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1.
The use of amiloride to uncouple branchial sodium and proton fluxes in the brown trout, Salmo trutta
I. D. Nelson W. T. W. Potts H. Huddart 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(2):123-128
Resting proton, ammonium and sodium fluxes in Salmo trutta were 492.6 ± 19.5 (n = 29); 122.9 ± 34.2 (n = 28) and 277.1 ± 18.5 (n = 50) μmol · kg−1 · h−1, respectively. The resting transepithelial potential was found to be composed of three successive potentials, the outermost
averaging −7.36 ± 0.19mV, the second, −14.3 ± 1.4 mV and the third −37 ± 1.7 mV. Amiloride inhibits the proton, ammonium and
sodium fluxes in a dose-dependent manner at concentrations of 0.5 mmol · 1−1 and 0.1 mmol · l−1, but at 0.01 mmol · l−1, proton and ammonium fluxes remained at control levels whilst the sodium was reduced to 70.59 ± 7.29 μmol · kg−1 · h−1. The trans-epithelial potential was effected in a bi-phasic manner by 0.5 mmol · l−1 amiloride. An initial hyperpolarisation of ca. 6 mV was followed by a sustained depolarisation of ca. 14 mV (towards zero)
which persisted until the amiloride was washed off the gill. The initial hyperpolarisation was thought to reflect a rapid
inhibition of a positive inward sodium current and the subsequent depolarisation was due to the inhibition of a positive outward
current (proton) which would abolish the transepithelial potential. However, at 0.01 mmol · l−1 only the hyperpolarisation was seen, due to the inhibition of only the inward sodium current. Acetazolamide (0.1 mmol · l−1) was found to have no significant effect on the proton, ammonium and sodium fluxes. These results indicate that the proton
and sodium fluxes across the gill of the freshwater trout are not tightly linked. While this suggests that the trout gill
resembles the model of Ehrenburg et al. (1985) of sodium uptake in frog skin, the apical potentials measured in the pavement
epithelial cell(s) are too low to account for sodium uptake unless the activity of the sodium in the cells is very low.
Accepted: 8 August 1996 相似文献
2.
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
3.
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
4.
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
5.
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
6.
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
7.
Luiz Eduardo Maia Nery Marcelo Alves da Silva Lars Josefsson Ana Maria Lauro Castrucci 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(8):570-575
The cellular system responsible for the transduction of the pigment-concentrating hormone (PCH) signal was investigated in
erythrophores of the freshwater shrimp, Macrobrachium potiuna. Dose-response curves to the hormone were determined in the absence and in the presence of several drugs that affect sequential
steps of the Ca2+-dependent signalling pathway. Additionally, the ability of forskolin to induce pigment dispersion was evaluated. Neomycin
sulphate (10−4 and 10−3 mol · l−1), trifluoperazine (10−5 and 10−4 mol · l−1), 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (10−7 and 10−5 mol · l−1) and okadaic acid (10−7 mol · l−1) significantly (P<0.05) decreased the responses to PCH. However, okadaic acid at low concentration (10−9 mol · l−1) and cyclosporin A (10−6 and 10−5 mol · l−1) did not significantly (P>0.05) affect PCH activity. Forskolin (10−4 mol · l−1) was able to half-maximally reverse the hormone-induced aggregation. Our results suggest that the pigment-concentrating hormone
induces pigment aggregation through a Ca2+-dependent pathway with a posteriori phosphatase activation, probably the serine/threonine phosphatase 1.
Accepted: 30 June 1997 相似文献
8.
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
9.
T. Kuriu F. Saitow Y. Nakaoka Y. Oosawa 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1998,183(2):135-141
The cooling of deciliated Paramecium cells induced a transient Ca current and its amplitude depended on the rate of the temperature drop. The amplitude of the
Ca current was increased by the addition of Ca2+ to the bath solution in a concentration-dependent manner, whereas Ni2+, Co2+, Mn2+ and Mg2+ each reversibly inhibited the Ca current in a concentration-dependent manner with apparent dissociation constants of 0.52,
0.66, 0.67 and 2.17 mmol · l−1, respectively. The Ca current was also inhibited reversibly by amiloride, with a dissociation constant of 0.32 mmol · l−1. The Ca current was desensitized by repetitive cooling. The amplitude of the Ca current at the second cooling was smaller
than that at the first cooling when the interval was short, but recovered as the interval increased. Replacing extracellular
Ca2+ with equimolar Sr2+ or Ba2+ did not significantly affect the amplitude of the current response to cooling, but it accelerated the rate of recovery from
desensitization and slowed the decay of the current response. These results suggest that the desensitization and the inactivation
of the Ca current may involve a Ca2+-dependent pathway.
Accepted: 8 March 1998 相似文献
10.
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
11.
A. D. Blest Sally Stowe 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1997,180(4):347-355
(1) In vitro retinas of a crab, Leptograpsus, were treated with a phospholipase inhibitor, manoalide, or a G-protein activator, Mas-7. Both drugs address early stages
of the phototransduction cascade. (2) Manoalide inhibited the light-dependent reduction of rhabdoms during the `day' phase
of the light cycle, but did not induce rhabdom overgrowth. Following a period of darkness manoalide failed to affect the diminution
of illuminated rhabdoms. (3) The diminution of rhabdoms that follows photoreceptor depolarisation induced by 100 mmol · l−1 K+ in darkness was not affected by 2␣μmol · l−1 manoalide. (4) When retinas in the `night' phase were treated with Mas-7 in darkness, rhabdom diameters were augmented, concurrently
with endocytosis of photoreceptor plasma membranes. (5) The results of combining manoalide and Mas-7 with actinomycin D, U-57908
or okadaic acid, drugs used in previous studies to manipulate steps notionally lower in the transduction cascade, lead to
a hypothetical model for the regulation of phototransductive membrane turnover by arthropods.
Accepted: 3 October 1996 相似文献
12.
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
13.
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
14.
Evidence for NO-dependent vasodilation in the trout (Oncorhynchus mykiss ) coronary system 总被引:1,自引:0,他引:1
T. Mustafa C. Agnisola J. K. Hansen 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(2):98-104
The effects of l-arginine, and its analogues N
ω-nitro-l-arginine methyl ester and N
ω-nitro-l-arginine on vascular resistance were investigated in the intact coronary system of an isolated non-working trout heart preparation.
l-Arginine, at 10–8 mol · l–1induced a slight vasodilatory effect (max 10%). N
ω-nitro-l-arginine methyl ester and N
ω-Nitro-l-arginine in the range 10–8–10–4 mol · l–1 caused dose-dependent increases in coronary resistance. The vasodilatory action of l-arginine was abolished when the preparation was pretreated with 10–4 mol · l–1
N
ω-nitro-l-arginine or N
ω-nitro-l-arginine methyl ester. Nitroprusside alone at 1 mmol · l–1 induced a maximum vasodilation (30%) of the coronary system. Methylene blue a known inhibitor of guanylate cyclase, induced
a strong vasoconstriction (already significant at 10–5 mol · l–1) and was able to overcome the vasodilative effect of nitroprusside. The endothelial nitric oxide agonists acetylcholine and
serotonin, established in mammalian vessels, also mediate vasodilation in trout coronary system. In 50% of preparations, acetylcholine
induced a biphasic response with vasodilation at low concentration (max 15% at 10–8 mol · l–1). Serotonin displayed a dose-response vasodilation in the range 10–8–10–4 mol · l–1 (max 20%). These vasodilative effects were reduced or abolished by 10–4 mol · l–1
l-NA. These data support the existence of NO-mediated vasodilation mechanisms in the trout coronary system.
Accepted: 1 July 1996 相似文献
15.
J.-J. Janvier 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(7):517-526
Prostaglandin E2 (PGE2) injection caused an initial decrease in heart rate (HR) (55%), cardiac output (QC) (55%), ventral (VAP, 40%) and dorsal
(DAP, 60%) aortic pressures, associated with a marked gill vasoconstriction (100%) and a systemic vasodilation (30%) while
cardiac stroke volume (CSV) remained unchanged. It was followed by a progressive recovery of HR, DAP, and vascular resistances
to control values while VAP, QC, and CSV significantly increased (20%, 40%, and 40%, respectively). Bradycardia was abolished
either by atropine treatment or bilateral section of the cardiac vagus, suggesting that bradycardia could be the consequence
of a vagal mechanism triggered by a central action of PGE2. The increase in QC is due to the increase in CSV, which suggests a positive inotropic action of PGE2. Infusion with PGE2 (10−9 to 10−5 mol · l−1) did not cause any significant effect on the branchial vasculature in vitro, but when the preparation was pre-treated with
adrenaline (10−8 mol · l−4), a dose-related vasoconstrictory response to PGE2 (10−9 to 10−5 mol · l−1) occurred. A significant rise (25%) in gill vascular resistance was observed in vivo after treatment with the β-blocker propranolol
(2.0 mg · kg−1), suggesting the existence of a vasodilatory β-adrenergic control of the branchial vasculature. PGE2 caused an apnea followed by a simultaneous tachypnea (50%) and decrease in ventilatory amplitude (40%). The resulting decrease
in ventilatory water flow (Qw) was accompanied by a fall in arterial O2 tension (Pa O
2). Under steady Qw in curarized eels, an initial fall in Pa O
2 was still observed during the PGE2-induced gill vasoconstriction. It is concluded that PGE2 could play a role in the regulation of gas exchanges and blood circulation in particular environmental conditions which require
an impairment of gill respiration and a redistribution of blood to the benefit of the systemic vascular bed.
Accepted: 3 June 1997 相似文献
16.
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
17.
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
18.
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
19.
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
20.
M. D. Baustian S. Q. Wang K. W. Beyenbach 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(1):61-70
Plasma and urine of toadfish (Opsanus tau) in sea water and 10% sea water were analyzed to assess responses of an aglomerular fish to hypoosmotic challenge. Following
transfer to 10% sea water, plasma osmotic pressure decreased slowly from 318 to 241 mmol · kg H2O−1, over a period of 10–15 days. Urine osmotic pressure decreased in parallel from 299 to 207 mmol · kg H2O−1, leaving urine/plasma ratios of osmotic pressure essentially unchanged. In contrast, the volume and composition of urine
changed rapidly following transfer to 10% sea water. Urine flow rate increased 110% from 3.0 to 6.3 μl · 100g−1 · h−1 and Na+ excretion increased 346%, while excretion of Mg2− and SO4
2− decreased 81% and 90%, respectively. Excretion rates for Cl− were low in seawater toadfish and decreased further in 10% sea water. An unknown sulfur-containing anion, present in the
urine of seawater toadfish, contributed significantly to the composition and ionic balance in urine of toadfish in 10% sea
water. These results suggest that the inability to produce strongly dilute urine obliges toadfish to lose salt in order to
excrete water, in hypoosmotic media. The decrease in plasma osmotic pressure may be both a strategy to reduce osmotic and
ionic gradients in dilute media and a consequence of the kidney's inability to excrete water without salt.
Accepted: 22 August 1996 相似文献