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Maximal Rate (maximal + rate)
Selected AbstractsPatterns of respiration in Locusta migratoria nymphs when feedingPHYSIOLOGICAL ENTOMOLOGY, Issue 1 2000Scott M. Gouveia Summary Flow-through respirometry was used to investigate patterns of respiration of fifth-instar Locusta migratoria L. nymphs fed a chemically defined, synthetic food. Each animal was recorded for up to 2.7 h, during which they had access to food and water ad libitum, and at least one meal was taken. The start of feeding was coincident with a sudden and rapid rise in respiration. Both carbon dioxide (CO2) production and oxygen (O2) consumption rose, the traces for the two gasses showing a high degree of alignment. The end of a meal correlated with a sudden and rapid decrease in respiratory rate towards resting levels. When feeding was interrupted by an intra-meal pause, respiratory rate tended to drop marginally and then stabilize, before rising rapidly upon the resumption of feeding within the meal. Maximal rates of respiration during feeding represented a 3,4-fold increase over those at rest. Walking and climbing within the chamber were not associated with any noticeable change in respiratory rate above baseline. When locusts were quiescent between feeding episodes, respiration was steady and continuous, rather than discontinuous. Possible causes for large changes in respiration during feeding are discussed. [source] Combined Oral Contraceptives do not Influence Post-Exercise Hypotension in WomenEXPERIMENTAL PHYSIOLOGY, Issue 5 2002Karen Birch The aim of the present study was to examine the pattern of cardiovascular recovery from exercise in 15 women (age, 20.3 ± 1.4 years; body mass, 61.5 ± 4.3 kg) across two phases of oral contraceptive (OC) use: 21 days of consumption and 7 days of withdrawal. Cardiovascular recovery was measured in the supine position for 60 min following 30 min of exercise at 60% maximal rate of oxygen consumption (V,O2,max). Central and peripheral haemodynamics were assessed during consumption and withdrawal of the OC pill using occlusion plethysmography, Doppler flowmetry and echocardiography. Significant hypotension occurred following exercise (P < 0.05), returning to baseline values after 60 min. The peak hypotension occurred 5 min into recovery. Cardiac output and heart rate were elevated for 60 min following exercise (P < 0.05), whilst stroke volume remained at baseline values. Heart rate was greater throughout recovery during consumption compared to withdrawal (P < 0.05); however, although there was a trend for greater responses during consumption, phase of OC use did not affect the other central cardiovascular variables (P > 0.05). Post-exercise blood flow parameters were not significantly affected by exercise or OC phase; however, calf blood flow was greater, and resistance to flow lower during consumption (P > 0.05). The pattern of post-exercise fluctuations in cardiovascular parameters may differ from those seen in men, whilst oestrogen variation may influence research findings. [source] Kinetics of Thyroxine (T4) and Triiodothyronine (T3) Transport in the Isolated Rat HeartEXPERIMENTAL PHYSIOLOGY, Issue 1 2001Mirko A. Rosic The dynamics and kinetics of thyroid hormone transport in the isolated rat heart were examined using the modified unidirectional paired tracer dilution method. The uptake of 125I-thyroxine (125I-T4) and 125I-triiodothyronine (125I-T3) from the extracellular space into heart cells was measured relative to the extracellular space marker 3H-mannitol. The thyroid hormone maximal uptake was 54.4% for 125I-T4 and 52.15% for 125I-T3. The thyroid hormone net uptake was 25.69% for 125I-T4 and 25.49% for 125I-T3. Backflux from the intracellular space was 53.17% for 125I-T4 and 61.59% for 125I-T3. In the presence of unlabelled thyroid hormones, 125I-T4 and 125I-T3 maximal uptakes were reduced from 10.1 to 59.74% and from 34.6 to 65.3%, respectively, depending on the concentration of the unlabelled hormone, suggesting a saturable mechanism of the thyroid hormone uptake by the heart cells, with Km(T4)= 105.46 ,M and the maximal rate of 125I-thyroid hormone flux from the extracellular space to heart cells (Vmax(T4)) = 177.84 nM min,1 for 125I-T4 uptake, and Km(T3)= 80.0 ,M and Vmax(T3)= 118.5 nM min,1 for 125I-T3 uptake. [source] Impaired Detection of Ventricular Tachyarrhythmias by a Rate-Smoothing Algorithm in Dual-Chamber Implantable Defibrillators: Intradevice InteractionsJOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 4 2002MICHAEL GLIKSON M.D. Rate-Smoothing Algorithm in ICD.Introduction: Rate smoothing is an algorithm initially designed to prevent rapid changes in pacemaker rates. In this study, we sought to determine the potential of the rate-smoothing mechanism in preventing detection of ventricular tachyarrhythmias. Methods and Results: Clinical testing of rate smoothing was performed at the time of defibrillator arrhythmia induction in 16 patients with implantable defibrillators during 65 episodes of ventricular tachyarrhythmias. We also performed simulator-based testing to assess detection of ventricular tachycardia between 170 and 220 beats/min with systematic sequential change of rate-smoothing percent, AV delay, and maximal rate. During clinical testing of 54 ventricular fibrillation/polymorphic ventricular tachyarrhythmia episodes, there were no cases of nondetection and 3 episodes (5%) of minimally delayed detection. Of 10 monomorphic ventricular tachyarrhythmias, 6 had either delayed (2 cases) or absent (4 cases) detection. During simulator testing, complex interrelationships were demonstrated in AV delay, upper rate, and rate-smoothing percent in determining the severity of the effect on detection. Generally, long AV delay, higher upper rate, and smaller (more aggressive) rate smoothing were associated with increased risk of ventricular tachyarrhythmia underdetection. Importantly, use of parameters that impaired detection was always accompanied by a programmer warning message. Conclusion: Rate smoothing may result in delay or failure of ventricular tachycardia detection. It is important to consider warning messages when programming rate smoothing and to test for appropriate detection when rate smoothing is used despite warning messages. [source] Chronic Amiodarone Effects on Epicardial Conduction and Repolarization in the Isolated Porcine HeartPACING AND CLINICAL ELECTROPHYSIOLOGY, Issue 7 2000DOMINIQUE LACROIX Amiodarone is a potent antiarrhythmic agent with complex chronic effects, notably on repolarization and conduction, that are not fully understood. Its low arrhythmogenic potential has been related to a lack of increase in repolarizution dispersion. Since its effects are not documented in pigs we conducted a mapping study of activation and repolarization in isolated perfused porcine hearts. Amio20 female pigs (n = 7) received amiodarone 20 mg/kg per day over 4 weeks while Amio 5O female pigs (n = 7) received 50 mg/kg per day over 4 weeks. Concentrations of the drug encompassed values found in clinical studies. Then, activation patterns and activation-to-recovery intervals (ARI) were mapped epicardially from 128 unipolar electrograms in isolated perfused hearts in corroboration of epicardial action potential recordings. Mean ARI was longer in Amio20 experiments compared to the seven control hearts (325 ±11 ms vs 288 ± 5 m.s at 1,000 ms), whereas ARI dispersion was not different, being comprised between 7 and 11 ms and generating smooth gradients. In Amio5O experiments, mean ARI was further prolonged (390 ±10 ms at 1,500 ms) with an exaggerated reverse rate dependence concomitant with a depressant effect on the plateau of the action potential. Again, ARI dispersion did not differ from controls. Finally, the drug depressed the maximal rate of depolarization (Vmax) and slowed conduction in a rate dependent and concentration dependent fashion. In conclusion, chronic amiodarone induces Class I and Class HI antiarrhythmic effects in ventricular porcine epicardium that are concentration dependent but does not affect dispersion of repolarization. This may partly explain its low arrhythmogenic potential. [source] Growth in elevated CO2 protects photosynthesis against high-temperature damagePLANT CELL & ENVIRONMENT, Issue 6 2000Daniel R. Taub ABSTRACT We present evidence that plant growth at elevated atmospheric CO2 increases the high-temperature tolerance of photosynthesis in a wide variety of plant species under both greenhouse and field conditions. We grew plants at ambient CO2 (~ 360 ,mol mol,1) and elevated CO2 (550,1000 ,mol mol,1) in three separate growth facilities, including the Nevada Desert Free-Air Carbon Dioxide Enrichment (FACE) facility. Excised leaves from both the ambient and elevated CO2 treatments were exposed to temperatures ranging from 28 to 48 °C. In more than half the species examined (4 of 7, 3 of 5, and 3 of 5 species in the three facilities), leaves from elevated CO2 -grown plants maintained PSII efficiency (Fv/Fm) to significantly higher temperatures than ambient-grown leaves. This enhanced PSII thermotolerance was found in both woody and herbaceous species and in both monocots and dicots. Detailed experiments conducted with Cucumis sativus showed that the greater Fv/Fm in elevated versus ambient CO2 -grown leaves following heat stress was due to both a higher Fm and a lower Fo, and that Fv/Fm differences between elevated and ambient CO2 -grown leaves persisted for at least 20 h following heat shock. Cucumis sativus leaves from elevated CO2 -grown plants had a critical temperature for the rapid rise in Fo that averaged 2·9 °C higher than leaves from ambient CO2 -grown plants, and maintained a higher maximal rate of net CO2 assimilation following heat shock. Given that photosynthesis is considered to be the physiological process most sensitive to high-temperature damage and that rising atmospheric CO2 content will drive temperature increases in many already stressful environments, this CO2 -induced increase in plant high-temperature tolerance may have a substantial impact on both the productivity and distribution of many plant species in the 21st century. [source] The neurochemistry of waking and sleeping mental activity: The disinhibition-dopamine hypothesisPSYCHIATRY AND CLINICAL NEUROSCIENCES, Issue 4 2002CLAUDE GOTTESMANN Abstract This paper describes a hypothesis related to the neurochemical background of sleep-waking mental activity which, although associated with subcortical structures, is principally generated in the cerebral cortex. Acetylcholine, which mainly activates cortical neurons, is released at the maximal rate during waking and rapid eye movement (REM) sleep dreaming stage. Its importance in mental functioning is well-known. However, brainstem-generated monoamines, which mainly inhibit cortical neurons, are released during waking. Both kinds of influences contribute to the organized mentation of waking. During slow wave sleep, these two types of influence decrease in intensity but maintain a sufficiently high level to allow mental activity involving fairly abstract pseudo-thoughts, a mode of activity modelled on the diurnal pattern of which it is a poor reply. During REM sleep, the monoaminergic neurons become silent except for the dopaminergic ones. This results in a large disinhibition and the maintained dopamine influence may be involved in the familiar psychotic-like mental activity of dreaming. Indeed, in this original activation,disinhibition state, the increase of dopamine influence at the prefrontal cortex level could explain the almost total absence of negative symptoms of schizophrenia during dreaming, while an increase in the nucleus accumbens is possibly responsible for hallucinations and delusions, which are regular features of mentation during this sleep stage. [source] Phosphate metabolite concentrations and ATP hydrolysis potential in normal and ischaemic heartsTHE JOURNAL OF PHYSIOLOGY, Issue 17 2008Fan Wu To understand how cardiac ATP and CrP remain stable with changes in work rate , a phenomenon that has eluded mechanistic explanation for decades , data from 31phosphate-magnetic resonance spectroscopy (31P-MRS) are analysed to estimate cytoplasmic and mitochondrial phosphate metabolite concentrations in the normal state, during high cardiac workstates, during acute ischaemia and reactive hyperaemic recovery. Analysis is based on simulating distributed heterogeneous oxygen transport in the myocardium integrated with a detailed model of cardiac energy metabolism. The model predicts that baseline myocardial free inorganic phosphate (Pi) concentration in the canine myocyte cytoplasm , a variable not accessible to direct non-invasive measurement , is approximately 0.29 mm and increases to 2.3 mm near maximal cardiac oxygen consumption. During acute ischaemia (from ligation of the left anterior descending artery) Pi increases to approximately 3.1 mm and ATP consumption in the ischaemic tissue is reduced quickly to less than half its baseline value before the creatine phosphate (CrP) pool is 18% depleted. It is determined from these experiments that the maximal rate of oxygen consumption of the heart is an emergent property and is limited not simply by the maximal rate of ATP synthesis, but by the maximal rate at which ATP can be synthesized at a potential at which it can be utilized. The critical free energy of ATP hydrolysis for cardiac contraction that is consistent with these findings is approximately ,63.5 kJ mol,1. Based on theoretical findings, we hypothesize that inorganic phosphate is both the primary feedback signal for stimulating oxidative phosphorylation in vivo and also the most significant product of ATP hydrolysis in limiting the capacity of the heart to hydrolyse ATP in vivo. Due to the lack of precise quantification of Piin vivo, these hypotheses and associated model predictions remain to be carefully tested experimentally. [source] Action potential initiation and propagation in hippocampal mossy fibre axonsTHE JOURNAL OF PHYSIOLOGY, Issue 7 2008Christoph Schmidt-Hieber Dentate gyrus granule cells transmit action potentials (APs) along their unmyelinated mossy fibre axons to the CA3 region. Although the initiation and propagation of APs are fundamental steps during neural computation, little is known about the site of AP initiation and the speed of propagation in mossy fibre axons. To address these questions, we performed simultaneous somatic and axonal whole-cell recordings from granule cells in acute hippocampal slices of adult mice at ,23°C. Injection of short current pulses or synaptic stimulation evoked axonal and somatic APs with similar amplitudes. By contrast, the time course was significantly different, as axonal APs had a higher maximal rate of rise (464 ± 30 V s,1 in the axon versus 297 ± 12 V s,1 in the soma, mean ±s.e.m.). Furthermore, analysis of latencies between the axonal and somatic signals showed that APs were initiated in the proximal axon at ,20,30 ,m distance from the soma, and propagated orthodromically with a velocity of 0.24 m s,1. Qualitatively similar results were obtained at a recording temperature of ,34°C. Modelling of AP propagation in detailed cable models of granule cells suggested that a ,4 times higher Na+ channel density (,1000 pS ,m,2) in the axon might account for both the higher rate of rise of axonal APs and the robust AP initiation in the proximal mossy fibre axon. This may be of critical importance to separate dendritic integration of thousands of synaptic inputs from the generation and transmission of a common AP output. [source] Modulation of excitation,contraction coupling by isoproterenol in cardiomyocytes with controlled SR Ca2+ load and Ca2+ current triggerTHE JOURNAL OF PHYSIOLOGY, Issue 2 2004Kenneth S. Ginsburg Cardiac Ca2+ transients are enhanced by cAMP-dependent protein kinase (PKA). However, PKA-dependent modulation of ryanodine receptor (RyR) function in intact cells is difficult to measure, because PKA simultaneously increases Ca2+ current (ICa), SR Ca2+ uptake and SR Ca2+ loading (which independently increase SR Ca2+ release). We measured ICa and SR Ca2+ release ± 1 ,m isoproterenol (ISO; isoprenaline) in voltage-clamped ventricular myocytes of rabbits and transgenic mice (expressing only non-phosphorylatable phospholamban). This mouse model helps control for any effect of ISO-enhanced SR uptake on observed release, but the two species produced essentially identical results. SR Ca2+ load and ICa were adjusted by conditioning. We thus evaluated PKA effects on SR Ca2+ release at constant SR Ca2+ load and ICa trigger (with constant unitary ICa). The amount of SR Ca2+ release increased as a function of either ICa or SR Ca2+ load, but ISO did not alter the relationships (measured as gain or fractional release). This was true over a wide range of SR Ca2+ load and ICa. However, the maximal rate of SR Ca2+ release was ,50% faster with ISO (at most loads and ICa levels). We conclude that the isolated effect of PKA on SR Ca2+ release is an increase in maximal rate of release and faster turn-off of release (such that integrated SR Ca2+ release is unchanged). The increased amount of SR Ca2+ release normally seen with ISO depends primarily on increased ICa trigger and SR Ca2+ load, whereas faster release kinetics may be the main result of RyR phosphorylation. [source] Consumer-food systems: why type I functional responses are exclusive to filter feedersBIOLOGICAL REVIEWS, Issue 2 2004Jonathan M. Jeschke ABSTRACT The functional response of a consumer is the relationship between its consumption rate and the abundance of its food. A functional response is said to be of type I if consumption rate increases linearly with food abundance up to a threshold level at which it remains constant. According to conventional wisdom, such type I responses are more frequent among filter feeders than among other consumers. However, the validity of this claim has never been tested. We review 814 functional responses from 235 studies, thereby showing that type I responses are not only exceptionally frequent among filter feeders but that they have only been reported from these consumers. These findings can be understood by considering the conditions that a consumer must fulfil in order to show a type I response. First, the handling condition: the consumer must have a negligibly small handling time (i.e. the time needed for capturing and eating a food item), or it must be able to search for and to capture food while handling other food. Second, the satiation condition: unless its gut is completely filled and gut passage time is minimal, the consumer must search for food at a maximal rate with maximal effort. It thus has to spend much time on foraging (i.e. searching for food and handling it). Our functional response review suggests that only filter feeders sometimes meet both of these conditions. This suggestion is reasonable because filter feeders typically fulfil the handling condition and can meet the satiation condition without losing time, for they are, by contrast to non-filter feeders, able simultaneously to perform foraging and non-foraging activities, such as migration or reproduction. [source] A Review of HNS-32: A Novel Azulene-l-Carboxamidine Derivative with Multiple Cardiovascular Protective ActionsCARDIOVASCULAR THERAPEUTICS, Issue 4 2001Yoshio Tanaka ABSTRACT HNS-32 [N1,N1 -dimethyl- N2 -(2-pyridylmethyl)-5-isopropyl-3,8-dimethylazulene-1-carboxamidine] (CAS Registry Number: 186086-10-2) is a newly synthesized azulene derivative. Computer simulation showed that its three dimensional structure is similar to that of the class Ib antiarrhythmic drugs, e.g., lidocaine or mexiletine. HNS-32 potently suppressed ventricular arrhythmias induced by ischemia due to coronary ligation and/or ischemia-reperfusion in dogs and rats. In the isolated dog and guinea pig cardiac tissues, HNS-32 had negative inotropic and chronotropic actions, prolonged atrial-His and His-ventricular conduction time and increased coronary blood flow. In the isolated guinea pig ventricular papillary muscle, HNS-32 decreased maximal rate of action potential upstroke (V,max) and shortened action potential duration (APD). These findings suggest that HNS-32 inhibits inward Na+ and Ca2+ channel currents. In the isolated pig coronary and rabbit conduit arteries, HNS-32 inhibited both Ca2+ channel-dependent and -independent contractions induced by a wide variety of chemical stimuli. HNS-32 is a potent inhibitor of protein kinase C (PKC)-mediated constriction of cerebral arteries. It is likely to block both, Na+ and Ca2+ channels expressed in cardiac and vascular smooth muscles. These multiple ion channel blocking effects are largely responsible for the antiarrhythmic and vasorelaxant actions of HNS-32. This drug may represent a novel approach to the treatment of arrhythmias. [source] Endothelin-1-mediated coronary vasoconstriction deteriorates myocardial depression in hearts isolated from lipopolysaccharide,treated rats: Interaction with nitric oxideCLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 9 2004Jie Tu Summary 1.,The aim of the present study was to evaluate the contribution of disturbance of coronary perfusion to myocardial depression in hearts isolated from lipopolysaccharide (LPS)-treated rats and to investigate the involvement of endothelin (ET)-1 and nitric oxide (NO). 2.,Rats were treated with LPS (10 mg/kg, i.p.) and, 4 h later, plasma ET-1 concentrations were measured by radioimmunoassay and hearts were excised for perfusion at a constant perfusion flow. The selective ETA receptor antagonist BQ-123, in the absence or presence of aminoguanidine, a specific inhibitor of inducible NO synthase, was given 15 min before LPS challenge. Coronary perfusion pressure (CPP) and measures of myocardial contractile function were recorded. 3.,In hearts isolated from LPS-treated rats, there was a marked increase in CPP that was abolished by pretreatment with BQ-123. In parallel, an increase in plasma ET-1 concentrations was seen in these rats. Lipopolysaccharide also induced decreases in left ventricular developed pressure (LVDP), the product of LVDP and heart rate and maximal rate of rise/fall of left ventricular pressure (+/, dP/dtmax). Single treatment with BQ-123 or aminoguanidine attenuated LPS-induced myocardial depression. However, when these two drugs were given simultaneously, myocardial depression elicited by LPS was blocked significantly. 4.,Endothelin-1-mediated coronary vasoconstriction, together with NO, contributes to myocardial depression in hearts isolated from LPS-treated rats. [source] Reduction of fumarate, mesaconate and crotonate by Mfr, a novel oxygen-regulated periplasmic reductase in Campylobacter jejuniENVIRONMENTAL MICROBIOLOGY, Issue 3 2010Edward Guccione Summary Methylmenaquinol : fumarate reductase (Mfr) is a newly recognized type of fumarate reductase present in some ,-proteobacteria, where the active site subunit (MfrA) is localized in the periplasm, but for which a physiological role has not been identified. We show that the Campylobacter jejuni mfrABE operon is transcribed from a single promoter, with the mfrA gene preceded by a small open reading-frame (mfrX) encoding a C. jejuni -specific polypeptide of unknown function. The growth characteristics and enzyme activities of mutants in the mfrA and menaquinol : fumarate reductase A (frdA) genes show that the cytoplasmic facing Frd enzyme is the major fumarate reductase under oxygen limitation. The Mfr enzyme is shown to be necessary for maximal rates of growth by fumarate respiration and rates of fumarate reduction in intact cells measured by both viologen assays and 1H-NMR were slower in an mfrA mutant. As periplasmic fumarate reduction does not require fumarate/succinate antiport, Mfr may allow more efficient adaptation to fumarate-dependent growth. However, a further rationale for the periplasmic location of Mfr is suggested by the observation that the enzyme also reduces the fumarate analogues mesaconate and crotonate; fermentation products of anaerobes with which C. jejuni shares its gut environment, that are unable to be transported into the cell. Both MfrA and MfrB subunits were localized in the periplasm by immunoblotting and 2D-gel electrophoresis, but an mfrE mutant accumulated unprocessed MfrA in the cytoplasm, suggesting a preassembled MfrABE holoenzyme has to be recognized by the TAT system for translocation to occur. Gene expression studies in chemostat cultures following an aerobic-anaerobic shift showed that mfrA is highly upregulated by oxygen limitation, as would be experienced in vivo. Our results indicate that in addition to a role in fumarate respiration, Mfr allows C. jejuni to reduce analogous substrates specifically present in the host gut environment. [source] Surface Action Potential and Contractile Properties of the Human Triceps Surae Muscle: Effect of ,Dry' Water ImmersionEXPERIMENTAL PHYSIOLOGY, Issue 1 2002Yuri A. Koryak The effects of 7 days of ,dry' water immersion were investigated in six subjects. Changes in the contraction properties were studied in the triceps surae muscle. After immersion, the maximal voluntary contraction (MVC) was reduced by 18.9% (P < 0.01), and the electrically evoked (150 impulses s,1) maximal tension during tetanic contraction (Po) was reduced by 8.2% (P > 0.05). The difference between Po and MVC expressed as a percentage of Po and referred to as force deficiency was also calculated. The force deficiency increased by 44.1% (P < 0.001) after immersion. The decrease in Po was associated with increased maximal rates of tension development (7.2%) and relaxation. The twitch time-to-peak was not significantly changed, and half-relaxation and total contraction time were decreased by 5.3% and 2.8%, respectively, but the twitch tension (Pt) was not significantly changed and the Pt/Po ratio was decreased by 8.7%. The 60 s intermittent contractions (50 impulses s,1) decreased tetanic force to 57% (P < 0.05) of initial values, but force reduction was not significantly different in the two fatigue-inducing tests: fatigue index (the mean loss of force of the last five contractions, expressed as a percentage of the mean value of the first five contractions) was 36.2 ± 5.4% vs. 38.6 ± 2.8%, respectively (P > 0.05). While identical force reduction was present in the two fatigue-inducing tests, it would appear that concomitant electrical failure was considerably different. Comparison of the electrical and mechanical alterations recorded during voluntary contractions, and in contractions evoked by electrical stimulation of the motor nerve, suggests that immersion not only modifies the peripheral processes associated with contraction, but also changes central and/or neural command of the contraction. At peripheral sites, it is proposed that the intracellular processes of contraction play a role in the contractile impairment recorded during immersion. [source] Energy reserves during food deprivation and compensatory growth in juvenile roach: the importance of season and temperatureJOURNAL OF FISH BIOLOGY, Issue 1 2005P. L. M. Van Dijk The effect of 21 days of starvation, followed by a period of compensatory growth during refeeding, was studied in juvenile roach Rutilus rutilus during winter and summer, at 4, 20 and 27° C acclimation temperature and at a constant photoperiod (12L : 12D). Although light conditions were the same during summer and winter experiments and fish were acclimated to the same temperatures, there were significant differences in a range of variables between summer and winter. Generally winter fish were better prepared to face starvation than summer fish, especially when acclimated at a realistic cold season water temperature of 4° C. In winter, the cold acclimated fish had a two to three-fold larger relative liver size with an approximately double fractional lipid content, in comparison to summer animals at the same temperature. Their white muscle protein and glycogen concentration, but not their lipid content, were significantly higher. Season, independent of photoperiod or reproductive cycle, was therefore an important factor that determined the physiological status of the animal, and should generally be taken into account when fish are acclimated to different temperature regimes. There were no significant differences between seasons with respect to growth. Juvenile roach showed compensatory growth at all three acclimation temperatures with maximal rates of compensatory growth at 27° C. The replenishment of body energy stores, which were utilized during the starvation period, was responsible for the observed mass gain at 4° C. The contribution of the different energy resources (protein, glycogen and lipid) was dependent on acclimation temperature. In 20 and 27° C acclimated roach, the energetic needs during food deprivation were met by metabolizing white muscle energy stores. While the concentration of white muscle glycogen had decreased after the fasting period, the concentrations of white muscle lipid and protein remained more or less constant. The mobilization of protein and fat was revealed by the reduced size of the muscle after fasting, which was reflected in a decrease in condition factor. At 20° C, liver lipids and glycogen were mobilized, which caused a decrease both in the relative liver size and in the concentration of these substrates. Liver size was also decreased after fasting in the 4° C acclimated fish, but the substrate concentrations remained stable. This experimental group additionally utilized white muscle glycogen during food deprivation. Almost all measured variables were back at the control level within 7 days of refeeding. [source] Post-translational modifications, but not transcriptional regulation, of major chloroplast RNA-binding proteins are related to Arabidopsis seedling developmentPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 8 2006Bai-Chen Wang Abstract Chloroplast RNA-binding proteins are involved in stabilizing stored chloroplast mRNAs and in recruiting site-specific factors that mediate RNA metabolism. In the present study, we characterized two major chloroplast RNA-binding proteins, cp29A and cp29B, by MALDI-TOF MS, N-terminal sequencing, and ESI-MS/MS following 2D-PAGE separation. Polypeptides derived from cp29A were recovered with free N-terminus or with N-terminal acetylation. In addition to the two isoforms found for cp29A, an isoform derived from cp29B was also observed to have five amino acids cleaved from its N-terminus. Results of quantitative real-time RT-PCR indicate that both genes reached maximal rates of transcription 96,h after commencement of germination and maintained relatively high levels throughout the whole life cycle. Transcription of cp29A and cp29B did not vary significantly under light or dark conditions, although production of the acetylated and N-terminally cleaved protein isoforms exhibited light dependence. Exposure of etiolated Arabidopsis seedlings to light conditions for as short as 9,h restored the modified isoforms to levels similar to those found in green plants. Identification of post-translational modifications in major chloroplast RNA-binding proteins may help elucidate their roles in seedling development and in plant RNA stabilization during the greening process. [source] | |||||||||||||