首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
1.  Transepithelial potential differences (PDte) and acidification rates of the bath chamber were measured on isolated perfused posterior gills of the fiddler crabUca tangeri adapted to dilute seawater.
2.  The PDte decreased to almost zero when Na+ was substituted by choline or when ouabain was added to the perfusion saline in high concentrations (10 mmol·l–1). Thus, the rheogenic NaCl-transport across the gill epithelium seems to be totally Na+-dependent.
3.  When Cl– was replaced by gluconate, a bath positive PDte occurred which was insensitive to ouabain. This PDte could also be observed when, in addition to Cl– removal, Na+ was replaced by TMA+.
4.  Bath acidification under normal conditions could be abolished by ouabain, indicating that there is H+ excretion via electrically silent Na+/H+ exchange. In contrast, bath acidification under Cl–-free conditions is only partially blocked by ouabain.
5.  It is concluded that under Cl–-free conditions a rheogenic H+-pump in the apical membrane is responsible for the ouabain-insensitive bath acidification as well as for the PDte.
Parts of this study had been published earlier in abstract form  相似文献   

2.
1.  Physiological adaptation to hypothermia were studied in newly hatched great snipe chicks (Gallinago media) by measuring oxygen uptake (VO2), heart rate (HR), respiratory frequency (RF), and body temperature (Tb) at different ambient temperatures (Ta).
2.  Tb of 1-day-old chicks at Ta of 35°C stabilized at about 40°C. At Ta between 20 and 30°C the chicks maintained a Tb about 8°C above Ta. Hatchlings maintained a higher gradient when active than when resting. Below 20°C they were unable to maintain a stable Tb.
3.  In resting hatchlings VO2 was similar at Ta between 35 and 20°C (Tb 40–30°C), VO2 range 1.7–2.5 ml·g-1·h-1. Below 20°C, VO2 declined with time.
4.  The HR of 1-day-old chicks fell linearly with Tb during cooling. The Q10 of the HR was 1.7 at Tb 38°C and increased to 3.0 at 29°C. The RF showed a slight tendency to decrease with decreasing Tb.
5.  It is concluded that the ability to maintain normal dexterity at low Tb is an important aspect of snipe survival strategy. Maintaining a temperature gradient rather than a constant high Tb presumably saves energy. It is suggested that the mechanisms whereby VO2 is maintained at a low Tb may involve isoenzymes and adaptations of the nervous system. However, such adaptations would not seem to affect the pacemaker mechanism as evidenced by the high Q10 of the HR.
  相似文献   

3.
1.  We investigated potassium (K) transport in vitro across four major segments of the avian intestine. In normal fed birds, the most proximal segment, the duodenum, had very low unidirectional rates of K transport (Jms 6.7 nEq·cm–2·hr–1; Jsm 7.7 nEq·cm–2·hr–1). The jejunum had the greatest unidirectional K flux of the segments studied (Jms 36.6 and Jsm 85.5 nEq·cm–2·hr–1), and this segment showed a net K secretion (48.9 nEq·cm–2·hr–1). The ileum had a significantly lower Jms (16.5 nEq·cm–2·hr–1) than did the jejunum, and this segment also showed a net K secretion (28 nEq·cm–2·hr–1). Potassium transport across the mucosal surface of the colon was very low (Jms 7.7 nEq·cm–2·hr–1) while the Jsm flux was relatively large, giving a net K secretion of 45.7 nEq·cm–2·hr–1.
2.  When tissues were bathed in solutions having approximately normal in vivo K concentrations on both sides of the membranes and open circuit PD (to simulate in vivo conditions), the jejunum was the only segment that showed a net K absorption (83 nEq·cm–2·hr–1).
3.  When birds were fed a low K diet for 2 weeks, the colon showed the greatest response with Jms for K increasing 12 fold over control.
4.  From these studies we conclude that in normal birds the duodenum appears to be relatively impermeable to K and does not appear to play a significant role in K transport. However, the jejunum by virtue of its relatively greater permeability to K, the total length of jejunum comprising the intestine (66%), and the in vivo K gradients, seems to be most important in K absorption in the normal bird. The ileum and colon were major sites of K secretion in vitro and appear to be most important in intestinal regulation of K transport in response to changes in the dietary K load.
  相似文献   

4.
1.  In this commentary we discuss results obtained by a micromethod for the study of Cl– permeability across single nerve membranes from rabbit Deiters' neurons.
2.  These results showed the presence of GABAA receptors on the nerve cell membrane cytoplasmic side.
3.  We could show that these receptor complexes have a higher affinity for GABA than their extracellularly facing counterparts. Moreover, they present a phenomenon of desensitization. Another distinct property is that upon activation by GABA, they expose positive charges at their cytoplasmic mouths.
4.  We propose that these receptor complexes could functionin situ as a device for extruding Cl– anions from the nerve cell interior. This phenomenon would create an electrochemical gradient for Cl– penetration into the cell upon the action of extracellular GABA, after its presynaptic release.
  相似文献   

5.
1.  Oxygen uptake, carbon dioxide release, water release and heart frequency were studied in the tarantula,Eurypelma californicum. Oxygen uptake also was studied in the scorpion,Pandinus imperator.
2.  Basal metabolic rate, oxygen uptake of animals at rest as measured bymanometric respirometry, was very low in both species [mostly well below 1 ml O2 (STPD)·h–1]. Its relation to body mass and temperature was examined. A respiratory quotient of 0.71 inEurypelma at rest indicates oxidation of fat.
3.  To assess short-term changes and maximum rates, gas exchange at the four book lungs and heart frequency were simultaneously measured inEurypelma by using respiratory masks andflowthrough respirometry.
4.  During maximum activity, and were often reduced. During rest and in a later phase of recovery, slow fluctuations in oxygen uptake, carbon dioxide and water release occurred. These are probably caused by fluctuations in heart frequency.
5.  After 1 min of maximum activity, on average, increased to a maximum of 81 l (STPD)·min–1, to 50 l (STPD)·min–1, and heart frequency to 75 beats·min–1. Typical values for pulmonary water release were 50 (at rest) and 100–120 (maximum) g H2O·min–1.
6.  During recovery, and heart frequency changed faster than , causing changes in the respiratory quotient. It initially dropped, then increased and finally returned to the original value.
7.  A plot of heart frequency vs during recovery revealed a linear relationship between both variables.
This and the following two papers are dedicated to the memory of Prof. Bernt Linzen, who promoted our work by his continuous support and the creation of an extraordinarily encouraging work atmosphere. R.P., T.F.  相似文献   

6.
This study evaluated the impact of P supply on rice plant development and the methane budget of rice fields by 2 different approaches: (1) root growth, exudation and aerenchyma formation were recorded in an experiment with hydroponic solution; (2) dissolved CH4 concentration and CH4 emission were investigated in a pot experiment. In both approaches, we used three different cultivars and three levels of P supply. In the experiment with solution culture (0.5 ppm, 5 ppm, and 10 ppm P), root exudation ranged between 0.5 to 36.7 mol C plant–1 h–1 and increased steadily with plant growth at given P level. Low P supply resulted in
•  depressed shoot growth but increased root growth in culture solution
•  increments in the root/shoot ratio by factors of 1.4 to 1.9 at flowering stage
•  enhanced the development of root aerenchyma, and
•  stimulation of root exudation per plant by factors of 1.3–1.8 as compared to medium P
•  supply and by factors of 2.1–2.4 as compared to high P supply.
However, root exudation did not differ among treatments when related to the dry weight of roots. Thus, high exudation rates were caused by larger root biomass and not by higher activity of the root tissue.The pot experiment was conducted with a P-deficient soil that was either left without amendment or fertilized by 25 and 50 mg P kg soil –1 , respectively. Low P supply resulted in
•  higher CH4 concentrations in soil solution; i.e., at flowering stage the soil solution concentrations were 34–50 M under P deficiency and 10–22 M under ample P supply and · significant increases of CH4 emission rates during the later stages of plant growth.
•  These findings reflect a chain of response mechanisms to P stress, that ultimately lead to higher methane emission rates.
  相似文献   

7.
1.  Heat transfer was evaluated in isolated-perfused second gill arches and in isolated-perfused heads of rainbow trout.
2.  At a perfusion flow of 0.5 ml min–1 the second gill arch exchanges 0.774±0.024 ( [`(X)]\bar X ±SE,n=6) cal min–1°C–1. This value can be increased by 11% with the infusion of 10–5 M epinephrine.
3.  With perfusion flows of 16 and 20 ml min–1, isolated-perfused heads had a transfer maximum (hAmax) of 21.27±0.57 (21) and 24.79±0.77 (21) cal min–1 °C–1 and a ventilatory flow ( [(V)\dot]\dot V g) resulting in 0.5hAmax transfer ( [(V)\dot]\dot V 0.5 max) of 144±17 (21) and 183±23 (21) ml min–1 respectively.
4.  The values of [(V)\dot]\dot V 0.5 max were unaffected by the administration of 10–5 M epinephrine, 10–8 M or 10–7 M acetylcholine.hAmax was increased only in the presence of 10–5 M epinephrine.
5.  Increasing perfusion flow increasedhAmax without affecting [(V)\dot]\dot V 0.5 max. At a given perfusion flow there were no changes in heat transfer when heart rate and stroke volume were varied.
6.  Analysis of a simple model for whole body heat exchange indicated that the gills may account for as much as 60% of the total heat exchanged by the animal.
  相似文献   

8.
1.  Maximal oxygen consumption rates ( [(V)\dot]\textO\text2 \dot V_{{\text{O}}_{\text{2}} } max; units, ml/g·h) were determined for four species of amphibians representing four families with habitat preferences varying from aquatic to terrestrial. Measured [(V)\dot]\textO\text2 \dot V_{{\text{O}}_{\text{2}} } max were:Xenopus laevis (aquatic), 1.33±0.16;Rana pipiens (semi-terrestrial), 0.54±0.10;Bufo cognatus (terrestrial), 1.91±0.26; andScaphiopus couchii (terrestrial), 1.91±0.26.
2.  In order to assess possible cardiovascular bases for these interspecific differences, heart rate increments (differences between resting and active heart rates) and ventricle weights were measured to evaluate differential cardiac outputs. In order to assess possible differential blood oxygen capacities, hematocrits and hemoglobin concentrations were measured. Blood volumes were determined to assess total blood oxygen storage capacities.
3.  Ventricle weights were statisticaly significantly different (p<0.01) between=" all=">B. cognatus>S. couchii>X. laevis>R. pipiens. These differences were closely positively correlated with the maximal metabolic rates of the species (Fig. 3a).
4.  There were no differences in heart rate increments between the four species (Fig. 2).
5.  Blood oxygen capacities were directly correlated with hemoglobin concentrations (Fig. 1). There were no interspecific differences in the amounts of oxygen bound per gram of hemoglobin (1.3 ml O2/g Hb). Blood oxygen capacities were significantly different in the following sequence;X. laevis >S. couchii andB. cognatus>R. pipiens.
6.  X. laevis had statistically significantly greater hematocrits than did the other three species.R. pipiens had significantly lower mean corpuscular hemoglobin concentrations.
7.  Blood volumes were statistically significantly different between all species examined,S. couchii>B. cognatus>X. laevis>R. pipiens.
8.  It is suggested that greater maximal oxygen consumption rates in anurans are correlated with 1) increased cardiac outputs based upon increased stroke volumes, 2) increased blood oxygen capacities due to either increased mean corpuscular hemoglobin concentration or increased hematocrit. Increased selective pressure for aerobic metabolism is also closely positively correlated with maximal blood oxygen storage capabilities.
  相似文献   

9.
1.  Rates of oxygen consumption were measured during locomotion in five species of marsupials of the family Dasyuridae. The body weights of the animals ranged between 0.15 and 1.12 kilograms.
2.  The rate of change of power input with speed was generally lower than equivalent eutherian values. The extrapolation to zero speed was consistently a higher multiple of resting metabolic levels than found in eutherians.
3.  The minimum cost of locomotion (M run) as a function of body mass (wt) is described by the equationM run=4.75 wt–0.34. The exponent is similar to that described for eutherians and reptiles, but the constant term is significantly lower.
4.  Metabolic scope in these animals is similar over the size range used and may be greater than in eutherians.
5.  Heat dissipation during locomotion has been partitioned into evaporative and non-evaporative routes. Storage of heat during locomotion was never more than fifty per cent of total production.
  相似文献   

10.
1.  The diffusive hydrogen conductance of chicken eggshell compound membrane was measured in situ on day 16 of incubation, in a direction parallel to the shell and the chorioallantois (lateral conductance). A value of 3.9 mmol d–1 kPa–1 was obtained through a ring 13.29 cm in circumference, 0.0076 cm thick and 0.3 cm long.
2.  Lateral hydrogen conductance for 1 mm2 of shell membrane 76 m thick is 30 times the conductance of one pore serving the same area.
3.  Lateral conductance for H2 is not significantly influenced by chorioallantoic perfusion.
4.  Oxygen consumption change due to partial covering of the hen eggshell indicates that there is a significant resistance to lateral diffusion of oxygen under the shell toward the covered area.
  相似文献   

11.
1.  The action of melatonin was investigated in a colonial anthozoan, the sea pansy Renilla koellikeri, in which rhythmic contractions underlying peristalsis were previously shown to be potentiated by serotonin (5-HT) and cAMP analogues (Anctil 1989).
2.  Melatonin (2–1000 mol·1-1) consistently and reversibly depressed the amplitude of rhythmic contractions, the latter all but vanishing at the most effective concentration (10 mol·1-1). In addition, the frequency of rhythmic contractions incurred a 25% reduction in some preparations exposed to melatonin (10–20 mol·1-1). Vaseline gap experiments showed that this response was restricted to tissues directly exposed to melatonin.
3.  The potentiating effect of 5-HT on rhythmic contractions was eliminated in a reversible manner in the presence of melatonin. The latter also caused a 50% reduction of the amplitude of contractions elicited by field electrical stimulation.
4.  Dibutyryl or 8-bromo cGMP, as well as the phosphodiesterase inhibitor IBMX, mimicked the melatonin-induced response and the effects of melatonin on the 5-HT potentiation or contractile response to electrical stimulation. cGMP levels, measured by radio-immunoassay (RIA) in rachidial tissues, increased 3-fold above basal levels in the presence of melatonin (0.01 mmol·1-1) and 2-fold with IBMX (1 mmol·1-1). In contrast, RIA measurements of cAMP levels showed the latter to fall to 50 and 40% of control values in the presence of melatonin (0.01 mmol·1-1) and IBMX (0.1 mmol·1-1), respectively. These results and other findings suggest that a cGMP-mediated melatonergic mechanism participates in an antagonistic fashion with 5-HT in the modulation of rhythmic contractions and peristalsis of the sea pansy.
  相似文献   

12.
1.  The reactions of tympanic nerve fibers ofLocusta migratoria were recorded by glass microelectrodes in the metathoracic ganglion.
2.  The units were classified by frequency-, intensity-, and directional characteristics as well as by their response pattern. The response to speciesspecific song is compared with the response to song ofEphippiger ephippiger.
3.  The physiological properties lead to a classification into three types of low-frequency neurons (characteristic frequency 3.5–4 kHz; 4kHz; 5.5–6 kHz) and one type of high-frequency neuron (12–20 kHz). This is similar to other species (Gray, 1960, Michelsen, 1971).
4.  Intensity-coding is done by sharp rising intensity characteristics and by different absolute thresholds of the units.
5.  There is a marked directional sensitivity with some differences between LF and HF units. In the low frequency range the tympanal organ seems to react as a pressure gradient receiver; for high frequencies another mechanism is discussed.
6.  No filtering of species-specific song takes place at the level of the receptor cells.
  相似文献   

13.
1.  At ambient temperatures (T a) between 39 and 43°C, specimens of the waterproof treefrogChiromantis xerampelina, resting quietly in wind tunnels, adjust rates of evaporative water loss (EWL), maintaining body temperature (T b) 2–4°C belowT a.
2.  Brain heating and cooling, respectively, increased and decreased steady-state rates of thermoregulatory evaporative water loss (EWL), driving negative feedback changes inT b.
3.  Continuous infusions of epinephrine resulted in specific, dose-dependent, saturable increases in EWL; isoproterenol was more potent than epinephrine, which was more potent than phenylephrine. Tyramine injection also stimulated EWL.
4.  Non-specific increases in EWL stimulated by injections of cholinergic agonists were weakly antagonized by atropine, but thermally induced EWL, as well as adrenergically and cholinergically stimulated increases in EWL, were abolished by beta-adrenergic antagonists.
5.  Sweating decreased andT b increased during ganglionic blockade.
6.  The observations suggest thatC. xerampelina controls thermoregulatory EWL by modulating the sympathetic nervous outflow stimulating beta-adrenergic receptors on cutaneous mucous glands.
  相似文献   

14.
3DFS is a 3D flexible searching system for lead discovery. Version 1.0 of 3DFS was published recently (Wang, T.; Zhou, J. J. Chem. Inf. Comput. Sci., 1998, 38, 71–77). Here version 1.2 represents a substantial improvement over version 1.0. There are six major changes in version 1.2 compared to version 1.0.
1.  A new rule of aromatic ring recognition.
2.  The inclusion of multiple-type atoms and chains in queries.
3.  The inclusion of more spatial constraints, especially the directions of lone pairs.
4.  The improvement of the query file format.
5.  The addition of genetic search for flexible search.
6.  An output option for generating MOLfiles of hits.
Besides the above, this paper supplies:
1.  More query examples.
2.  A comparison between genetic search and Powell optimization.
3.  More detailed comparison between 3DFS and Chem-X.
4.  A preliminary application of 3DFS to K+ channel opener studies.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1007/s0089490050231  相似文献   

15.
1.  Coupling mechanisms between ciliary beating and the membrane potential in Paramecium were investigated under voltage clamp applying intracellular pressure injection of cAMP, cGMP and Ca-EGTA buffer. Ciliary responses following step changes in membrane potential were recorded by high-speed video on magnetic tape.
2.  Injections of cAMP and cGMP up to millimolar concentrations caused no detectable changes in the frequency voltage relationship. A minor effect was that the ciliary reorientation towards the anterior cell end (reversal) tended to be inhibited with depolarization up to 10 mV.
3.  Injection of Ca2+ into the cell clamped at the resting potential caused a transient anteriad ciliary reorientation and a simultaneous increase in the beating frequency.
4.  Injection of EGTA (to buffer Ca2+ below 10–8 M) was ineffective in relation to frequency for several minutes. After this time, hyperpolarization- and depolarization activated frequency responses of EGTA-injected cells were increasingly inhibited. The ciliary reorientation following depolarization was not affected by EGTA.
5.  A posterior contraction of the cell diameter was noticed upon membrane hyperpolarization. The contraction coincided in time with the increase in beating frequency.
6.  The results support the view that the voltage-dependent augmentation of the ciliary beating rate is not directly mediated by an intracellular increase in either cAMP or cGMP.
7.  The role of Ca2+ as intracellular messenger in the ciliary and somatic compartments is discussed.
  相似文献   

16.
1.  Chronic ingestion of caffeine by male NIH strain mice alters the density of a variety of central receptors.
2.  The density of cortical A1 adenosine receptors is increased by 20%, while the density of striatal A2A adenosine receptors is unaltered.
3.  The densities of cortical 1 and cerebellar 2 adrenergic receptors are reduced byca. 25%, while the densities of cortical 1 and 2 adrenergic receptors are not significantly altered. Densities of striatal D1 and D2 dopaminergic receptors are unaltered. The densities of cortical 5 HT1 and 5 HT2 serotonergic receptors are increased by 26–30%. Densities of cortical muscarinic and nicotinic receptors are increased by 40–50%. The density of cortical benzodiazepine-binding sites associated with GABAA receptors is increased by 65%, and the affinity appears slightly decreased. The density of cortical MK-801 sites associated with NMDA-glutaminergic receptors appear unaltered.
4.  The density of cortical nitrendipine-binding sites associated with calcium channels is increased by 18%.
5.  The results indicate that chronic ingestion of caffeine equivalent to about 100 mg/kg/day in mice causes a wide range of biochemical alterations in the central nervous system.
  相似文献   

17.
1.  In a concentration-dependent manner neuropeptide Y was found to be a potent inhibitor of the spontaneous activation of human granulocytes and macrophages as well asMytilus edulis immunocytes.
2.  Neuropeptide Y also inhibited the chemotaxic response of these immunocytes to the chemoattractant f-MLP.
3.  Incubation of both the human and the invertebrate immunocytes in f-MLP (10–9 M) causes activation as noted by random locomotion (chemokinesis). Neuropeptide Y also blocked f-MLP-induced chemokinesis.
4.  The results suggest that neuropeptide Y may, in addition to other functions, serve as an endogenous regulator of immunocyte function.
  相似文献   

18.
1.  Properties of the membrane currents ofDidinium nasutum have been investigated under voltage clamp in different solutions and after deciliation.
2.  Theearly transient Ca2+ inward current activates in a voltage-dependent manner. Inactivation is both Ca2+ -dependent and voltage-dependent.
3.  Alate Ca2+ current rises with time to peak > 50 ms and decays in the order of seconds.
4.  Activation and inactivation of the late Ca2+ current is voltage-dependent.
5.  The delayed outward current is activated by voltage. The kinetics of this K+ current, but not its amplitude, are enhanced in the presence of intracellular EGTA.
6.  The two voltage-dependent Ca2+ channels are located in the cilia, whereas all K+ channels are restricted to the somatic membrane.
  相似文献   

19.
1.  The effect of outward and inward water flows through the membrane on outward potassium currents of dialyzedHelix pomatia neurons was studied.
2.  An outward water flow increased the peak and sustained outward potassium currents and accelerated the kinetics of their activation. An inward water flow had quite opposite effects—it decreased the peak and sustained potassium currents and delayed the kinetics of their activation.
3.  The analysis of the effect of water flow on the conductance of potassium channels showed that an outward water flow increased both the potassium conductance at a given potential (gk) and the maximum potassium conductance (g k max ). An inward water flow again had the opposite effect—it decreased the potassium conductance at given potential and the maximum potassium conductance.
4.  Neither an outward nor an inward water flow significantly affected the fraction of open potassium channels at a given potential [n (V)].
5.  These data suggest that in dialyzed neurons the changes of outward potassium current during water flow through the membrane are due mainly to the changes in single-channel conductance and the time constant of current activation.
  相似文献   

20.
We have identified a nerve carrying auditory afferents and characterized their physiological responses in the tiger beetle,Cicindela marutha.
1.  The tympana are located at the lateral margins of the first abdominal tergum. The nerve carrying the tympanal afferents is a branch of the dorsal root from the first abdominal ganglion.
2.  Both male and female auditory afferent responses are sharply tuned to 30 kHz with sensitivities of 50–55 dB SPL.
3.  The auditory afferents show little adaptation and accurately code the temporal characteristics of the stimulus with the limit of a resolution of 6–10 ms.
4.  The difference in threshold between contralateral and ipsilateral afferents for lateral stimuli is greatest at 30 kHz and is at least 10–15 dB.
5.  Ablation studies indicate that the floppy membrane in the anterolateral corner of the tympanum is crucial for transduction while the medial portion of the tympanum is less important.
6.  The tiger beetle and acridid (locust and grasshopper) ears have evolved independently from homologous peripheral structures. The neural precursor of the tympanal organs in both animals is likely the pleural chordotonal organ of the first abdominal segment.
  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号