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1.
Günzel D Galler S 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2000,170(7):523-529
The inhibitory motoneurons of crustaceans form synapses both with the sarcolemma of muscle fibres and with the very distal
branchings of the excitatory motoneurons. The transmitter of these synapses is GABA (γ-aminobutyric acid) which is known to
open Cl− channels. Studies on the dactyl opener muscle of crayfish suggest that application of GABA not only leads to an increase
in the Cl− permeability but also to a considerable HCO−
3 conductance that causes an intracellular acidification. To investigate possible physiological implications, we measured the
intracellular pH of various muscle fibre types of crayfish and crab using pH-sensitive microelectrodes. Independent of the
presence or absence of inhibitory innervation, bath application of 10−5 mol l−1 GABA led to acidification in all fibre types (pH change: 0.14 ± 0.08, n=11). In no preparation was a change in intracellular pH observed upon stimulation of specific or common inhibitory motoneurons
with 10–40 pulses s−1 for 2–5 min. The results suggest that HCO−
3 conductance cannot be activated through synaptic GABA receptors. However, all crustacean muscle fibre types seem to possess
extrasynaptic GABA-sensitive channels that exhibit a considerable HCO−
3 conductance. The physiological importance of these channels remains to be elucidated.
Accepted: 13 July 2000 相似文献
2.
Actual and potential rates of hydrogen photoproduction by continuous culture of the purple non-sulphur bacterium Rhodobacter capsulatus 总被引:1,自引:1,他引:0
A. A. Tsygankov A. S. Fedorov T. V. Laurinavichene I. N. Gogotov K. K. Rao D. O. Hall 《Applied microbiology and biotechnology》1998,49(1):102-107
The influence of (NH4)2SO4 concentration and dilution rate (D) on actual and potential H2 photoproduction has been studied in ammonium-limited chemostat cultures of Rhodobacter capsulatus B10. The actual H2 production in a photobioreactor was maximal (approx. 80 ml h−1 l−1) at D = 0.06 h−1 and 4 mM (NH4)2SO4. However, it was lower than the potential H2 evolution (calculated from hydrogen evolution rates in incubation vials), which amounted to 100–120 ml h−1 l−1 at D = 0.03–0.08 h−1. Taking into account the fact that H2 production in the photobioreactor under these conditions was not limited by light or lactate, another limiting (inhibiting)
factor should be sought. One possibility is an inhibition of H2 production by the H2 accumulated in the gas phase. This is apparent from the non-linear kinetics of H2 evolution in the vials or from its inhibition by the addition of H2; initial rates were restored in both cases after the vials had been refilled with argon. The actual H2 production in the photobioreactor at D = 0.06 h−1 was shown to increase from approximately 80 ml h−1 l−1 to approximately 100 ml h−1 l−1 under an argon flow at 100 ml min−1. Under maximal H2 production rates in the photobioreactor, up to 30% of the lactate feedstock was utilised for H2 production and 50% for biomass synthesis.
Received: 22 April 1997 / Received revision: 14 July 1997 / Accepted: 27 July 1997 相似文献
3.
M. Gleeson N. P. Walsh A. K. Blannin P. J. Robson L. Cook A. E. Donnelly S. H. Day 《European journal of applied physiology and occupational physiology》1998,77(6):543-546
The aim of this study was to determine if severe exercise-induced muscle damage alters the plasma concentrations of glutamine
and zinc. Changes in plasma concentrations of glutamine, zinc and polymorphonuclear elastase (an index of phagocytic cell
activation) were examined for up to 10 days following eccentric exercise of the knee extensors of one leg in eight untrained
subjects. The exercise bout consisted of 20 repetitions of electrically stimulated eccentric muscle actions on an isokinetic
dynamometer. Subjects experienced severe muscle soreness and large increases in plasma creatine kinase activity indicative
of muscle fibre damage. Peak soreness occurred at 2 days post-exercise and peak creatine kinase activity [21714 (6416) U · l−1, mean (SEM)] occurred at 3 days post-exercise (P < 0.01 compared with pre-exercise). Plasma elastase concentration was increased at 3 days post-exercise compared with pre-exercise
(P < 0.05), and is presumably indicative of ongoing phagocytic leucocyte infiltration and activation in the damaged muscles.
There were no significant changes in plasma zinc and glutamine concentrations in the days following eccentric exercise. We
conclude that exercise-induced muscle damage does not produce changes in plasma glutamine or zinc concentrations despite evidence
of phagocytic neutrophil activation.
Accepted: 3 November 1997 相似文献
4.
Bioenergetics and RNA/DNA ratios in the common carp (Cyprinus carpio ) under hypoxia 总被引:2,自引:0,他引:2
Zhou BS Wu RS Randall DJ Lam PK 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2001,171(1):49-57
Hypoxia caused by eutrophication occurs over large areas in aquatic systems worldwide. Common carp (Cyprinus carpio) exposed to hypoxia (1 mg · O2 · l−1 and 2 mg · O2 · l−1) for 1 week showed a significant reduction in feeding rate, respiration rate, faecal production and nitrogenous excretion
compared to those maintained at normoxia (7 mg · O2 · l−1). Fish exposed to hypoxia showed negative scope for growth (SfG), but no significant difference in the specific growth rate
was revealed after 1 week in both hypoxic groups. A significant reduction in RNA/DNA ratio was, however, clearly evident in
the white muscle of the 1 mg · O2 · l−1 treatment group, but not in the 2 mg · O2 · l−1 treatment group. Both specific growth rate and RNA/DNA ratio were significantly reduced when fish were exposed to severe
hypoxia (0.5 mg · O2 · l−1) for 4 weeks. At all levels of hypoxia, growth reduction was accompanied by a significant decrease in RNA/DNA ratio in white
muscle. Covariance analysis showed no significant difference between the slope of RNA/DNA ratio and growth rate under normoxic
conditions and 0.5 mg · O2 · l−1 for 4 weeks (F=1.036, P > 0.326), as well as 1.0 mg · O2 · l−1 and 2.0 mg · O2 · l−1 for 1 week (F = 0.457, P > 0.5), indicating that the RNA/DNA ratio serves as a biomarker of growth under all oxygen levels, at least under controlled
experimental conditions. SfG also appears to be more sensitive than the RNA/DNA ratio in responding to hypoxia in fish.
Accepted: 15 September 2000 相似文献
5.
I. L. Y. Spierts H. A. Akster H. L. Granzier 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(8):543-551
Titin (also known as connectin) is a striated-muscle-specific protein that spans the distance between the Z- and M-lines
of the sarcomere. The elastic segment of the titin molecule in the I-band is thought to be responsible for developing passive
tension and for maintaining the central position of thick filaments in contracting sarcomeres. Different muscle types express
isoforms of titin that differ in their molecular mass. To help to elucidate the relation between the occurrence of titin isoforms
and the functional properties of different fibre types, we investigated the presence of different titin isoforms in red and
white fibres of the axial muscles of carp. Gel electrophoresis of single fibres revealed that the molecular mass of titin
was larger in red than in white fibres. Fibres from anterior and posterior axial muscles were also compared. For both white
and red fibres the molecular mass of titin in posterior muscle fibres was larger than in anterior muscle fibres. Thus, the
same fibre type can express different titin isoforms depending on its location along the body axis. The contribution of titin
to passive tension and stiffness of red anterior and posterior fibres was also determined. Single fibres were skinned and
the sarcomere length dependencies of passive tension and passive stiffness were determined. Measurements were made before
and after extracting thin and thick filaments using relaxing solutions with 0.6 mol · l−1 KCl and 1 mol · l−1 KI. Tension and stiffness measured before extraction were assumed to result from both titin and intermediate filaments, and
tension after extraction from only intermediate filaments. Compared to mammalian skeletal muscle, intermediate filaments developed
high levels of tension and stiffness in both posterior and anterior fibres. The passive tension-sarcomere length curve of
titin increased more steeply in red anterior fibres than in red posterior fibres and the curve reached a plateau at a shorter
sarcomere length. Thus, the smaller titin isoform of anterior fibres results in more passive tension and stiffness for a given
sarcomere strain. During continuous swimming, red fibres are exposed to larger changes in sarcomere strain than white fibres,
and posterior fibres to larger changes in strain than anterior fibres. We propose that sarcomere strain is one of the functional
parameters that modulates the expression of different titin isoforms in axial muscle fibres of carp.
Accepted: 7 May 1997 相似文献
6.
Brian Dawson Martin Fitzsimons Simon Green Carmél Goodman Michael Carey Keith Cole 《European journal of applied physiology and occupational physiology》1998,78(2):163-169
In contrast to endurance training, little research has been carried out to investigate the effects of short (<10 s) sprint
training on performance, muscle metabolism and fibre types. Nine fit male subjects performed a mean of 16 outdoor sprint running
training sessions over 6 weeks. Distances sprinted were 30–80 m at 90–100% maximum speed and between 20 and 40 sprints were
performed in each session. Endurance (maximal oxygen consumption; V˙O2
max), sprint (10 m and 40 m times), sustained sprint (supramaximal treadmill run) and repeated sprint (6 × 40 m sprints, 24 s
recovery between each) performance tests were performed before and after training. Muscle biopsy samples (vastus lateralis)
were also taken to examine changes in metabolites, enzyme activities and fibre types. After training, significant improvements
were seen in 40 m time (P < 0.01), supramaximal treadmill run time (P < 0.05), repeated sprint performance (P < 0.05) and V˙O2
max (P < 0.01). Resting muscle concentrations of ATP and phosphocreatine did not change. Phosphorylase activity increased (P < 0.025), citrate synthase activity decreased (P < 0.01), but no significant changes were recorded in myokinase and phosphofructokinase activities. The proportion of type
II muscle fibres increased significantly (P < 0.05). These results demonstrate that 6 weeks of short sprint training can improve endurance, sprint and repeated sprint
ability in fit subjects. Increases in the proportion of type II muscle fibres are also possible with this type of training.
Accepted: 5 January 1998 相似文献
7.
Protective effects of prostaglandins in the isolated gastric mucosa of the eel, Anguilla anguilla 总被引:1,自引:0,他引:1
Faggio C Denaro MG Lionetto MG Trischitta F 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2000,170(5-6):357-363
The protective effect of endogenous prostaglandins on the fish gastric mucosa was evaluated by studying the effect of indomethacin
and aspirin, known cyclooxigenase inhibitors, on the mucosal ulceration in the isolated gastric sacs of Anguilla anguilla. Gastric sacs devoid of muscle layers were incubated in the presence of indomethacin (10−4 mol · l−1) or aspirin (10−4 mol · l−1) in different experimental conditions. Both the anti-inflammatory drugs produced ulcers, but the effects were more severe
in the presence of histamine and in the absence of HCO3
− in the incubation bath. The effects of prostaglandin E2 (PGE2) on acid secretion rate (JH) and on alkaline secretion rate (JOH) were evaluated (with the aid of the pH stat method) in isolated gastric mucosa mounted in Ussing chambers. We found that
PGE2 (10−8–10−5 mol · l−1) increased JH in a dose-dependent manner. In tissues pretreated with luminal omeprazole (10−4 mol · l−1), PGE2 stimulated gastric alkaline secretion. It was nullified by serosal removal of HCO3
− or Na+ and by serosal ouabain (10−4 mol · l−1). These results suggested that prostaglandins also exert their protective effects in fish gastric mucosa. This protection
seems partially due to a stimulation of exogenous HCO3
− transport from the serosal to the mucosal side. It is likely that this transport is an active transcellular mechanism coupled
to Na+ transport.
Accepted: 14 April 2000 相似文献
8.
YongXia Wang XiuAn Zhan XiWen Zhang RuJuan Wu Dong Yuan 《Biological trace element research》2011,143(1):261-273
This study was conducted to investigate the effects of different sources of dietary selenium (Se) supplementation on growth
performance, meat quality, Se deposition, and antioxidant property in broilers. A total of 600 one-day-old Ross 308 broilers
with an average body weight (BW) of 44.30 ± 0.49 g were randomly allotted to three treatments, each of which included five
replicates of 40 birds. These three groups received the same basal diet containing 0.04 mg Se/kg, supplemented with 0.15 mg
Se/kg from sodium selenite (SS) or from l-selenomethionine (l-Se-methionine (Met)) or from d-selenomethionine (d-Se-Met). The experiment lasted 42 days. Both Se source and time significantly influenced (p < 0.01) drip loss of breast muscle. Supplementation with l-Se-Met and d-Se-Met were more effective (p < 0.05) in decreasing drip loss than SS. Besides, the pH value of breast muscle was also significantly influenced (p < 0.05) by time. The SS-supplemented diet increased more (p < 0.05) liver, kidney, and pancreas glutathione peroxidase (GSH-Px) activities than the d-Se-Met-supplemented diet. In addition, l-Se-Met increased more (p < 0.01) liver and pancreas GSH-Px activities than d-Se-Met. The antioxidant status was greatly improved in broilers of l-Se-Met-treated group in comparison with the SS-treated group and was illuminated by the increased glutathione (GSH) concentration
in serum, liver, and breast muscle (p < 0.05); superoxide dismutase (SOD) activity in liver (p < 0.01); total antioxidant capability (T-AOC) in kidney, pancreas, and breast muscle (p < 0.05) and decreased malondialdehyde (MDA) concentration in kidney and breast muscle (p < 0.05) of broilers. Besides, supplementation with d-Se-Met was more effective (p < 0.01) in increasing serum GSH concentration and decreasing breast muscle MDA concentration than SS. l-Selenomethionine supplementation significantly increased GSH concentration in liver and breast muscle (p < 0.05); SOD activity in liver (p < 0.01); and T-AOC in liver, pancreas, and breast muscle (p < 0.05) of broilers, compared with broilers fed d-Se-Met diet. The addition of l-Se-Met and d-Se-Met increased (p < 0.01) Se concentration in serum and different organs studied of broilers in comparision with broilers fed SS diet. Therefore,
dietary l-Se-Met and d-Se-Met supplementation could improve antioxidant capability and Se deposition in serum and tissues and reduce drip loss of
breast muscle in broilers compared with SS. Besides, l-Se-Met is more effective than d-Se-Met in improving antioxidant status in broilers. 相似文献
9.
Carmel M. McEniery David G. Jenkins Christopher Barnett 《European journal of applied physiology and occupational physiology》1997,75(5):462-466
The present study investigated the relationship between plasma potassium ion concentration ([K+]) and skeletal muscle torque during three different 15-min recovery periods after fatigue induced by four 30-s sprints. Four
males and one female completed the multiple sprint exercise on three separate days; recovery was passive, i.e. no cycling
exercise (PRec), active cycling at 30% peak oxygen consumption O2peak (30% Rec) and active cycling at 60% O2peak (60% Rec). Plasma [K+] was measured from blood sampled from an antecubital vein of subjects at rest and at 0, 3, 5, 10 and 15 min into each recovery.
Isokinetic leg strength was measured at rest and at 1, 6, 11 and 16 min during each recovery. Following the exhaustive sprints,
[K+] increased significantly from an average mean (SEM) resting value of 3.81 (0.07) mmol · l−1 to 4.48 (0.19) mmol · l−1 (P < 0.01). In all recovery conditions, plasma [K+] returned to resting levels within 3 min following the fourth sprint. However, in the two active recovery conditions plasma
[K+] increased over the remainder of the recovery periods to 4.36 (0.12) mmol · l−1 in the 30% Rec condition and 4.62 (0.12) mmol · l−1 in the 60% Rec condition, the latter being significantly higher than the former (P < 0.01). The maximum torque measured following the sprints decreased significantly, on average, to 61.1 (8.36)% of peak levels
(P < 0.01). After 15 min of recovery, maximum torque was highest in the 30% Rec condition at 92.13 (3.06)% of peak levels (P < 0.01), compared to 85.23 (3.64)% and 85.71 (0.82)% for the PRec and 60% Rec conditions, respectively. In contrast to the
significant differences in plasma [K+] across all three recovery conditions, muscle torque recovery was significantly different in only the 30% Rec condition.
In summary, recovery of peak levels of muscle torque following fatiguing exercise does not appear to follow changes in plasma
[K+].
Accepted: 18 October 1996 相似文献
10.
A fluidized-bed reactor (FBR) was used to enrich an aerobic chlorophenol-degrading microbial culture. Long-term continuous-flow
operation with low effluent concentrations selected oligotrophic microorganisms producing good-quality effluent for pentachlorophenol(PCP)-contaminated
water. PCP biodegradation kinetics was studied using this FBR enrichment culture. The results from FBR batch experiments were
modeled using a modified Haldane equation, which resulted in the following kinetic constants: q
max = 0.41 mg PCP mg protein−1 day−1, K
S = 16 μg l−1, K
i = 5.3 mg l−1, and n = 3.5. These results show that the culture has a high affinity for PCP but is also inhibited by relatively low PCP concentrations
(above 1.1 mg PCP l−1). This enrichment culture was maintained over 1 year of continuous-flow operation with PCP as the sole source of carbon and
energy. During continuous-flow operation, effluent concentrations below 2 μg l−1 were achieved at 268 min hydraulic retention time (t
HR) and 2.5 mg PCP l−1 feed concentration. An increase in loading rate by decreasing t
HR did not significantly deteriorate the effluent quality until a t
HR decrease from 30 min to 21 min resulted in process failure. Recovery from process failure was slow. Decreasing the feed PCP
concentration and increasing t
HR resulted in an improved process recovery.
Received: 10 October 1996 / Received revision: 21 January 1997 / Accepted: 24 January 1997 相似文献
11.
A model of the muscle fibre extracellular action potentials (ECAPs) calculation using experimentally recorded intracellular
action potentials (ICAPs) has been applied to investigate the effect of repetitive stimulation on the electrical activity
of isolated frog muscle fibres. The ECAPs were calculated both at small (0.01 mm) and at large (5 mm) radial distances to
the fibre axis, and their relationship with the original ICAP parameters has been inferred. Fourier transformation of the
calculated ECAPs in order to obtain the spectral characteristics and to trace out their behaviour during continuous fibre
activity was performed. Stimulation frequency dependence on the ECAP time characteristics and on the shift of the maximum
spectral density towards low frequencies at small and large radial distance were observed. The spectral density peak frequency
is propagation velocity (PV)-dependent. The advantage of the presented method over the available experimental extracellular
recording techniques from isolated muscle fibers is the possibility to show the effect of continuous muscle fibre activity
on the parameters of the ECAPs and their spectral characteristics at large radial distance, which is not experimentally accessible.
Our results are in agreement with those experimentally obtained. The results from the model prove the role of changes in PV
of excitation along the muscle fibres (representing the last link in the complex organized motor system) in the development
of fatigue.
Received: 24 July 1997 / Accepted in revised form: 2 July 1998 相似文献
12.
T. J. Wright H. Huddart 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1999,169(8):561-568
Buccal mass muscle of the pest slug Deroceras reticulatum was examined by conventional tension recording and the sucrose-gap electrophysiological technique. Elevated potassium salines
induced dose-dependent depolarisations accompanied by tonic contractures with superimposed rapid twitch contractions. The
latter were suppressed at over 40 mmol · l−1 external potassium, where depolarisation-induced inactivation of voltage-sensitive calcium channels may have occurred. Acetylcholine
caused significant dose-dependent depolarisations and tonic contractures, while 5-hydroxy tryptamine induced lower depolarisations
accompanied by phasic contractile activity superimposed on low level tonic force. Of the purines examined only guanosine triphosphate
caused significant mechanical activity above a threshold of 0.1 μmol · l−1. The tetrapeptides inhibited buccal muscle spontaneous activity, but the related small cardioactive peptide B was weakly
excitatory. The amino acids glutamate and gamma-aminobutyric acid were weakly excitatory on buccal muscle while the molluscicides
metaldehyde and methiocarb disrupted normal mechanical activity of the feeding musculature. Acetylcholine and 5-hydroxytryptamine
appear to have major roles in regulating feeding muscle activity, seemingly modulated by guanosine triphosphate and inhibited
by phenylalanine-methionine-arginine-phenylalanine-NH2 and phenylalanine-leucine-arginine-phenylalanine-NH2.
Accepted: 22 July 1999 相似文献
13.
Inhibition of Clostridium butyricum by 1,3-propanediol and diols during glycerol fermentation 总被引:3,自引:0,他引:3
1,3-Propanediol inhibition during glycerol fermentation to 1,3-propanediol by Clostridium butyricum CNCM 1211 has been studied. The initial concentration of the 1,3-propanediol affected the growth of the bacterium more than
the glycerol fermentation. μ
max was inversely proportional to the initial concentration of 1,3-propanediol (0–65 g l−1). For glycerol at 20 g l−1, the growth and fermentation were completely stopped at an initial 1,3-propanediol concentration of 65 g l−1. However, for an initial 1,3-propanediol concentration of 50 g l−1 and glycerol at 70 g l−1, the final concentration (initial and produced) of 1,3-propanediol reached 83.7 g l−1(1.1 M), with complete consumption of the glycerol. Therefore, during the fermentation, the strain tolerated a 1,3-propanediol
concentration higher than the initial inhibitory concentration (65 g l−1). The addition of 1,2-propanediol or 2,3-butanediol (50 g l−1) in the presence of glycerol (50–100 g l−1), showed that 2-diols reduced the μ
max in a similar way to 1,3-propanediol. The measurement of the osmotic pressure of glycerol solutions, diols and diol/glycerol
mixtures did not indicate any differences between these compounds. The hypothesis of diol inhibition was discussed. Taking
into account the strain tolerance of highly concentrated 1,3-propanediol during fermentation, the fermentation processes for
optimising production were considered.
Received: 15 November 1999 / Revision received: 1 February 2000 / Accepted: 4 February 2000 相似文献
14.
S. Morris J. Callaghan 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1998,168(5):389-398
The Australian Yabby Cherax destructor voluntarily emerges from water to breathe air with increased frequency as water PO2 decreases. When the water PO2 declined below 2.7 kPa the crayfish spent >50% of time breathing air. The respiratory gas transport, acid-base, ionic and
energetic status were quantified in simulations of this emersion behaviour to determine the benefits that the crayfish may
gain from switching to air-breathing. C. destructor initially showed an elevated O2 uptake rate on emerging from hypoxic water, but after 1 h the O2 uptake rate was not different from that of crayfish in normoxic water. During 3 h of air breathing, subsequent to 2.7 kPa
aquatic hypoxia, the haemolymph PO2 increased while oxygen content was essentially unchanged, although cardiac output increased 5-fold. The haemolymph PCO2 increased from 0.44 to 1.21 kPa after 3 h while the CO2 content increased from 3.47 to 8.66 mmol · l−1 and the pH decreased from 7.73 to 7.57 after 1 h in air. In air C. destructor eventually achieved an O2 uptake rate similar to that achieved in water. A general hyperglycaemia occurred without anaerobiosis. In air-breathing C. destructor, small changes in lactate appear to offset the decrease in haemocyanin-O2 affinity caused by acid Bohr shift. During air-breathing, decreased haemocyanin-O2 affinity assisted in maintaining O2 diffusion into the tissues, but the ATP content of the tail muscle decreased so that after 3 h in air the energy charge was
only 0.59. The data are consistent with a specific depression of the Emden-Meyerhof pathway, preventing either lactate formation
or oxidative phosphorylation in the tail muscle, despite a concomitant glycogenolysis.
Accepted: 26 February 1998 相似文献
15.
The effects of elevated CO2 concentrations on stomatal movement, anion- and K+-channel activities were examined in guard cells from epidermal strips of Vicia faba. Membrane voltage was measured using intracellular, double-barrelled microelectrodes and ion-channel currents were recorded
under voltage clamp during exposure to media equilibrated with ambient (350 μl · l−1), 1000 μl · l−1 and 10 000 μl · l−1 CO2 in 20% O2 and 80% N2. The addition of 1000 μl · l−1 CO2 to the bathing solution caused stomata to close with a halftime of approx. 40 min, and with 10 000 μl · l−1 CO2 closure occurred with a similar time course. Under voltage clamp, exposure to 1000 μl · l−1 and 10 000 μl · l−1 CO2 resulted in a rapid increase (mean, 1.5 ± 0.2-fold, n = 8; range 1.3- to 2.5-fold) in the magnitude of current carried by outward-rectifying K+ channels (IK,out). The effect of CO2 on IK,out was essentially complete within 30 s and was independent of clamp voltage, but was associated with 25–40% (mean, 30 ± 4%)
decrease in the halftime for current activation. Exposure to CO2 also resulted in a four-fold increase in background current near the free-running membrane voltage, recorded as the instantaneous
current at the start of depolarising and hyperpolarising voltage steps, and a decrease in the magnitude of current carried
by inward-rectifying K+ channels (IK,in). The effect of CO2 on IK,in was generally slower than on IK,out; it was allied with a transient acceleration of its activation kinetics during the first 60–120 s of treatment; and it was
associated with a negative shift in the voltage-sensitivity of gating over a period of 3–5 min. Measurements carried out to
isolate the background currents attributable to anion channels (ICl), using tetraethylammonium chloride and CsCl, showed that CO2 also stimulated ICl and dramatically altered its relaxation kinetics. Within the timeframe of CO2 action at the membrane, no significant effect was observed on cytosolic pH, measured using the fluorescent dye 2′,7′-bis-(2-carboxyethyl)-5,6-carboxyflourescein
(BCECF) and ratio fluorescence microphotometry. These results are broadly consistent with the pattern of guard-cell response
to abscisic acid, and indicate that guard cells control both anion and K+ channels to achieve net solute loss in CO2. By contrast with the effects of abscisic acid, however, the data indicate that CO2 action is not mediated through changes in cytosolic pH and thereby implicate new and, as yet, unidentified pathway(s) for
channel regulation in the guard cells.
Received: 8 January 1997 / Accepted: 28 February 1997 相似文献
16.
J. Langfort R. Zarzeczny W. Pilis K. Nazar H. Kaciuba-Ucitko 《European journal of applied physiology and occupational physiology》1997,76(2):128-133
The aim of this study was to find out whether a low-carbohydrate diet (L-CHO) affects: (1) the capacity for all-out anaerobic
exercise, and (2) hormonal and metabolic responses to this type of exercise. To this purpose, eight healthy subjects underwent
a 30-s bicycle Wingate test preceded by either 3 days of a controlled mixed diet (130 kJ/kg of body mass daily, 50% carbohydrate,
30% fat, 20% protein) or 3 days of an isoenergetic L-CHO diet (up to 5% carbohydrate, 50% fat, 45% protein) in a randomized
order. Before and during 1 h after the exercise venous blood samples were taken for measurement of blood lactate (LA), β-hydroxybutyrate
(β-HB), glucose, adrenaline (A), noradrenaline (NA) and insulin levels. Oxygen consumption (V˙O2) was also determined. It was found that the L-CHO diet diminished the mean power output during the 30-s exercise bout [533
(7) W vs 581 (7) W, P < 0.05] without changing the maximal power attained during the first or second 5-s interval of the exercise. In comparison
with the data obtained after the consumption of a mixed diet, after the consumption of a L-CHO diet resting plasma concentrations
of β-HB [2.38 (0.18) vs 0.23 (0.01) mmol · l−1, P < 0.001] and NA [4.81 (0.68) vs 2.2 (0.31) nmol · l−1, P < 0.05] were higher, while glucose [4.6 (0.1) vs 5.7 (0.2) mmol · l−1, P < 0.05] and insulin concentrations [11.9 (0.9) vs 21.8 (1.8) mU · l−1] were lower. The 1-h post-exercise excess of V˙O2 [9.1 (0.25) vs 10.6 (0.25) l, P < 0.05], and blood LA measured 3 min after the exercise [9.5 (0.4) vs 10.6 (0.5) mmol · l−1, P < 0.05] were lower following the L-CHO treatment, whilst plasma NA and A concentrations reached higher values [2.24 (0.40) vs
1.21 (0.13) nmol · l−1 and 14.30 (1.41) vs 8.20 (1.31) nmol · l−1, P < 0.01, respectively]. In subjects on the L-CHO diet, the plasma β-HB concentration decreased quickly after exercise, attaining
≈30% of the pre-exercise value within 60 min, while insulin and glucose levels were elevated. The main conclusions of this
study are: (1) a L-CHO diet is detrimental to anaerobic work capacity, possibly because of a reduced muscle glycogen store
and decreased rate of glycolysis; (2) reduced carbohydrate intake for 3 days enhances activity of the sympathoadrenal system
at rest and after exercise.
Accepted: 31 January 1997 相似文献
17.
Continuous production of l(+)-lactic acid by Lactobacillus casei in two-stage systems 总被引:2,自引:0,他引:2
Bruno-Bárcena JM Ragout AL Córdoba PR Siñeriz F 《Applied microbiology and biotechnology》1999,51(3):316-324
A two-stage two-stream chemostat system and a two-stage two-stream immobilized upflow packed-bed reactor system were used
for the study of lactic acid production by Lactobacillus casei subsp casei. A mixing ratio of D
12/D
2 = 0.5 (D = dilution rate) resulted in optimum production, making it possible to generate continuously a broth with high lactic acid
concentration (48 g l−1) and with a lowered overall content of initial yeast extract (5 g l−1), half the concentration supplied in the one-step process. In the two-stage chemostat system, with the first stage at pH
5.5 and 37 °C and a second stage at pH 6.0, a temperature change from 40 °C to 45 °C in the second stage resulted in a 100%
substrate consumption at an overall dilution rate of 0.05 h−1. To increase the cell mass in the system, an adhesive strain of L. casei was used to inoculate two packed-bed reactors, which operated with two mixed feedstock streams at the optimal conditions
found above. Lactic acid fermentation started after a lag period of cell growth over foam glass particles. No significant
amount of free cells, compared with those adhering to the glass foam, was observed during continuous lactic acid production.
The extreme values, 57.5 g l−1 for lactic acid concentration and 9.72 g l−1 h−1 for the volumetric productivity, in upflow packed-bed reactors were higher than those obtained for free cells (48 g l−1 and 2.42 g l−1 h−1) respectively and the highest overall l(+)-lactic acid purity (96.8%) was obtained in the two-chemostat system as compared with the immobilized-cell reactors (93%).
Received: 4 December 1997 / Received revision: 23 February 1998 / Accepted: 14 March 1998 相似文献
18.
Navas CA James RS Wakeling JM Kemp KM Johnston IA 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1999,169(8):588-596
The aims of this study were: (1) to analyze individual variation in frog locomotor performance, (2) to compare the thermal
sensitivity of jumping and swimming, and (3) to contrast whole animal versus muscle fiber performance at different temperatures.
The jumping and swimming performance of Rana temporaria was analyzed at 5, 10, 15 and 20 °C. Muscle fiber bundles were isolated from lateral gastrocnemius and subjected to the length
and activation patterns thought to occur in vivo. As temperature increased, locomotor performance in R. temporaria improved with a Q
10 of 1.2 for both jump take-off velocity and mean swimming velocity. The slope of the relationship between performance and
temperature (TE) was similar for both locomotor parameters and was described by the equation z-scores of locomotor performance = 0.127 × TE − 1.585. Although some frogs performed better than others relative performance was affected by locomotor type and temperature.
Locomotor performance improved with temperature as the power required during take-off and the mean muscle power output increased
with Q
10 values of 1.7 and 1.6 respectively. The mean muscle power output during take-off was only 34% of the calculated requirements
for the whole animal, suggesting the involvement of elastic strain energy storage mechanisms.
Accepted: 2 September 1999 相似文献
19.
J. M. Holmes A.-S. Gräns D. M. Neil S. P. Baden 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1999,169(6):402-410
The effects of the metal ions manganese and cobalt on force production by the abdominal superficial flexor muscle of the
Norway lobster, Nephrops norvegicus, have been studied in response to both neuronal stimulation and electrical field stimulation applied to an isolated neuromuscular
preparation, and by selectively blocking synaptic transmission with ivermectin. In response to both forms of stimulation,
low concentrations of manganese added to the standard N. norvegicus saline increased the contractile force produced by the muscle, whereas higher concentrations of manganese inhibited both
responses in a dose-dependent manner, until force was completely abolished at concentrations above 2.9 mM manganese. Cobalt
ions produced similar effects, and no significant difference was found between the concentration of the two ions at 50% force
inhibition (Km) or between the two stimulation methods (manganese: 1.22 mM; cobalt: 1.29 mM, P = 0.86). This suggests that they have a similar mode of action, and a postsynaptic site of inhibition. These Km values are considerably higher than the concentrations of these ions known to accumulate in the haemolymph of N.
norvegicus under eutrophic conditions, and it therefore seems unlikely that accumulations of manganese or cobalt ions under such conditions
would cause any significant inhibition of muscle contraction force.
Accepted: 28 April 1999 相似文献
20.
Production of sophorolipids from whey 总被引:5,自引:0,他引:5
Otto RT Daniel HJ Pekin G Müller-Decker K Fürstenberger G Reuss M Syldatk C 《Applied microbiology and biotechnology》1999,52(4):495-501
Sophorolipids, obtained by a two-stage process starting from deproteinized whey concentrate using Cryptococcus curvatus ATCC 20509 and Candida bombicola ATCC 22214, were compared to products from one-stage processes, using different lipidic compounds as substrates. Results
showed that above all carbon source and not cultivation conditions had a distinct influence on the composition of the crude
product mixture and therefore on the physicochemical and biological properties of the sophorolipids, such as, for example,
surface activity, cytotoxicity and stability against hydrolases. The results were completed by corresponding data for purified
mono- and diacetylated (17-hydroxyoctadecenoic)-1′,4′′-lactonized sophorolipids. Crude sophorolipid mixtures showed moderate
to good surface active properties (SFTmin 39 mN m−1, CMC 130 mg l−1), water solubilities (2–3 g l−1) and low cytotoxicities (LC50 300–700 mg l−1). In contrast, purified sophorolipids were more surface active (SFTmin 36 mN m−1, CMC 10 mg l−1), less water soluble (max. 70 mg l−1) and showed stronger cytotoxic effects (LC50 15 mg l−1). Incubation of crude sophorolipid mixtures with different hydrolases demonstrated that treatment with commercially available
lipases such as from Candida rugosa and Mucor miehei distinctly reduced the surface active properties of the sophorolipids, while treatment with porcine liver esterase and glycosidases
had no effect.
Received: 23 February 1999 / Received revision: 27 May 1999 / Accepted: 28 May 1999 相似文献