共查询到20条相似文献,搜索用时 15 毫秒
1.
S. M. E. Guirguis J. C. Yee D. F. Stiffler 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(5):328-334
The skin of intact, free-swimming Xenopus laevis transports Ca2+ inwardly in a manner that is proportional to the external [Ca2+] up to about 0.3 mmol · l−1, saturates above 0.3 mmol · l−1, and is opposed to the electrochemical gradient. Efflux is relatively constant at external concentrations between 0.016 and
0.6 mmol · l−1; net flux which is negative below 0.125 mmol · l−1 becomes positive above this external [Ca2+]. Allometric analysis suggests that both Ca2+ influx and efflux scale to the 2/3 power approximately like surface area. There were no significant differences in influx
between summer and fall animals; however, efflux was greater in the fall and this resulted in a change from positive balance
in the summer to negative balance in the fall. Isolated skins were shown to support a Ca2+ uptake rate of nearly 30 nmol · cm−2 · h−1. The phenylalkylamine verapamil in the apical bathing solution significantly inhibited this at 25 μmol · l−1. The benzothiazepine diltiazem was also effective at 50 μmol · l−1 while the dihydropyradine nifedipine was ineffective up to 100 μmol · l−1. The inorganic ion La3+ was effective at blocking Ca2+ uptake at 300 μmol · l−1; Ni2+ was also effective at 500 μmol · l−1 but Co2+ was ineffective up to 500 μmol · l−1. These results suggest that apical calcium channels in Xenopuslaevis skin have properties similar to mammalian L-channels and fish gill Ca2+ channels.
Accepted: 23 January 1997 相似文献
2.
T. H. Dietz D. H. Neufeld H. Silverman S. H. Wright 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1998,168(2):87-95
The effect of ambient osmolality on the height of lateral ciliated cells from the gills of two freshwater bivalve species
(Dreissena polymorpha, Toxolasma texasensis) was directly observed microscopically. The addition of 1 mmol · l−1 KCl to an artificial pondwater (APW) superfusion medium resulted in an increase in cell height. When the superfusion solution
was made hyperosmotic (∼90 mmol · kg−1 H2O) by the addition of 45 mmol · l−1 NaCl to APW, the cell height decreased by about 20–30% and there was no evidence of a regulatory volume increase over 20–30 min.
In contrast, when 1 mmol · l−1 KCl was added to the hyperosmotic medium the cell height always partially (40–50%) recovered. When the gill tissue was returned
to APW following the hyperosmotic treatment the cells returned to the original cell height. Bivalve gills superfused with
the hyperosmotic NaCl and KCl solution in the presence of 1 mmol · l−1 ouabain experienced a similar 25% decrease in cell height. When the ouabain-treated tissues were returned to APW the cells
swelled, overshooting the original cell height. These results indicate these freshwater bivalves have a limited ability for
cellular volume regulation using inorganic ions, but depend on a suitable balance of Na+ and K+ in the environment to effect regulatory volume changes.
Accepted: 17 October 1997 相似文献
3.
Moro D Bradshaw SD 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1999,169(8):538-548
A laboratory study investigated the metabolic physiology, and response to variable periods of water and sodium supply, of
two arid-zone rodents, the house mouse (Mus domesticus) and the Lakeland Downs short-tailed mouse (Leggadina lakedownensis) under controlled conditions. Fractional water fluxes for M. domesticus (24 ± 0.8%) were significantly higher than those of L. lakedownensis (17 ± 0.7%) when provided with food ad libitum. In addition, the amount of water produced by M. domesticus and by L. lakedownensis from metabolic processes (1.3 ± 0.4 ml · day−1 and 1.2 ± 0.4 ml · day−1, respectively) was insufficient to provide them with their minimum water requirement (1.4 ± 0.2 ml · day−1 and 2.0 ± 0.3 ml · day−1, respectively). For both species of rodent, evaporative water loss was lowest at 25 °C, but remained significantly higher
in M. domesticus (1.1 ± 0.1 mg H2O · g−0.122 · h−1) than in L. lakedownensis (0.6 ± 0.1 mg H2O · g−0.122 · h−1). When deprived of drinking water, mice of both species initially lost body mass, but regained it within 18 days following
an increase in the amount of seed consumed. Both species were capable of drinking water of variable saline concentrations
up to 1 mol · l−1, and compensated for the increased sodium in the water by excreting more urine to remove the sodium. Basal metabolic rate
was significantly higher in M. domesticus (3.3 ± 0.2 mg O2 · g−0.75 · h−1) than in L. lakedownensis (2.5 ± 0.1 mg O2 · g−0.75 · h−1). The study provides good evidence that water flux differences between M. domesticus and L. lakedownensis in the field are due to a requirement for more water in M. domesticus to meet their physiological and metabolic demands. Sodium fluxes were lower than those observed in free-ranging mice, whose
relatively high sodium fluxes may reflect sodium associated with available food.
Accepted: 16 August 1999 相似文献
4.
Characteristics of dipeptide transport in pig jejunum in vitro 总被引:4,自引:0,他引:4
Winckler C Breves G Boll M Daniel H 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1999,169(7):495-500
Characteristics of dipeptide transport in pig jejunum were investigated in vitro by applying the Ussing-chamber technique
and mucosal uptake studies. Addition of both glycyl-l-glutamine and glycyl-l-sarcosine (20 mmol · l−1) to the mucosal buffer solution significantly increased the short-circuit current by 2.60 ± 0.15 and 1.57 ± 0.20 μeq · cm−2 · h−1, respectively. Concentration-dependent changes in short-circuit current followed Michaelis-Menten kinetics with similar affinity
constants for both dipeptides. From unidirectional flux rates for radiolabelled glycyl-l-sarcosine, a net flux rate for glycyl-l-sarcosine of 49.8 ± 6.7 nmol · cm−2 · h−1 was calculated. In mucosal uptake experiments, the apical influx of 14C-labelled glycyl-l-sarcosine into isolated porcine mucosa was pH dependent and significantly inhibited by glycyl-l-glutamine. Moreover, RT-PCR studies with primers derived from rabbit PepT1 identified two PCR fragments of identical size
to rabbit PepT1 from pig intestinal mRNA preparations. In conclusion, our studies revealed key features of mammalian intestinal
peptide transporters and give evidence for a PepT1-like transporter in the pig jejunum that could significantly contribute
to the overall amino acid absorption from the gut.
Accepted: 30 June 1999 相似文献
5.
M. E. Forster W. Davison M. Axelsson L. Sundin C. E. Franklin S. Gieseg 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1998,168(5):345-352
Two species of Antarctic fish were stressed by moving them from seawater at −1 °C to seawater at 10 °C and holding them for
a period of 10 min. The active cryopelagic species Pagothenia borchgrevinki maintained heart rate while in the benthic species Trematomus bernacchii there was an increase in heart rate. Blood pressure did not change in either species. Both species released catecholamines
into the circulation as a consequence of the stress. P. borchgrevinki released the greater amounts, having mean plasma concentrations of 177 ± 54 nmol · l−1 noradrenaline and 263 ± 131 nmol · l−1 adrenaline at 10 min. Plasma noradrenaline concentrations rose to 47 ± 14 nmol · l−1 and adrenaline to 73 ± 28 nmol · l−1 in T. bernacchii. Blood from P. borchgrevinki was tonometered in the presence of isoprenaline. A fall in extracellular pH suggests the presence of a Na+/H+ antiporter on the red cell membrane, the first demonstration of this in an Antarctic fish. Treatment with the β-adrenergic
antagonist drug sotalol inhibited swelling of red blood cells taken from temperature-stressed P. borchgrevinki, suggesting that the antiporter responds to endogenous catecholamines.
Accepted: 22 January 1998 相似文献
6.
Theodore J. Angelopoulos Rebecca Lewis Thanassis Jamurtas Chris Schumann 《European journal of applied physiology and occupational physiology》1998,77(6):556-559
We characterized the effect of ten days of training on lipid metabolism in 6 [age 37.2 (2.3) years] sedentary, obese [BMI
34.4 (3.0) kg · m−2] males with normal glucose tolerance. An oral glucose tolerance test was performed prior to and at the end of the 10 d of
training period. The duration of each daily exercise session was 40 min at an intensity equivalent to ˜75% of the age predicted
maximum heart rate. Blood measurements were performed after an overnight fast, before and at the end of the 10 d period. Plasma
triacylglycerol was significantly (p < 0.05) reduced following exercise training (2.15 ± 0.29 vs. 1.55 ± 0.28 mmol · l−1). Very low density lipoprotein-triacylglycerol was also significantly (p < 0.05) reduced (1.82 ± 0.3 vs. 1.29 ± 0.29 mmol · l−1). No significant changes in high density lipoprotein-cholesterol were observed as a result of training. Following training
fasting plasma glucose and fasting plasma insulin were significantly reduced [Glucose: 5.9 (0.2) mmol · l−1 vs. 5.3 (0.22) mmol · l−1 (p < 0.05); Insulin 264.3 (53.8) ρ · mol · l−1 vs. 200.9 (30.1) ρ · mol · l−1, p = 0.05]. The total area under the glucose curve during the OGTT decreased significantly (p < 0.05). These preliminary data suggest that short-term exercise, without concomitant loss of body mass, induces favorable
changes in plasma triacylglycerol, and very low density lipoprotein-triacylglycerol and glucose tolerance but has no effect
on high density lipoproteincholesterol.
Accepted: 7 January 1998 相似文献
7.
Hans Gesser William R. Driedzic Francisco Tadeu Rantin José Carlos de Freitas 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(7):474-480
Isometric force development of electrically paced preparations isolated from the systemic heart of Octopus vulgaris were utilized to examine the regulation of contractility by Ca2+. Increases in extracellular Ca2+, to the physiological level, resulted in enhancement of twitch force. For instance, at 36 beats · min−1 an increase in Ca2+ from 3 to 9 mmol · l−1 resulted in a threefold increase in twitch force development. When steady-state contraction at 12 beats · min−1 was followed by a rest period of either 5 or 10 min, the first contraction always exhibited either an increase in twitch
force or stayed unchanged such that post-rest twitch force was about 133% of the last value in the steady-state train. Ryanodine
(12.5 μmol · l−1), which is considered to be a specific inhibitor of the Ca2+ storage and release capabilities of the sarcoplasmic reticulum (SR), was applied to further assess Ca2+ handling. Twitch force fell to about 22% of the preteatment level in preparations paced at either 12 or 36 beats · min−1. In all preparations the frequency transition from 12 to 36 beats · min−1 was associated with an increase in resting tension. The␣increase␣was 37 ± 14% prior to ryanodine treatment and was significantly
elevated to 127 ± 33% following treatment. When steady-state contraction at 36 beats · min−1 was followed by a rest period of 10 s, the first contraction was not significantly different from the last beat in the train
prior to ryanodine; however, with ryanodine treatment, post-rest twitch force development significantly decreased. Twitch
force development was regular at pacing rates of up to 300 beats · min−1. Twitch force was maintained up to rates of 84 beats · min−1 but␣decreased thereafter and reached a value of about 10% at 300 beats · min−1. Resting tension increased substantially as frequency was elevated from 12 to 36 beats · min−1 and then gradually increased as frequency was further elevated to 180 beats · min−1. In conclusion, the Octopus ventricle is dependent upon extracellular Ca2+ for contraction. A post-rest potentiation of force development, the negative impact of ryanodine, and the ability to respond
regularly at high pacing rates imply a strong reliance on the SR in Ca2+ cycling based on criteria established for vertebrate hearts.
Accepted: 19 January 1997 相似文献
8.
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
9.
Active excretion of ammonia across the gills of the shore crab Carcinus maenas and its relation to osmoregulatory ion uptake 总被引:1,自引:0,他引:1
D. Weihrauch W. Becker U. Postel S. Riestenpatt D. Siebers 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1998,168(5):364-376
The mechanism of transbranchial excretion of total ammonia of brackish-water acclimated shore crabs, Carcinus maenas was examined using isolated, perfused gills. Applying physiological gradients of NH4Cl (100–200 μmol · l−1) directed from the haemolymph space to the bath showed that the efflux of total ammonia consisted of two components. The
saturable component (excretion of NH4
+) greatly exceeded the linear component (diffusion of NH3). When an outwardly directed gradient (200 μmol · l−1) was applied, total ammonia in the perfusate was reduced by more than 50% during a single passage of saline through the gill.
Effluxes of ammonia along the gradient were sensitive to basolateral dinitrophenol, ouabain, and Cs+ and to apical amiloride. Acetazolamide (1 mmol · l−1 basolateral) or Cl−-free conditions had no substantial effects on ammonia flux, which was thus independent of both carbonic anhydrase mediated
pH regulation and osmoregulatory NaCl uptake. When an inwardly directed gradient (200 μmol · l−1) was employed, influx rates were about 10-fold smaller and unaffected by basolateral ouabain (5 mmol · l−1) or dinitrophenol (0.5 mmol · l−1). Under symmetrical conditions (100 μmol · l−1 NH4Cl on both sides) ammonia was actively excreted against the gradient of total ammonia, which increased strongly during the
experiment and against the gradient of the partial pressure of NH3. The active excretion rate was reduced to 7% of controls by basolateral dinitrophenol (0.5 mmol · l−1), to 44% by basolateral ouabain (5 mmol · l−1), to 46% by Na+-free conditions and to 42% by basolateral Cs+ (10 mmol · l−1), indicating basolateral membrane transport of NH4
+ via the Na+/K+-ATPase and K+-channels and a second active, apically located, Na+ independent transport mechanism of NH4
+. Anterior gills, which are less capable of active ion uptake than posterior gills, exhibited even increased rates of active
excretion of ammonia. We conclude that, under physiological conditions, branchial excretion of ammonia is a directed process
with a high degree of effectiveness. It even allows active extrusion against an inwardly directed gradient, if necessary.
Accepted: 11 March 1998 相似文献
10.
D. Weihrauch W. Becker U. Postel S. Luck-Kopp D. Siebers 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1999,169(1):25-37
Isolated perfused gills of stenohaline crabs Cancer pagurus adapted to seawater, brackish water-adapted euryhaline shore crabs Carcinus maenas and freshwater-adapted extremely euryhaline Chinese crabs Eriocheir sinensis were tested for their capacity to excrete ammonia. Gills were perfused with haemolymph-like salines and bathed with salines
equal in adaptation osmolality. Applying 100 μmol · l−1 NH4Cl in the perfusion saline and concentrations of NH4Cl in the bath that were stepwise increased from 0 to 4000 μmol · l−1 allowed us to measure transbranchial fluxes of ammonia along an outwardly as well as various inwardly directed gradients.
The gills of all three crab species were capable – to different extents – of active excretion of ammonia against an inwardly
directed gradient. Of the three crab species, the gills of Cancer pagurus revealed the highest capacity for active excretion of ammonia, being able to excrete it from the haemolymph (100 μmol · l−1 NH+
4) through the gill epithelium against ambient concentrations of up to 800 μmol · l−1, i.e. against an eightfold gradient. Carcinus maenas and E. sinensis were able to actively excrete ammonia against approximately fourfold gradients. Within the three crab species, the gills
of E. sinensis exhibited the greatest capacity to resist influx at very high external concentrations of up to 4000 μmol · l−1. We consider the observed capacities for excretion of ammonia against the gradient as ecologically meaningful. These benthic
crustaceans protect themselves by burying themselves in the sediment, where, in contrast to the water column, concentrations
of ammonia have previously been reported that greatly increase haemolymph levels. Electrophysiological results indicate that
the permeabilities of the gill epithelia are a clue to understanding the species-specific differences in active excretion
of ammonia. During the invasion of brackish water and freshwater, the permeabilities of the body surfaces greatly decreased.
The gills of marine Cancer pagurus exibited the greatest permeability (ca. 250 mS cm−2), thus representing practically no influx barrier for ions including NH+
4. We therefore assume that C. pagurus had to develop the strongest mechanism of active excretion of ammonia to counteract influx. On the other hand, freshwater-adapted
E. sinensis exhibited the lowest ion permeability (ca. 4 mS cm−2) which may reduce passive NH+
4 influxes at high ambient levels.
Accepted: 14 October 1998 相似文献
11.
M. Schnuch H. Seebauer 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1998,182(6):767-775
Receptor cell responses in the largest labellar (LL) and tarsal (D) taste hairs of the housefly Musca domestica were investigated electrophysiologically using the tip-recording technique. In LL hairs, test series with lactose in concentrations
of 12.5–400 mmol · l−1 yielded a threshold concentration around 12 mmol · l−1 and a calculated concentration eliciting half-maximal response of around 40 mmol · l−1, the maximal response varying between 18 and 30 impulses/300 ms. D hairs are more sensitive towards lactose, indicated by
a slightly lower threshold and a by 60% higher response to 400 mmol · l−1 lactose. The high variation in the relative stimulating effectiveness of lactose and sucrose and experiments with sugar mixtures
imply that these sugars bind to different receptor sites without noticeable cross affinity. A comparison of the concentration
response characteristics for sucrose and lactose in LL and D hairs suggests that sucrose can combine with more than one site
type, expressed in different proportions in both hair types. Results obtained with p-nitrophenyl-β-galactoside as stimulus indicate that a β-galactoside link is not sufficient for a substance to interact specifically
with the lactose binding site. The exceptional lactose sensitivity of the sugar cell in M. domestica is discussed in the context of food acquirement and digestion.
Accepted: 14 November 1997 相似文献
12.
Nigel J. Adams Berry Pinshow Leonard Z. Gannes 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(6):444-450
We used tritium-labeled water to measure total body water, water influx (which approximated oxidative water production) and
water efflux in free-flying tippler pigeons (Columba livia) during flights that lasted on average 4.2 h. At experimental air temperatures ranging from 18 to 27 °C, mean water efflux
by evaporation and excretion [6.3 ± 1.3 (SD) ml · h−1, n = 14] exceeded water influx from oxidative water and inspired air (1.4 ± 0.7 ml · h−1, n = 14), and the birds dehydrated at 4.9 ± 0.9 ml · h−1. This was not significantly different from gravimetrically measured mass loss of 6.2 ± 2.1 g · h−1 (t = 1.902, n = 14, P>0.05). This flight-induced dehydration resulted in an increase in plasma osmolality of 4.3 ± 3.0 mosmol · kg−1 · h−1 during flights of 3–4 h. At 27 °C, the increase in plasma osmolality above pre-flight levels (ΔP
osm = 7.6±4.29 mosmol · kg−1 · h−1, n = 6) was significantly higher than that at 18 °C (ΔP
osm = 0.83±2.23 mosmol · kg−1 · h−1, (t = 3.43, n = 6, P < 0.05). Post-flight haematocrit values were on average 1.1% lower than pre-flight levels, suggesting plasma expansion. Water
efflux values during free flight were within 9% of those in the one published field study (Gessaman et al. 1991), and within
the range of values for net water loss determined from mass balance during wind tunnel experiments (Biesel and Nachtigall
1987). Our net water loss rates were substantially higher than those estimated by a simulation model (Carmi et al. 1992) suggesting
some re-evaluation of the model assumptions is required.
Accepted: 8 April 1997 相似文献
13.
L. J. Schep I. G. Tucker G. Young A. G. Butt 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(5):370-377
The objective of this study was to assess regional variations in the permeability of the salmon posterior intestine and to
evaluate the effect of permeability enhancers as a basis for oral delivery of biologically active peptides. Proximal and distal
portions of the posterior intestine of the chinook salmon (Oncorhynchus tshawytscha) were removed, mounted as flat sheets in Ussing chambers and superfused with trout Ringer's. Intestinal permeability was
assessed under short-circuit conditions by measurement of 14C-mannitol (mucosal to serosal) flux. Tissues were treated either with the mucolytic agent dithiothreitol (10 mmol · l−1), the permeability enhancer sodium deoxycholate (5.0 mmol · l−1) or both and compared to untreated controls. Both proximal and distal control tissues had low permeabilities, but the distal
region had a lower transepithelial electrical resistance and produced significantly less mucus. Treatment with either dithiothreitol
or sodium deoxycholate alone reduced mucus adhering to tissue in both regions but did not increase permeability or change
transepithelial electrical resistance. In the distal region, sequential treatment with both agents significantly reduced adhering
mucus, decreased transepithelial electrical resistance, and increased tissue permeability. The salmon posterior intestine
can be divided into proximal and distal regions. The distal region is more likely to have the necessary permeability and responsiveness
to enhancement for the successful delivery of peptides or polar drugs.
Accepted: 14 January 1997 相似文献
14.
Isoflurane blocks glutamatergic excitatory transmission pre- and postsynaptically in crayfish muscle
M. Schramm J. Dudel 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1998,183(2):237-246
Crayfish neuromuscular junctions are good models for the α-amino-hydroxy-5-methyl-4-isoxazol-propionic acid-type of vertebrate
brain excitatory synapses. The action of a typical volatile anaesthetic, isoflurane, was studied on the excitatory postsynaptic
currents recorded with a perfused macropatch electrode. Isoflurane reduced quantal exitatory postsynaptic currents in amplitude,
in their rise time and in the decay time constant. Small such effects were elicited by <1 mmol · l−1 isoflurane, while the maximal isoflurane concentration of 7 mmol · l−1 reduced the amplitude to about a quarter and shortened the decay time constant even more, while the rise time was diminished
by about a quarter. This combination of effects is typical for an open channel block for which an approximate binding rate
constant of isoflurane of 6 · 105 mol−1l · s−1 and an unbinding rate of 10–100 s−1 is derived. In addition to this postsynaptic effect, isoflurane inhibited the release of transmitter quanta from the terminal,
for instance with 2.5 mmol · l−1 isoflurane by a factor of 7.3 ± 6.3 (SD). In the glutamatergic nerve terminals release is modulated by low glutamate concentrations
via a metabotropic autoreceptor which is blocked by the combination of 6-cyano-7-nitro-quinoxaline-2,3-dione and dl-2-amino-5-phosphor-valeric acid. This blocker combination also can prevent the inhibition of release by isoflurane, and it
may be suggested that isoflurane elicits inhibition of release through the metabotropic presynaptic glutamate receptors.
Accepted: 29 March 1998 相似文献
15.
Juan Fuentes F. B. Eddy 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(6):438-443
Drinking in Atlantic salmon (Salmo salar) juveniles was investigated in fresh water and following transfer to sea water. There was a significant effect of fish size
on drinking, and smolts (20–30 g) imbibed about ten times less water than alevins of 0.2–0.3 g. Freshwater smolts drank at
a rate of 0.15 ± 0.03 ml · kg−1 · h−1 and administration of doses of 10 or 20 mg · kg−1 of papaverine (stimulator of the renin- angiotensin system RAS) or [Asn1, Val5]-Angiotensin II (0.4 μmol · kg−1) resulted in significant increases in drinking, while administration of the angiotensin converting enzyme inhibitor, enalapril
(50 mg · kg−1) had no effect on drinking. Transfer of Atlantic salmon smolts to 1/3, 2/3 and full strength sea water resulted in significant
increases in drinking to 1.06 ± 0.12, 1.24 ± 0.0.16 and 3.89 ± 0.28 ml · kg−1 · h−1, respectively. In sea water, stimulation of the endogenous RAS by administration of papaverine (20 mg · kg−1) resulted in a 20% increase in drinking, while administration of enalapril to doses of 50 and 200 mg · kg−1 lowered drinking to 1.99 ± 0.48 and 0.32 ± 0.06 ml · kg−1 · h−1, respectively. All treatments were without effect on blood plasma levels of Na+ and Cl− in fresh water, while in sea water smolts both stimulation and inhibition of drinking resulted in hemoconcentration of Na+ and Cl−. The role of the renin angiotensin system in control of drinking and hydromineral balance in Atlantic salmon is discussed.
Accepted: 27 February 1997 相似文献
16.
Theodore J. Angelopoulos Robert J. Robertson F. L. Goss Allan Utter 《European journal of applied physiology and occupational physiology》1997,75(2):132-135
Eight fit men [maximum oxygen consumption (O2max) 64.6 (1.9) ml · kg−1 · min−1, aged 28.3 (1.7) years (SE in parentheses) were studied during two treadmill exercise trials to determine the effect of endogenous
opioids on insulin and glucagon immunoreactivity during intense exercise (80% O2max). A double-blind experimental design was used with subjects undertaking the two exercise trials in counterbalanced order.
Exercise trials were 20 min in duration and were conducted 7 days apart. One exercise trial was undertaken following administration
of naloxone (N; 1.2 mg; 3 ml) and the other after receiving a placebo (P; 0.9% NaCl saline; 3 ml). Prior to each experimental
trial a flexible catheter was placed into an antecubital vein and baseline blood samples were collected. Immediately after,
each subject received either a N or P bolus injection. Blood samples were also collected after 20 min of continuous exercise
(running). Glucagon was higher (P < 0.05), while insulin was lower (P < 0.05), during exercise compared with pre-exercise values in both trials. However, glucagon was higher (P < 0.05) in the P than in the N exercise trial [141.4 (8.3) ng · l−1 vs 127.2 (7.6) ng · l−1]. There were no differences in insulin during exercise between the P and N trials [50.2 (4.3) pmol · l−1 vs 43.8 (5) pmol · l−1]. These data suggest that endogenous opioids may augment the glucagon response during intense exercise.
Accepted: 15 June 1996 相似文献
17.
J. P. Danaceau M. T. Lucero 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2000,186(1):57-67
We used nystatin-patch techniques to characterize the responses of squid olfactory receptor neurons to the attractive odorant,
L-glutamate, and to study mixture interactions between glutamate and the aversive odorant, betaine. We report that glutamate
activates a cation-selective conductance that is permeable to Ca2+, K+, and Na+ and which would depolarize squid olfactory receptor neurons under physiological conditions. The responses to glutamate were
concentration dependent. The EC50 of individual cells ranged from 0.3 mmol · l−1 to 85.0 mmol · l−1. We found that individual cells were capable of responding to both glutamate and betaine, and that the relative magnitudes
of these responses varied from cell to cell. Finally, we report that current responses to binary mixtures of glutamate and
betaine are suppressed relative to the sum of the responses to the individual odors in single squid olfactory receptor neurons.
Accepted: 20 October 1999 相似文献
18.
Takayoshi Yoshida Hiroshi Watari 《European journal of applied physiology and occupational physiology》1997,75(3):200-205
To assess muscle metabolism and inorganic phosphate (Pi) peak splitting during exercise, 31-phosphorus nuclear magnetic resonance spectroscopy was performed during ramp incremental
and submaximal step exercise with and without circulatory occlusion. Seven healthy men performed calf flexion in a superconducting
magnet. There was no Pi splitting during ramp incremental exercise with the circulation present and phosphocreatine (PCr) decreased linearly by 0.07
(SEM 0.01) mmol · l−1 · s−1, while exercise with the circulation occluded caused the Pi peak to split into a high and a low pH peak. The rate of PCr decrease during exercise with the circulation occluded was 0.15
(SEM 0.03) mmol · l−1 · s−1 which with the efficiency of the adenosine 5′-triphosphate (ATP) hydrolysis reaction corresponded well to the mechanical
energy. Both with and without occlusion of the circulation PCr decreased with some time lag which may reflect the consumption
of residual oxygen. In submaximal step exercise PCr decreased exponentially at the onset of exercise with the circulation
open whereas it decreased linearly by 0.15␣mmol · l−1 · s−1 when the circulation was occluded. After exercise, occlusion of the circulation was maintained for 1 min more and there was
no PCr resynthesis. It is suggested that ATP synthesis was limited by the availability of oxygen.
Accepted: 14 August 1996 相似文献
19.
Schröder B Vössing S Breves G 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1999,169(7):487-494
From various in vivo and in vitro studies it has been shown that the rumen represents a significant site of Ca2+ absorption in sheep and goats. It was the aim of the present study to further characterize the underlying mechanisms. Unidirectional
flux rates of Ca2+ across rumen wall epithelia of sheep were measured in vitro by applying the Ussing-chamber technique in the absence of electrochemical
gradients. Under these conditions, significant Ca2+ net flux rates (Jnet) clearly indicate the presence of active mechanisms for Ca2+ transport. Short chain fatty acids (SCFAs) caused highest stimulation of Ca2+ Jnet (6.3 ± 1.9 nmol · cm−2 · h−1) when used as a mixture of acetate, proprionate and butyrate in physiological proportions (36, 15, 9 mmol · l−1, respectively). The effect of 30 mmol · l−1 butyrate (3.2 ± 0.6 nmol · cm−2 · h−1) was higher than respective amounts of propionate and acetate (0.6 ± 0.8 nmol · cm−2 · h−1 and 0.9 ± 0.8 nmol · cm−2 · h−1, respectively). Eliminating SCFAs resulted in Ca2+ Jnet of 0.4 ± 1.1 nmol . cm−2 . h−1. Addition of Ca channel blocker verapamil (mucosal 1 mmol · l−1) had no significant effect on SCFA-stimulated Jnet of Ca2+, whereas application of Na+/H+ inhibitor amiloride (mucosal 1 mmol · l−1) further enhanced the Ca2+ Jnet by >65%. The Ca2+-pump inhibitor vanadate had no significant effect on Jnet of Ca2+. Dietary Ca depletion enhanced calcitriol plasma concentrations but had no effect on active Ca2+ absorption across the rumen wall of sheep. In addition, no effect on active Ca2+ absorption could be observed during early lactation. In conclusion, there is clear evidence for the rumen as a main site
for active Ca2+ absorption in sheep. Our results suggest the presence of a Ca2+/H+ exchange mechanism in the apical membrane of rumen epithelial cells which depends on SCFA absorption and which does not seem
to be under the control of calcitriol. Basolateral Ca2+ extrusion occurs independently from Ca2+-pump activity and may be accomplished via Na+/Ca2+ exchange.
Accepted: 29 June 1999 相似文献
20.
Savvas P. Tokmakidis Luc A. Léger Theophilos C. Pilianidis 《European journal of applied physiology and occupational physiology》1998,77(4):333-342
The purpose of this study was to compare various methods and criteria used to identify the anaerobic threshold (AT), and
to correlate the AT obtained with each other and with running performance. Furthermore, a number of additional points throughout
the entire range of lactate concentrations [La−] were obtained and correlated with performance. A group of 19 runners [mean age 33.7 (SD 9.6) years, height 173 (SD 6.3)
cm, body mass 68.3 (SD 5.4) kg, maximal O2 uptake (V˙O2
max
) 55.2 (SD 5.9) ml · kg−1 · min−1] performed a maximal multistage treadmill test (1 km · h−1 every 3.5 min) with blood sampling at the end of each stage while running. All AT points selected (visual [La−], 4 mmol · l−1 [La−], 1 mmol · l−1 above baseline, log-log breakpoint, and 45° tangent to the exponential regression) were highly correlated one with another
and with performance (r > 0.90) even when there were many differences among the AT (P < 0.05). The additional points (ranging from 3 to 8 mmol · l−1 [La−], 1 to 6 mmol · l−1 [La−] above the baseline, and 30 to 70° tangent to the exponential curve of [La−]) were also highly correlated with performance (r > 0.90). These results failed to demonstrate a distinct AT because many points of the curve provided similar information.
Intercorrelations and correlations between AT and performance were, however, reduced when AT were expressed as the percentage
of maximal treadmill speed obtained at AT or percentage of V˙O2
max
. This would indicate that different attributes of aerobic performance (i.e. maximal aerobic power, running economy and endurance)
are measured when manipulating units. Thus, coaches should be aware of these results when they prescribe an intensity for
training and concentrate more on the physiological consequences of a chosen [La−] rather than on a “threshold”.
Accepted: 22 October 1997 相似文献