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1.
A vasoactive intestinal peptide-sensitive adenylate cyclase in intestinal epithelial cell membranes was characterized. Stimulation of adenylate cyclase activity was a function of vasoactive intestinal peptide concentration over a range of 1 · 10−10−1 · 10−7 M and was increased six-times by a maximally stimulating concentration of vasoactive intestinal peptide. Half-maximal stimulation was observed with 4.1 ± 0.7 nM vasoactive intestinal peptide. Fluoride ion stimulated adenylate cyclase activity to a higher extent than did vasoactive intestinal peptide. Under standard assay conditions, basal, vasoactive inteetinal peptide- and fluoride-stimulated adenylate cyclase activities were proportional to time of incubation up to 15 min and to membrane concentration up to 60 μg protein per assay. The vasoactive intestinal peptide-sensitive enzyme required 5–10 mM Mg2+ and was inhibited by 1 · 10−5 M Ca2+. At sufficiently high concentrations, both ATP (3 mM) and Mg2+ (40 mM) inhibited the enzyme.Secretin also stimulated the adenylate cyclase activity from intestinal epithelial cell membranes but its effectiveness was 1/1000 that of vasoactive intestinal peptide. Prostaglandins E1 and E2 at 1 · 10−5 M induced a two-fold increase of cyclic AMP production. Vasoactive intestinal peptide was the most potent stimulator of adenylate cyclase activity, suggesting an important physiological role of this peptide in the cyclic AMP-dependent regulation of the intestinal epithelial cell function.  相似文献   

2.
Mg2+, Ca2+ and Mn2+ were found to act as activators of the ATP-dependent surface reaction, leading to head-to-head association in bull spermatozoa. Ca2+ was more efficient than Mg2+, while Zn2+, like Na+ + K+ in combination with Mg2+, seemed to have no such effect. High ionic strength induced head-to-head association, as did higher concentrations of Mg2+ and Ca2+ than those necessary for the activation of ATP, Ca2+ acting in a lower conc. than Mg2+. To this effect was added that of the ATP-dependent reaction when ATP was also present. As activators, Mg2+ and Ca2+ did not potentiate each other; their effects were cumulative when the ions acted together.When the ATP concentration within the range 1 × 10−5 to 8 × 10−5 M was increased stepwise in the presence of 2 × 10−5 M Mg2+ or Ca2+, the association resulting from each single concentration step progressively increased. At low cation concentrations, the increase was about the same for the two cations: at higher concentrations it was much steeper in the presence of Ca2+ than in that of Mg2+. In the latter case, it was not statistically significant above 4 × 10−5 M ATP.Increasing the cation concentration in the range 1 × 10−5 to 4 × 10−5 M in the presence of 2 × 10−5 M ATP produced an immediate high increase in association, which was followed by a lower increase. The optimum concentration ratio for Mg2+:ATP was at least 1:1 and for Ca2+: ATP at least 1.5:1.Oubain, containing enone structure, abolishes association.  相似文献   

3.
Cells were subjected to a range of 45Ca2+ influx loads with A23187. We measured cell 45Ca2+ with time and A23187 dose, and the apparent 45Ca2+ influxes (≡“J(in,app)”) at Ca2+ steady state. We also measured endogeneous exchangeable and total cell Ca2+, which were 50 and 17–220 μM respectively. The effects of A23187 and Ca2+ on cell ATP, swelling, net Cl permeability, and cell morphology were measured. These were modest and do not affect our conclusions.J(in,app) 3 × 10−4 [A23187]2.9·[Ca2+(o)]μmoles/l·min with 92–552 μM [Ca2+(o)] (≡ external Ca2+ concentration) and 0–7 μM A23187. J(in,app) was increased an order of magnitude by vanadate and is probably much less than the true influx. The least unlikely explanation found for the high [A23187] exponent, 2.9, was that most of the Ca2+ crossing the membrane is expelled by the pump before it can move deeper into the cell.Calcium pumping increased rapidly in response to increased influx, but the steady state cell 45Ca2+ was approximately proportional to J(in,app) rather than approximately constant between 10 and 120 μmoles/l·min with 184 μM [Ca2+(o)]. This is not the result expected from a simple feedback mechanism.At high A23187 doses the pump appears fully activated resulting in a linear relation between cell/medium 45Ca2+ and [A23187]−2. From the plot we calculated α≡free/total exchangeable Ca2+ = 0.38 ± 0.08 (n = 3) and a maximum pump rate, “Pmax” = 78 μmole/l·min. Pmax is underestimated insofar as J(in,app) is less than the true influx.  相似文献   

4.
A fluorescent sensor, 5, based upon the sugar-aza-crown ether structure with two anthracenetriazolymethyl groups was prepared and its fluoroionophoric properties toward transition metal ions were investigated. In methanol, the sensor exhibits highly selective recognition of Cu2+ and Hg2+ ions among a series of tested metal ions. The association constant for Cu2+ and Hg2+ in methanol was calculated to be 4.0 × 105 M−1 and 1.1 × 105 M−1, respectively. The detection limits for the sensing of Cu2+ and Hg2+ ions were 1.39 × 10−6 M and 1.39 × 10−5 M, respectively.  相似文献   

5.
Thyroid hormone (T3) has been demonstrated to inhibit the action of aldosterone on sodium transport in toad urinary bladder and rat kidney. We have exammined the effect of T3 on aldosterone action and specific nuclear binding in cultured epithelial cells derived from toad urinary bladder. In cell line TB6-C, addition of 5·10−8 M T3 to culture media for up to 3 days results in no change in short-circuit current or transepithelial resistance. This concentration of T3 completely inhibits the maximal increase in short-circuit current in response to 1·10−7 M aldosterone. The inhibition can be demonstrated with 18 h preincubation or with simultaneous addition of T3 and aldosterone. The half-maximal concentration for the inhibition of the aldosterone effect is approx. 5·10−9 M T3. T3 has no effect on cyclic AMP-stimulated short-circuit current in these cells. The effect of T3 on nuclear binding of [3H]aldosterone was examined using a filtration assay with data analysis by at least-squares curve-fitting program. Best fit was obtained with a model for two binding sites. The dissociation constants for the binding were Kd1 = (0.82 ± 0.36)·10−10 M and Kd2 = (3.2±0.60)·10−8 M.The half-maximal concentration for aldosterone-stimulated sodium transport in these cells is approx. 1·10−8 M. Analysis of nuclear aldosterone binding in cells preincubated for 18 h with 5·10−8 M T3 showed a Kd1 = (0.15 ± 0.10)·10−10 M and Kd2 = (3.5 ± 0.10)·10−8 M. We conclude that T3 i action of aldosterone on sodium transport at a site after receptor binding in the nucleus.  相似文献   

6.
Changes in guanosine cyclic 3′,5′-monophosphate associated with adenosine cyclic 3′,5′-monophosphate and folic acid addition in the presence of ATP have been examined in Dictyostelium discoideum. Preincubation with 1 mM ATP had no effect on the basal cyclic GMP level but increased the cycli GMP accumulation in response to cylci AMP (5·10−8 M) or folic acid (5·10−6 M) 40–50%. ATP could not be replaced by ADP of 5′-adenylyliminodiphosphate. Because ATP has no effect on cyclic AMP receptor binding these results indicate that structural membrane alterations (e.g. membrane phosphorylation) may control the transduction of a chemotactic signal.  相似文献   

7.
Membrane Ca2+-ATPase activity was stimulated in vitro separately by T4 (10−10 M) and by epinephrine (10−6 M). In the presence of a fixed concentration of T4, additions of 10−8 and 10−6 M epinephrine reduced the T4 effect on the enzyme. β-Adrenergic blockade with propranolol (10−6 M) prevented stimulation by epinephrine of Ca2+-ATPase activity, but did not prevent the suppressive action of epinephrine on T4-stimulable Ca2+-ATPase. In contrast α1-adrenergic blockade with unlabelled prazosin restored the effect of T4 on Ca2+-ATPase activity in the presence of epinephrine. Like propranolol, prazosin prevented enhancement of enzyme activity by epinephrine in the absence of thyroid hormone. Neither prazosin nor propranolol had any effect on the stimulations by T4 of red cell Ca2+-ATPase in the absence of epinephrine. Analysis of radiolabelled prazosin binding to human red cell membranes revealed the presence of a single class of high-affinity binding sites (Kd, 1.2 × 10−8 M; Bmax, 847 fmol/mg membrane protein). Thus, the human erythrocyte membrane contains α1-radrenergic receptor sites that are capable of regulating Ca2+-ATPase activity.  相似文献   

8.
Dispersed acini from dog pancreas were used to examine the ability of dopamine to increase cyclic AMP cellular content and the binding of [3H]dopamine. Cyclic AMP accumulation caused by dopamine was detected at 1·10−8 M and was half-maximal at 7.9±3.4·10−7M. The increase at 1·10−5 M, (7.5-fold) was equal to the half-maximal increase caused by secretin at 1·10−9 M. Haloperidol, a dopaminergic receptor antagonist inhibited cyclic AMP accumulation caused by dopamine. The IC50 value for haloperidol, calculated from the inhibition of cyclic AMP increase caused by 1·10−5 M dopamine was 2.3±0.9·10−6M. Haloperidol did not alter basal or secretin-stimulated cyclic AMP content. [3H]Dopamine binding was studied on the same batch of cells as cyclic AMP accumulation. At 37°C, it was rapid, reversible, saturable and stereospecific. The Kd value for high affinity binding sites was 0.43±0.1·10−7M and 4.7±1.6·10−7M for low affinity binding sites. The concentration of drugs necessary to inhibit specific binding of dopamine by 50% was 1.2±0.4·10/t-7M noradrenaline, 2·10/t-7 M epinine, 4.1±1.8·10/t-6M fluphenazine, 8.0±1.6·10/t-6M haloperidol, 4.2±1.2·10−6Mcis-flupenthixol, 2.7±0.4·10−5Mtrans-flupenthixol, >1·10−5M apomorphine, sulpiride, naloxone and isoproterenol.  相似文献   

9.
The bacteriophage PM2 requires extracellular Ca2+ at concentrations greater than 3 · 10−4 M for the production of viable virus, whereas the host cell Pseudomonas BAL-31 grows normally in medium containing 3 · 10−5 M Ca2+ (low calcium). Virus attachment occurs normally in low calcium, the infected cultures partially lyse, but no infectious virus particles are released. Sucrose gradient analysis shows that lysates made in low calcium contain no PM2-like particles. The addition of calcium very late in the infectious cycle completely restores virus production to cultures infected in low calcium, whereas removal of calcium after infection prevents virus production. Our experiments indicate that Ca2+ is essential for some process late in the lytic cycle, such as the final assembly of stable, infectious PM2 particles.  相似文献   

10.
The binding and inhibitory properties of 11 benzimidazoles for bovine brain tubulin were investigated. The effects of the benzimidazoles on the initial rates of microtubule polymerization were determined by a turbidimetric assay. The median inhibitory concentrations (I50) for nocodazole, oxibendazole, parbendazole, mebendazole and fenbendazole ranged from 1.97 · 10−6 to 6.32 · 10−6 M. Benomyl, cambendazole and carbendazim had I50 values from 5.83 · 10−5 to 9.01 · 10−5 M. Thiabendazole had an I50 value of 5.49 · 10−4 M. Inhibitor constants (Ki) were determined by the colchicine binding assay. Oxibendazole, fenbendazole, and cambendazole had Ki values of 3.20 · 10−5, 1.73 · 10−5 and 1.10 · 10−4 M, respectively. Oxibendazole and fenbendazole were competitive inhibitors of colchicine. In contrast, cambendazole was a noncompetitive inhibitor of colchicine. The ability of these benzimidazoles to inhibit microtubule polymerization and the mode of action for the anthelmintic benzimidazoles is discussed.  相似文献   

11.
The synthetic progestin 16α-ethyl-21-hydroxy-19-norpregn-4-ene-3,20-dione (Org 2058) was used to characterize the progesterone receptor in the uterine cytosol of the rabbit. [3H] Org 2058 binds to a homogeneous population of protin binding sites with an apparent association equilibrium constant of 7.7· 108 M−1 at 0°C. The concentration of protein-bound steroid at saturation is 2.3 pmol per mg of cytosol protein. [3H] Progesterone binds to the same set of binding sites but exhibits a 4–5 fold lower apparent association constant. The difference in affinity is mainly due to a 13-fold slower rate of dissociation of the synthetic progestin compared with progesterone. Org 2058 competes very efficiently for the binding of [3H] progesterone to the uterine cytosol, and progesterone also competes, although less efficiently, for the binding of [3H]-Org 2058. There is a good correlation between the progestational activity of various steroids and their ability to compete with [3H] Org 2058 binding to the cytosol. At 0°C, there is no metabolic transformation of either Org 2058 or progesterone in the uterine cytosol.When filled with the steroid, the progesterone receptor is stable, but in the absence of the steroid the receptor binding sites are thermolabile and show a rapid decay at 20°C . Org 2058 is more effective than progesterone in protecting the receptor against thermal inactivation. The rate constant of association and dissociation of [3H] Org 2058 and the cytosol receptor are strongly dependent on temperature and the activation energy of the dissociation reaction is 17.8 kcal/mol. The equilibrium association constant is less dependent on temperature and exhibits ΔH° of −4.7 kcal/mol. The binding reaction shows a positive entropy change of 23 cal · K−1 · mol−1.At low ionic strength the complex of Org 2058 and the progesterone receptor tends ot aggregate. It sediments as a broad peak on sucrose gradients (4–6 S), and is excluded from columns of Sephadex G-100 and G-200. At concentrations of NaCl above 0.15 M, the receptor sediments in sucrose gradients as an homogeneous peak at 3.6 S, but upon gel filtration it aggregates and a complex elution pattern is observed, that prevents a precise estimation of the molecular weight.  相似文献   

12.
Active transport of Cl accounts for 90% of the short-circuit current (s.c.c.) in the isolated frog cornea. 1·10−5 M furosemide produced a 50% reversible inhibition of this s.c.c. 1·10−4 M ethacrynic acid reduced the corneal s.c.c. to 32% of the control. In the isolated frog skin epithelium furosemide had no effect on the s.c. at a concentration of 1·10−4 M and a small stimulation at a concentration of 1·10−3 M. The furosemide inhibitory effects seems to be specific for Cl, as it also inhibits Cl transport in the ascending limb of the loop of Henle (Burg, M.B. (1972) Proc. 5th Int. Congr. Nephrol., p. 50, Abstr.).  相似文献   

13.
We studied PGE2 specific binding sites in human myometrial microsomes prepared from uterine specimens obtained by hysterectomy (women between 38 and 55 years of age). Competition experiments showed that the potency order for various prostaglandins (PGs) was : PGE2 ≥ PGE1 PGF > Iloprost ≥ Carbacyclin ZK 110841 (PGD2 analogue). These relative affinities indicated that the receptor was of the EP type.In kinetic experiments GTP, GppNHp and GTPγS increased the rate of PGE2 binding (steady state was reached more rapidly in the presence of nucleotides) but maximal specific binding was not significantly different. Complete dissociation could not be obtained, even in the presence of GTP. Only 50% of maximal binding was readily dissociable. The dissociation rate was 4.56.10−4 sec−1 (half time of about 660 sec) and in the presence of GTP analogues it was slightly increased (k−1 = 7.16 10−4 sec−1 half time 420 sec.). Scatchard analysis of saturation curves showed an increase in ligand receptor affinity in the presence of GTP or nucleotide analogues: the Kd shifted from 9.66 ± 2.8.10−9 M to 4.96 ± 1.25.10−9M, but the number of binding sites did not change significantly (310 ± 37 to 350 ± 17 fmol/mgP). The effect of GTP was observed at a concentration of 5.10−4M. GppNHp and GTPγS were effective at 1.10−5M. Pretreatment of myometrial membranes with pertussis or cholera toxins had no effect on PGE2 binding to membrane sites. Our conclusion is that GTP induced conversion of a population of low affinity sites into a population of higher affinity sites. This effect of guanine nucleotides was described in adipocytes and kidney medulla.Competition studies with PGE2 analogues (sulprostone, 17-phenyl-ω-trinor PGE2, M&B 28,767, misoprostol, butaprost) showed that this receptor mediates a contractile response and is probably an EP3 subtype.  相似文献   

14.
We have previously reported that angiotensin II (ANG II) induces oscillations in the cytoplasmic calcium concentration ([Ca2+]i) of pulmonary vascular myocytes. The present work was undertaken to investigate the effect of ANG II in comparison with ATP and caffeine on membrane currents and to explore the relation between these membrane currents and [Ca2+]i. In cells clamped at −60 mV, ANG II (10 μM) or ATP (100 μM) induced an oscillatory inward current. Caffeine (5 μM) induced only one transient inward current. In control conditions, the reversal potential (Erev) of these currents was close to the equilibrium potential for Cl ions (ECl = −2.1 mV) and was shifted towards more positive values in low-Cl solutions. Niflumic acid (10–50 μM) and DIDS (0.25-1 mM) inhibited this inward current. Combined recordings of membrane current and [Ca2+]i by Indo-1 microspectrofluorimetry revealed that ANG II- and ATP-induced currents occurred simultaneously with oscillations in [Ca2+]i, whereas the caffeine-induced current was accompanied by only one transient increase in [Ca2+]i Niflumic acid (25 μM) had no effect on agonist-induced [Ca2+]i responses, whereas thapsigargin (1 μM) abolished both membrane current and the [Ca2+]i response. Heparin (5 mg/ml in the pipette solution) inhibited both [Ca2+]i responses and membrane currents induced by ANG II and ATP, but not by caffeine. In pulmonary arterial strips, ANG II-induced contraction was inhibited by niflumic acid (25 μM) or nifedipine (1 μM) to the same extent and the two substances did not have an additive effect. This study demonstrates that, in pulmonary vascular smooth muscle, ANG II, as well as ATP, activate an oscillatory calcium dependent chloride current which is triggered by cyclic increases in [Ca2+]i and that both oscillatory phenomena are primarily IP3 mediated. It is suggested that ANG II-induced oscillatory chloride current could depolarise the cell membrane leading to activation of voltage-operated Ca2+ channels. The resulting Ca2+ influx contributes to the component of ANG II-induced contraction that is equally sensitive to chloride or calcium channel blockade.  相似文献   

15.
The antagonistic effect of calcium (Ca2+), zinc (Zn2+) and selenium (Se4+) at different concentrations (10−2–10−6 M) against cadmium (Cd2+) induced genotoxic effects in root cells of Hordeum vulgare were studied. The results showed that 10−3–10−5 M could induce chromosomal aberrations and micronuclei formation. But in the treatment with 10−2–10−6 M of Ca2+, Zn2+ and Se4+ together with Cd2+ (10−3–10−5 M), respectively, the frequencies of chromosomal aberrations and micronuclei effectively decreased after 48 h of treatment. The treatment with 10−4–10−6 M of Ca2+ together with 10−4–10−5 M Cd2+, 10−6 M of Zn2+ together with 10−5 M Cd2+ and 10−6 M of Se4+ together with 10−5 M Cd2+ suggested rather obvious antagonistic effects. The order of the antagonisms of Ca2+, Se4+ and Zn2+ against Cd2+ toxicity was Ca2+>Se4+>Zn2+. The degree of antagonisms of Ca2+, Se4+ and Zn2+ against Cd2+ related to their concentration ratio.  相似文献   

16.
Glycerol diffusional permeabilities through the cytoplasmic cell membrane of Dunaliella salina, the cell envelope of pig erythrocyte and egg phosphattidylcholine vesicles were measured by NMR spectroscopy employing the spin-echo method and nuclear T1 relaxation. The following permeability coefficients (P) and corresponding enthalpies of activation (ΔH) were determined for glycerol at 25°C: for phosphatidylcholine vesicles 5·10−6 cm/s and 11±2 kcal/mol; for pig erythrocytes 7·10−8 cm/s and 18±3 kcal/mol, respectively; for the cytoplasmic membrane of D. salina the permeability at 17°C was found to be exceptionally low and only a lower limit (P<5·10−11cm/s) could be calculated. At temperatures above 50°C a change in membrane permeability occurred leading to rapid leakage of glycerol accompanied by cell death. The data reinforce the notion that the cytoplasmic membrane of Dunaliella represents a genuine anomaly in its exceptional low permeability to glycerol.  相似文献   

17.
In this study, the hydraulic conductivity (Lp), Me2SO permeability ( Me2SO), and the reflection coefficients (ς) and their activation energies were determined for Metaphase II (MII) mouse oocytes by exposing them to 1.5 M Me2SO at temperatures of 30, 20, 10, 3, 0, and −3°C. These data were then used to calculate the intracellular concentration of Me2SO at given temperatures. Individual oocytes were immobilized using a holding pipette in 5 μl of an isosmotic PBS solution and perfused with precooled or prewarmed 1.5 M Me2SO solutions. Oocyte images were video recorded. The cell volume changes were calculated from the measurement of the diameter of the oocytes, assuming a spherical shape. The initial volume of the oocytes in the isoosmotic solution was considered 100%, and relative changes in the volume of the oocytes after exposure to the Me2SO were plotted against time. Mean (means ± SEM) Lpvalues in the presence of Me2SO ( Me2SOp) at 30, 20, 10, 3, 0, and −3°C were determined to be 1.07 ± 0.03, 0.40 ± 0.02, 0.18 ± 0.01, 7.60 × 10−2± 0.60 × 10−2, 5.29 × 10−2± 0.40 × 10−2, and 3.69 × 10−2± 0.30 × 10−2μm/min/atm, respectively. The Me2SOvalues were 3.69 × 10−3± 0.3 × 10−3, 1.07 × 10−3± 0.1 × 10−3, 2.75 × 10−4± 0.15 × 10−4, 7.83 × 10−5± 0.50 × 10−5, 5.24 × 10−5± 0.50 × 10−5, and 3.69 × 10−5± 0.40 × 10−5cm/min, respectively. The ς values were 0.70 ± 0.03, 0.77 ± 0.04, 0.81 ± 0.06, 0.91 ± 0.05, 0.97 ± 0.03, and 1 ± 0.04, respectively. The estimated activation energies (Ea) for Me2SOp, Me2SO, and ς were 16.39, 23.24, and −1.75 Kcal/mol, respectively. These data may provide the fundamental basis for the development of more optimal cryopreservation protocols for MII mouse oocytes.  相似文献   

18.
Ionophore A23187-mediated Ca2+-induced oscillations in the conductance of the Ca2+-sensitive K+ channels of human red cells were monitored with ion specific electrodes. The membrane potential was continuously reflected in CCCP-mediated pH changes in the buffer-free medium, changes in extracellular K+ activity were followed with a K+-selective electrode, and changes in the intracellular concentration of ionized calcium were calculated on the basis of cellular 45Ca content. An increased cellular 45Ca content at the successive minima of the oscillations where the K+ channels are closed indicates that the activation of the channels might be a (dCa2+/dt)-sensitive process and that accommodation to enhanced levels of intracellular free calcium may occur. An incipient inactivation of the K+ channels at intracellular ionized calcium levels of about 10 μM and a concurrent membrane potential of about −65 mV was observed. At a membrane potential of about −70 mV and an intracellular concentration of about 2·10−4M no inactivation of K+ channels took place. Inactivation of the K+ channels is suggested to be a compound function of the intracellular level of free calcium and the membrane potential. The observed sharp peak values in cellular 45Ca content support the notion that a necessary component of the oscillatory system is a Ca2+ pump operating with a significant delay in the activation/inactivation process in response to changes in cellular concentration of ionized calcium.  相似文献   

19.
Calcium efflux has been studied in barnacle muscle fibres under internal dialysis conditions. Prolonged dialysis of these fibres, with a medium free of ATP and containing 2 mM cyanide and 1 mM iodoacetate, causes the ATP in the perfusion effluent to fall to less than 20 μM. The mean calcium efflux from fibres dialyzed with EGTA buffered solution containing 0.3 μM ionized Ca and no ATP is 0.6 pmol · cm−2 · s−1. A two-fold stimulation of the calcium efflux is observed when ATP is added to fibres previously dialyzed with an ATP-free medium. Withdrawal of Na+ and Ca2+ from the external medium causes a marked drop in the Ca2+ efflux in the presence of internal ATP.  相似文献   

20.
K. Kuroda  S. Sonobe 《Protoplasma》1981,109(1-2):127-142
Summary Motile models ofAmoeba proteus prepared by extraction at –20 °C with a 50% buffered glycerol solution showed remarkable contraction on addition of Mg-ATP with retainment of Ca++ sensitivity. The initial contraction around the nucleus occurred on addition of Mg-ATP independently of the Ca++ concentration, and was followed by contractions of three different patterns. In 10–8M Ca++, the granuloplasm contracted as a whole and separated from the membrane leaving no detectable particles in the anterior region. In 10–6M Ca++, the granuloplasm contracted leaving some granules which showed active and vigorous two-directional streaming similar to that in the living cell. Sometimes a part of the plasma membrane twitched. The streaming lasted up to 20 minutes. In 10–4M Ca++, after the initial contraction around the nucleus, no significant movement was observed. All these movements in the models were inhibited by cytochalasin B or N-ethylmaleimide. The relationship between the Mg-ATP and the Ca++ concentrations was examined.  相似文献   

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