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31.
ATP-Activated Nonselective Cation Current in NG108-15 Cells 总被引:5,自引:0,他引:5
Hiromi Kaiho Junko Kimura Isao Matsuoka Tadanori Kumasaka Hironori Nakanishi 《Journal of neurochemistry》1996,67(1):398-406
Abstract: ATP (1 mM) induced a biphasic increase in intracellular Ca2+ concentration ([Ca2+]i), i.e., an initial transient increase decayed to a level of sustained increase, in NG108-15 cells. The transient increase was inhibited by a phospholipase C inhibitor, 1-[6-[[17β-3-methoxyestra-1,3,5(10)-trien-17-yl]amino]hexyl]-1H-pyrrole-2,5-dione (U73122), whereas the sustained increase was abolished by removal of external Ca2+. We examined the mechanism of the ATP-elicited sustained [Ca2+]i increase using the fura-2 fluorescent method and the whole-cell patch clamp technique. ATP (1 mM) induced a membrane current with the reversal potential of 12.5 ± 0.8 mV (n = 10) in Tyrode external solution. The EC50 of ATP was ~0.75 mM. The permeability ratio of various cations carrying this current was Na+ (defined as 1) > Li+ (0.92 ± 0.01; n = 5) > K+ (0.89 ± 0.03; n = 6) > Rb+ (0.55 ± 0.02; n = 6) > Cs+ (0.51 ± 0.01; n = 5) > Ca2+ (0.22 ± 0.03; n = 3) > N-methyl-d -glucamine (0.13 ± 0.01; n = 5), suggesting that ATP activated a nonselective cation current. The ATP-induced current was larger at lower concentrations of external Mg2+. ATP analogues that induced the current were 2-methylthio-ATP (2MeSATP), benzoylbenzoic-ATP, adenosine 5′-thiotriphosphate (ATPγS), and adenosine 5′-O-(2-thiodiphosphate), but not adenosine, ADP, α,β-methylene-ATP (AMPCPP), β,γ-methylene-ATP (AMPPCP), or UTP. Concomitant with the current data, 2MeSATP and ATPγS, but not AMPCPP or AMPPCP, increased the sustained [Ca2+]i increase. We conclude that ATP activates a class of Ca2+-permeable nonselective cation channels via the P2z receptor in NG108-15 cells. 相似文献
32.
R.L. ALEXANDER 《Zoological Journal of the Linnean Society》1996,118(2):151-164
The presence of cranial retia mirabilia in rays of the genus Mobula is well established. Although previously regarded as consisting exclusively of arteries, the presence of veins has now been established in gross dissections of the rete in the mobulid, Manta birostris. Histological examination of the retia in Manta birostris and Mobula tarapacana confirms the presence of veins. These findings suggest the presence of a counter-current heat-exchanger that warms the brain. 相似文献
33.
Zhao Rongrui Wang Wenze Wu Bowei Hoebeke Johan Hjalmarson Åke Fu Michael L. X. 《Molecular and cellular biochemistry》1996,163(1):185-193
The effects of anti-peptide antibodies against the second extracellular loop of human M2 muscarinic receptor on transmembrane potentials and currents in guinea pig single ventricular cells were analyzed using whole-cell patch clamp technique. These effects were compared with those of the muscarinic receptor agonists carbachol and acetylcholine. The antibodies shortened the action potential duration in a dose-dependent manner. By using a ramp or step rectangular pulse protocol, it was found that the antibodies increased the outward K+ current and decreased the inward basal I Ca significantly. The reversal potential of both carbachol-and antibody-induced extra currents were close to –80 mV, being in proximity to the calculated Ek of –90 mV. A -adrenergic receptor agonist, isoprenaline, prolonged the action potential and increased the overshoot which could be inhibited by both antibody and carbachol. Isoprenaline increased inward Ica and outward Ik simultaneously. Both antibody and carbachol could significantly reduce the isoprenaline-stimulated ICa but not the isoprenaline-stimulated Ik. The antibody- or carbachol-induced outward K+ current and the depressant effects of antibody and carbachol on isoprenaline-stimulated Ica were partially antagonized by atropine. These results suggest that the anti-M2 muscarinic receptor antibodies display a stimulatory activity similar to muscarinic receptor agonist on the receptor-mediated electrophysiological events. 相似文献
34.
S. Zielinski H. O. Pörtner 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1996,166(8):492-500
The intertidal wormSipunculus nudus was exposed to various temperatures for an analysis of the integrated changes in energy and acid-base status. Animals were
incubated in sea water or maintained for up to 8 days at 4 and 0°C while dwelling in the sediment. Cannulation of the animals
prior to experimentation allowed the analysis of blood gas parameters (
,
and pH).
fell to 0 torr within 8 days at 0°C. A simultaneous reduction of ventilatory activity was derived from measurements of the
pattern of coelomic fluid pressure changes associated with ventilatory movements. The increase in
and an onset of anaerobic metabolism, indicated by the accumulation of end products like acetate and propionate both in the
coelomic fluid and the body wall musculature, led to the development of a progressive acidosis and a deviation from the alphastat
regulation of intracellular pH seen in unburied animals. The drop in intracellular pH together with the depletion of the adenylates
and the phosphagen, phospho-l-arginine, reflect a significant decrease in the Gibb's free-energy change of ATP hydrolysis. These changes are interpreted
to indicate lethal cold injuries, because recovery was not possible when the animals were returned to 12°C after more than
2 days of exposure to 0°C. A low critical temperature indicating the onset of cold-induced anaerobiosis is concluded to exist
below 4°C owing to the insufficient response of the ventilatory system to the developing hypoxia. 相似文献
35.
水稻伸长生长的数学模型 总被引:3,自引:1,他引:2
水稻地上部诸器官的伸长生长,可以分为3个阶段和两个过渡期.器官在前期的凹型曲线生长为加速生长(定为第1阶段),中期的直线生长为等速生长(第2阶段),后期的凸型曲线生长为减速生长(第3阶段);每两个阶段临界处均存在特殊的生长过程,前面的定为第1过渡期,做变加速生长,后面的定为第2过渡期,做变减速生长.组成器官的各个细胞的伸长生长,也可以分为前期凹型曲线阶段、中期的直线阶段以及这两个阶段临界处的过渡期.运用类比原理推断;细胞在凹型曲线阶段,其原生质的膨压大于壁压,而且这两个压差始终维持稳定,这就使细胞做等加速生长;细胞经过过渡期的变加速生长过渡到直线生长阶段,在这个阶段中,膨压大小与壁压相等,这就使细胞以过渡期最末的生长速度做等速生长;最后壁压大于膨压,而且这两个相差压会阻止细胞的“惯性”生长直至停止生长,其结果产生减速生长. 相似文献
36.
We show that the voltage-gated K+ and Ca2+ currents of rat osteoblastic cells are strongly modulated by arachidonic acid (AA), and that these modulations are very sensitive to the AA concentration. At 2 or 3 μm, AA reduces the amplitude and accelerates the inactivation of the K+ current activated by depolarization; at higher concentrations (≥5 μm), AA still blocks this K+ current, but also induces a very large noninactivating K+ current. At 2 or 3 μm, AA enhances the T-type Ca2+ current, close to its threshold of activation, whereas at 10 μm, it blocks that current. AA (1–10 μm) also blocks the dihydropyridine-sensitive L-type Ca2+ current. Thus, the effect of AA on Ca2+ entry through voltage-gated Ca2+ channels can change qualitatively with the AA concentration: at 2 or 3 μm, AA will favor Ca2+ entry through T channels, both by lowering the voltage-gated K+ conductance and by increasing the T current, whereas at 10 μm, AA will prevent Ca2+ entry through voltage-gated Ca2+ channels, both by inducing a K+ conductance and by blocking Ca2+ channels. 相似文献
37.
Mark A. Borchardt 《Journal of phycology》1994,30(3):418-430
The effects of flowing water on net photosynthesis, dark respiration, specific growth rate, and optimum N:P ratios by Spirogyra fluviatilis Hilse were assessed. The alga was cultivated under nitrogen or phosphorus limitation in laboratory streams at three flow velocities: 3, 12, and 30 cm·s?1. The Droop equation adequately described respiration and photosynthesis (PSnet) as a function of N or P cell quota (QN or Qp). The data show that for N- or P-limited Spirogyra fluviatilis, flowing water is physiologically costly. Generally, flowing water had little effect on respiration rates; however, the proportion of gross photosynthesis devoted to dark respiration did increase with flow velocity. For photosynthesis, the minimum N and P cell quotas increased with velocity, and the theoretical PSnet maxima for N and P both appeared greatest at 12 cm·s?1. The Droop models showed that for any given QN or Qp, PSnet, was reduced by the 30-cm·s?1 treatment. Consistent with this finding, independent estimates of specific growth rates for P-limited S. fluviatilis in the laboratory streams were inversely related to flow velocity when ambient PO4?3 was undetectable. However, growth was not diminished at the fastest velocity when PO4?3 was available for uptake. Thus, the increase in cellular phosphorus demand can be offset by flow-enhanced P uptake when conditions permit; otherwise, growth will be impaired. The optimum N:P ratios for S. fluviatilis at 3, 12, and 30 cm·s?1 were 50, 58, and 52 by atoms, respectively, when calculated for PSnet= 0. The optimum ratios were inversely related to PSnet and decreased to approximately 20 when PSnet was near maximum. The potential for flowing water to mediate nutrient partitioning among lotic algae by altering growth rates and optimum nutrient ratios is discussed. 相似文献
38.
Summary The electrical properties of the vacuolar membrane of the primitive green algaEremosphaera virdis were investigated using the patch-clamp technique. In whole vacuole measurements two types of transport systems with long activation time-constants were identified. The first, showing marked outward rectification, was activated by an increase in the cytosolic calcium concentration. Furthermore, it displayed sensitivity to micromolar concentrations of the anion channel blocker Zn2+ and to acidification of the cytosol. In contrast, the second time-activated current component was almost insensitive to changes in cytosolic pH and was blocked by the potassium channel inhibitor TEA. In addition to these slowly activating current components, the vacuolar membrane contained at least two further transport systems, responsible for an instantaneous current. These two current components were distinguished by their different sensitivity to protons, cytosolic calcium, and TEA. Comparing these electrical properties to those observed in vacuoles of higher plants or in cytoplasmic droplets from characean algae, respectively, it seems thatEremosphaera is intermediate, corresponding to the systematic position of this simple green alga.Abbreviations [Ca2+]cyt
cytosolic free calcium concentration
- EGTA
ethyleneglycol-bis(-aminoethylether)N,N,N,N-tetraacetic acid
- HEPES
N-[2-hydroxyethyl]piperazine-N-[2-ethanesulfonic acid]
- I
electric current
- IRC
inward rectifying current
- MES
2-[N-morpholino]ethanesulfonic acid
- ORC
outward rectifying current
- pHcyt
cytosolic pH
- pHvac
vacuolar pH
- Po
open probability
- Px
permeability coefficient of ion species X
- TEA
tetraethylammonium chloride
- Tris
tris[hydroxymethyl]aminomethane
- V
voltage 相似文献
39.
Summary Plasmalemmal ionic currents from enzymatically-isolated protoplasts of suspension-cultured carrot cells were investigated by patch-clamp techniques. Among other currents, a novel hyperpolarization-activated, inwardly-rectifying, whole-cell current was observed. The activation of this current was fast in onset, and for large hyperpolarizations a characteristic, rapid voltage-dependent inactivation was seen. Ion substitution experiments indicate that this inward current was due mainly to efflux of chloride ions. No dependence on either internal or external calcium was found, and internal MgATP was not necessary. Surprisingly, zinc did not block this current. In hyperpolarized outside-out patches, inward single-channel chloride currents having an elementary conductance of ca. 100 pS were observed. The open probability increased with hyperpolarization. Similar single-channel currents were activated by slight negative pressure applied to the pipette. These chloride currents could contribute both to the control of membrane potential and in the regulation of osmotic balance in carrot cells.Abbreviations BAPTA
1,2-bis (2-aminophenoxy)ethane-N,N,N,N-tetraacetic acid
- 2,4-D
2,4-dichlorophenoxyacetic acid
- Ex
Nernst equilibrium potential for ion x
- NMDG
N-methyl-D-glucamine
- PMSF
phenylmethylsulfonyl fluoride 相似文献
40.
D. E. Doan Y. E. Cohen J. C. Saunders 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1994,174(1):103-110
Laser interferometry was used to measure umbo velocity in the developing BALB/c mouse middle ear at 133 pure-tone frequencies between 2.0 kHz and 40.0 kHz, all at a constant 100 dB sound pressure level. Umbo velocities increased with age across the entire frequency range, and reached adult-like levels by about 19 days between 2.0 and 22.0 kHz. Velocities at 28.0 and 34.0 kHz took 27 and 52 days respectively to reach adult-like levels.A simple middle-ear model utilizing compliance, resistance, and inertia elements matched the general trends of our velocity results and provided an indication of the anatomical basis for the growth in umbo velocity. The model suggested that velocity development at the lowest frequencies may be attributed to increases in tympanic membrane compliance. The model also indicated that both the frictional resistance of the middle ear and the inertia of the tympanic membrane and ossicles decreased during the growth period.At frequencies below 20.0 kHz, age-related increases in umbo velocity coincided with improvements in Nj1 thresholds recorded from the round window and evoked potential thresholds obtained from the cochlear nucleus. These results indicated that the functional development of the middle-ear plays a major role in the development of hearing in the mouse.Portions of this work were presented at the Fifteenth Meeting of the Association for Research in Otolaryngology 相似文献