arginine pathways occurs within the three metabolic major pathways within the cell: (1) nitric oxide synthase (2) arginase and ornithine decarboxylase, and (3) arginine decarboxylase.
The autoinhibitory control element and calmodulin conspire to provide physiological modulation of endothelial and neuronal nitric oxide synthase activity
Authors: Lane  , Gross
Published: March 2003

NO production by the endothelial and neuronal isoforms of nitric oxide synthase (cNOS) is regulated on a moment‐to‐moment basis by calmodulin binding, triggered by transient elevations in intracellular‐free calcium levels. Nonetheless, additional modes of cNOS regulation are implicit in the discoveries of stimuli that elicit a sustained increase in cNOS activity despite undetectable or transient increases in intracellular Ca2+ in endothelial cells; such stimuli include shear‐stress, oestrogen, insulin or insulin‐like growth factor treatment of endothelial cells. Recently, we identified a peptide insertion within the FMN‐binding domain of mammalian NOSs that is unique to calcium‐dependent isoforms, and not shared with inducible NOS or ancestral flavoproteins. Evidence suggests that this insertion serves as a fundamental control element, analogous to intrinsic autoinhibitory peptides that have been demonstrated to regulate activity of other calmodulin‐dependent enzymes. Thus, the peptide insertion of cNOSs appears to function as structural element that is displaced upon calmodulin binding, resulting in dysinhibition of NO synthesis. Once displaced, the peptide may also be subject to transient chemical modifications and protein–protein interactions that modulate autoinhibitory function. Herein we summarize our present knowledge and speculate on mechanisms by which calmodulin and the autoinhibitory peptide conspire to regulate cNOS activity.
Renal sodium/calcium exchange; a vasodilator that is defective in salt‐sensitive hypertension
Authors: Bell  , Mashburn  , Unlap
Published: March 2003

The Na+ : Ca2+ exchanger is an important plasma membrane ion transport pathway that plays a major role in controlling [Ca2+]i. In smooth muscle cells, it may function as a Ca2+ extrusion pathway and may help lower [Ca2+]i in response to vasoconstrictor‐induced increases in [Ca2+]i. It may also extrude [Ca2+]i and lead to vasodilation in response to vasodilators. Our recent studies have been performed to determine the existence and regulation of the Na+ : Ca2+ exchanger in renal contractile cells which include afferent and efferent arterioles and mesangial cells. Exchanger activity is present in all three of these contractile elements but is higher in afferent arterioles vs. efferent arterioles. We have also examined the role of altered regulation of the exchanger in the SHR and in salt‐sensitive hypertension. With the establishment of high blood pressure, Na+ : Ca2+ exchanger activity is reduced in afferent but not in efferent arterioles in both models of hypertension. Other works in cultured mesangial cells and freshly dissected afferent arterioles, have shown that protein kinase C (PKC) up‐regulates the Na+ : Ca2+ exchanger from Dahl/Rapp salt‐resistant rats while it fails to do so in arterioles and mesangial cells from salt‐sensitive rats. This defect in PKC regulation of Na+ : Ca2+ exchange is the result of a loss of PKC‐mediated translocation of the exchanger to the plasma membrane in S mesangial cells. Thus, a defect in the PKC‐Na+ : Ca2+ exchanger‐translocation pathway may cause dysregulation of [Ca2+]i and help explain the dramatic decrease in GFR that occurs in this model of hypertension.
No apparent effect of nitric oxide on the local matching of pulmonary perfusion and ventilation in awake sheep
Authors: Melsom  , Flatebø  , Nicolaysen
Published: March 2003

The respiratory tissue in the lung receives nitric oxide (NO) from two sources; NO produced in upper airways, and NO produced in lung parenchyma. It has been hypothesized that optimal local matching of ventilation and perfusion (which is necessary for effective gas exchange) is ensured because well‐ventilated lung tissue has a higher concentration of NO and thereby higher blood flow owing to the vasodilatory effect of NO. To test this hypothesis, we simultaneously measured the distributions of local (regions of ≈1.5 cm3) blood flow (radioactive microspheres) and local ventilation (fluorescent aerosol) in five tracheostomized, awake and standing sheep. Tracers for perfusion and ventilation were administered (1) at baseline, (2) during endogenous NO production blockage (
L‐NAME 25 mg kg–1) and administration of NO free air, and (3) when the sheep received exogenous NO (≈30 p.p.m.), but having its endogenous NO production blocked. The intrapulmonary distribution of ventilation was similar in all three situations. Within horizontal levels of the lung, distribution of perfusion was not affected by variable access to NO, but along the gravitational axis perfusion was more evenly distributed when the sheep had no access to NO. Exogenous NO tended to restore the baseline vertical profile. These changes in vertical distribution of perfusion can be explained by the effect of variable NO concentrations on pulmonary arterial pressure and cardiac output. Variable access to NO had no effect on arterial blood gases. We conclude that NO is important for the vertical distribution of pulmonary perfusion, but has no apparent effect on the local matching of ventilation and perfusion within horizontal layers of the lung.
Muscle oxygen uptake in humans at onset of and during intense exercise
Authors: Bangsbo J.
Published: March 2003

This review presents data on human muscle oxygen consumption in the initial phase of exercise as well as on muscle maximal oxygen uptake. It also discusses mechanistic limiting factors related to oxygen utilization at the onset of exercise and of maximal aerobic power of skeletal muscle. Direct measurements of oxygen utilization of a well‐defined muscle show that contracting muscles utilize oxygen within a few seconds of exercise onset and that it takes some 45 s before oxygen extraction is maximal. The delayed oxygen utilization in the initial phase of intense exercise does not appear to be caused by insufficient oxygen availability. But it may rather be the result of a non‐optimal distribution of blood flow in the exercising muscles and a limitation in the rate of oxygen extraction by the contracting muscle cells. The latter limitation does not appear to be caused by an insufficient activation of the enzyme pyruvate dehydrogenase. The maximal oxygen uptake of skeletal muscle is around 300–400 mL min–1 kg–1. This uptake rate corresponds to a TCA cycle rate of 4–5 mmol min–1 kg–1, which is of the same magnitude as the activity of oxyglutarate dehydrogenase and pyruvate dehydrogenase, suggesting that these enzymes may be rate limiting for oxygen uptake when an isolated muscle is exercising.
Large arterioles in the control of blood flow: role of endothelium‐dependent dilation
Authors: Pohl U. , De Wit C. , Gloe T.
Published: March 2003

Although it is generally assumed that small arterioles form the major site of vascular resistance, microcirculatory studies revealed that 40–55% of the total network resistance can reside in large arterioles and small arteries. Thus, the mechanisms that control smooth muscle tone in these vessels have a major impact on the overall conductance of the vascular network. These control mechanisms are different from those in small arterioles: Aside from an apparently reduced sensitivity to metabolites, the large resistance vessels are normally too far away from the capillary areas which they feed to be reached by diffusing metabolites from dependent cells within a reasonable period of time. Rather, recent intravital microscopic studies suggest that large resistance vessels are under tight control of endothelial factors such as nitric oxide and endothelium‐derived hyperpolarising factor (EDHF). Nitric oxide opposes myogenic constrictions of large arterioles that potentially would impair tissue perfusion and oxygenation. Moreover, nitric oxide and EDHF play an important role in the co‐ordination of large and small resistance vessel behaviour that is pivotal for the adaptation of blood flow to altered tissue oxygen demands.
Deciphering the mysteries of myoglobin in striated muscle
Authors: Conley K.E. , Ordway G.A. , Richardson R.S.
Published: March 2003

Myoglobin (Mb) is a large protein that reversibly binds oxygen in the muscle cell and is thought to be critical for O2 supply to the mitochondria during exercise. The role of Mb in aerobic function is evaluated based on the physical properties of Mb as an O2 carrier and experimental evidence of Mb function in vivo. This role depends on the reversible binding of O2 by Mb depending on PO2, which results in: (1) storage of O2; (2) buffering of PO2 in the cell to prevent mitochondrial anoxia; and (3) parallel diffusion of O2 (so‐called, ‘facilitated diffusion’). The storage role is well established in diving mammals and buffering of cell PO2 above anoxic levels is shown here by in vivo magnetic resonance spectroscopy (MRS). However, the quantitative role of Mb in ‘facilitated’ or parallel diffusion of O2 is controversial. Evidence in support of this role is from MRS analyses, which reveal rapid Mb desaturation with exercise, and from the proportionality of Mb content of a muscle to the O2 diffusion limitation. Recent experiments with myoglobin knockout mice demonstrating high levels of aerobic function in normal and myoglobin‐free mice argue against a link between Mb and oxidative phosphorylation. Thus, the current evidence supports the role of Mb in the physical diffusion of O2; however, the unimpaired aerobic function of Mb knockout mice indicates that this role may not be critical to O2 supply in active muscle.
Sustained increase in arterial blood pressure and vascular resistance induced by infusion of arachidonic acid in rats
Authors: Kirkebø  , Haugan  , Mesteig
Published: March 2003

The haemodynamic responses to arachidonic acid (AA) have been investigated in seven groups of anaesthetized rats. Sodium arachidonate was infused intravenously for 4 or 20 min, and arterial blood pressure was recorded continuously. Cardiac output and organ blood flow were measured by microspheres. Infusion of arachidonate caused first a fast drop in arterial blood pressure, thereafter it increased steadily for 5–15 min towards a pressure about 25 mmHg above control level. The high pressure was maintained for at least 1 h. Repeated infusions of arachidonate gave similar responses. Inhibition of cyclo‐oxygenase by indomethacin prevented the initial pressure drop to arachidonate, but not the sustained increase in pressure. Arterial pressure, total vascular resistance and blood flow in the kidneys, adrenals and spleen were significantly reduced, whereas cardiac output was not changed 4 min after start infusion of arachidonate. However, average blood pressure was significantly increased 22 and 35 min after start infusion (from 103.9 ± 2.9 to 128.1 ± 6.1 and 135.8 ± 4.6 mmHg). Mean vascular resistance increased simultaneously (from 3.5 ± 0.2 to 4.7 ± 0.4 and 5.2 ± 0.4 mmHg 100 mL–1), while cardiac output, stroke volume and heart rate were maintained or slightly reduced. The renal blood flow was significantly lowered (from average 4.9 ± 0.1 to 3.3 ± 0.2 and 4.0 ± 0.2 mL min–1). Indomethacin did not prevent the changes in vascular resistance or organ blood flow recorded after 20–35 min. On the other hand, inhibition of both cyclo‐oxygenase, lipoxygenase and the cytochrome P450 pathways by eicosatetrayonic acid (ETYA) normalized all haemodynamic parameters. Likewise, the rise in pressure was prevented by 17‐octadecynoic acid (17‐ODYA), an inhibitor of the cytochrome P450 enzyme activity. Thus, arachidonate infusion caused a transient decrease, and then a sustained increase in arterial pressure and vascular resistance, and a long‐lasting reduction in renal blood flow, possibly owing to release of a cytochrome P450 dependent vasoconstrictor metabolite of AA.
Expression of the Na+/H+ exchanger isoform NHE1 in rat skeletal muscle and effect of training
Authors: Juel
Published: March 2003

The expression of the Na+/H+ exchanger isoform NHE1 was quantified in homogenates of various rat skeletal muscles by means of immunoblotting, and the effect of 3 weeks of treadmill training on NHE1 expression was determined in a red (oxidative) as well as a white (glycolytic)‐muscle preparation. The NHE1 antibodies recognized a glycosylated protein at 101–111 kDa. There was a positive correlation between the NHE1 expression in the muscle and percent type IIB fibres and percent type IID/X fibres, whereas the NHE1 expressions were negatively correlated to percent type I fibres and percent type I + IIA fibres. Thus the highest NHE1 expression was evident in the most glycolytic fibres. Treadmill training increased (P < 0.05) the NHE1 content by 29 and 36% in oxidative and glycolytic fibres, respectively, suggesting that training enhanced the NHE1 content of all muscle‐fibre types. Therefore training may improve the capacity for pH regulation in skeletal muscle.
No effect of venoconstrictive thigh cuffs on orthostatic hypotension induced by head‐down bed rest
Authors: Custaud M.‐A. , Millet C. , Frutoso J. , Maillet A. , Gauquelin G. , Gharib C. , Fortrat J.‐O.
Published: March 2003

Orthostatic intolerance (OI) is the most serious symptom of cardiovascular deconditioning induced by head‐down bed rest or weightlessness. Wearing venoconstrictive thigh cuffs is an empirical countermeasure used by Russian cosmonauts to limit the shift of fluid from the lower part of the body to the cardio‐cephalic region. Our aim was to determine whether or not thigh cuffs help to prevent orthostatic hypotension induced by head‐down bed rest. We studied the effect of thigh cuffs on eight healthy men. The cuffs were worn during the day for 7 days of head‐down bed rest. We measured: orthostatic tolerance (stand tests and lower body negative pressure tests), plasma volume (Evans blue dilution), autonomic influences (plasma noradrenaline) and baroreflex sensitivity (spontaneous baroreflex slope). Thigh cuffs limited the loss of plasma volume (thigh cuffs: −201 ± 37 mL vs. control: −345 ± 42 mL,P < 0.05), the degree of tachycardia and reduction in the spontaneous baroreflex sensitivity induced by head‐down bed rest. However, the impact of thigh cuffs was not sufficient to prevent OI (thigh cuffs: 7.0 min of standing time vs. control: 7.1 min). Decrease in absolute plasma volume and in baroreflex sensitivity are known to be important factors in the aetiology of OI induced by head‐down bed rest. However, dealing with these factors, using thigh cuffs for example, is not sufficient to prevent OI. Other factors such as venous compliance, microcirculatory changes, peripheral arterial vasoconstriction and vestibular afferents must also be considered.
Relationship between ischaemic time and ischaemia/reperfusion injury in isolated Langendorff‐perfused mouse hearts
Authors: Wang Q.‐D. , Swärdh A. , Sjöquist P.‐O.
Published: March 2003

Myocardial functional recovery and creatine kinase (CK) release following various periods of ischaemia were investigated in isolated mouse hearts. The hearts were perfused in the Langendorff mode with pyruvate‐containing Krebs–Hensleit (KH) buffer under a constant perfusion pressure of 80 mmHg, and were subjected to either continuous perfusion or to 5, 15, 20, 25, 30, 45 or 60 min of global ischaemia followed by 45 min of reperfusion. In hearts subjected to ischaemic periods of 5, 15 or 20 min, there was a transient reduction in the left ventricular (LV) dP/dt max during the early phase of reperfusion, while the recovery at the end of reperfusion reached a level similar to that in hearts subjected to continuous perfusion. In hearts subjected to longer ischaemic periods, i.e. 25, 30, 45 or 60 min, the decrease in the cardiac performance was more pronounced and persistent, with significantly lower recovery in LV dP/dt max and higher LV end diastolic pressure (LVEDP) at the end of reperfusion than in the non‐ischaemic hearts. There were no significant differences in the recoveries in coronary flow or in heart rate (HR) between groups. Similarly to the functional recovery, the release of CK showed a clear ischaemic length‐related increase. In conclusion, the Langendorff‐perfused isolated mouse heart could be a valuable model for studies of myocardial ischaemia/reperfusion injury. Future studies using gene‐targeted mice would add valuable knowledge to the understanding of myocardial ischaemia/reperfusion injury.
Insulin insensitivity and delayed transcapillary delivery of insulin in oophorectomized rats treated with testosterone
Authors: Holmäng A. , Niklasson M. , Rippe B. , Lönnroth P.
Published: March 2003

The importance of transcapillary insulin delivery as a regulated step was explored in an insulin resistant rat model. Oophorectomized female rats were exposed to testosterone (OVX + T) for 8 weeks and examined with insulin clamps, muscle microdialysis, and analyses of insulin distribution kinetics. The results were compared with those obtained in sham‐operated control rats. After OVX + T, onset of glucose uptake in skeletal muscle was significantly (P < 0.001–0.05) delayed compared with controls as measured by the glucose infusion rate (GIR) during a euglycaemic, hyperinsulinaemic clamp (5 mU kg–1 min–1). The increase in interstitial insulin concentrations was also significantly (P < 0.05) delayed (15–20% lower) in OVX + T treated rats compared with control rats, but to such a small magnitude that this alone could not explain the late onset of the insulin effect. Skeletal muscle capillary density, examined histochemically, was diminished (P < 0.01–0.001) by 20–25% after treatment with OVX + T compared with control animals, as was the peripheral blood flow (P < 0.05) by 40–45%, measured with the microsphere technique. Insulin binding was reduced in proportion to the reduced (P < 0.01) vascular surface area by OVX + T treatment. Transcapillary transport rate of insulin, measured by comparisons of the kinetics of inulin and insulin spaces in muscle with time, tended (ns) to be lower after OVX + T compared with control rats (30–40%) as a reflection of the lower capillary surface area. The data suggest that the delayed onset of insulin action after OVX + T results from combined defects in the muscle cell at a postreceptor level and, to a lesser extent, from retarded transcapillary delivery of insulin.