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1.
R Simantov 《Life sciences》1978,23(25):2503-2508
Mouse pituitary tumor cells grown in tissue culture release endorphins spontaneously to the culture medium. Depolarization of these cells by incubation with high K+ concentration (56 mM) increased 2–3 folds the release of endorphins. The K+ evoked release was Ca++ dependent by that: a, removal of Ca++ ions inhibited 90% of K+ stimulated release. b, ethyleneglycol-bis (β-aminoethyl ether) N,N′-tetraacetic acid (EGTA) inhibited release of endorphins in the presence of high K+ and Ca++. It is suggested that dual regulatory system inhibit and/or stimulate in-vivo release of endorphins from the pituitary glands.  相似文献   

2.
White erythrocyte membranes, or ghosts, were monoconcave discocytes when incubated in 50mM N-tris (hydroxymethyl) methyl-2-aminoethane sulfonic acid titrated to pH 7.4 with triethanolamine. If 3mM MgCl2 was included in the incubation medium, the ghosts were predominantly echinocytes. The echinocytic form could also be induced by Co++, Ni++, Li+, Na+, K+, NH4+ and tetramethylammonium ion, all as chloride salts. The concentration of cation necessary for 50% of the ghosts to be echinocytes was correlated with the hydrated charge density of the cation with the most highly charged cations being the most effective. The cations Ca++, Sr++, Ba++ and La+++, (also as chloride salts) did not induce the normal echinocytic form, but at high levels induced a few misshapen forms with some resemblance to echinocytes. Instead Ca++, Sr++, Ba++ and La+++ suppressed the formation of echinocytes in the presence of Mg++ and other ions. This suggests the presence of a specific Ca++ binding site important to shape control in the erythrocyte membrane.  相似文献   

3.
A novel method for the preparation of intact chromatin from the slime mold Physarumpolycephalum> which retains the invivo property of RNA synthesis is described. Preparations from G2-cells were highly active, while those from metaphase-cells were inactive. The plasmodial cells were disrupted by gentle homogenization on a polyethylene sieve in a neutral isotonic sucrose medium containing Mg++, deoxycholate and EGTA, a Ca++-chelating agent. The nuclei were lysed in a hypotonic buffer without use of EDTA and chromatin was precipitated by centrifugation after addition of Mg++.  相似文献   

4.
We employed the calcium (Ca++)-sensitive, intracellular dye QUIN-2 to examine the role of cytosolic Ca++ in the stimulation of PTH release by high extracellular potassium (K+) concentrations. Addition of 55 mM KCl to cells incubated with 115 mM NaCl and 5 mM KCl lowered cytosolic Ca++ at either low (0.5 mM) extracellular Ca++ (from 194±14 to 159±9 nM, p<.01, N=6) or high (1.5 mM) extracellular calcium (from 465±38 to 293±20 nM, p<.01, N=10). This reduction in cytosolic Ca++ was due to high K+perse and not to changes in tonicity since addition of 55 mM NaCl was without effect while a similar decrease in cytosolic Ca++ occurred when cells were resuspended in 60 mM NaCl and 60 mM KCl. PTH release was significantly (p<.01) greater at 0.5 and 1.5 mM Ca++ in QUIN-2-loaded cells incubated with 60 mM NaCl and 60 mM KCl than in those exposed to 115 mM NaCl and 5 mM KCl. In contrast to most secretory cells, therefore, stimulation of PTH release by high K+ is associated with a decrease rather than an increase in cytosolic Ca++.  相似文献   

5.
Micropuncture and microanalytical methods were employed to investigate the rôle of the spermathecal epithelium of the honey queen-bee in providing the appropriate conditions for the prolonged storage of spermatozoa. It was found that the epithelium maintains large concentration gradients of inorganic ions, generates an electrical potential difference of 21 mV, lumen positive, and produces a pH difference of up to 2.4 pH units between spermathecal fluid (SF) and haemolymph (H). The SFH concentration ratios for K+, Na+, Ca++, Cl?1, HPO4??, H2PO4? and amino acids were 7.7; 0.5; 0.8; 0.4; 1.03; 0.004; 0.3, respectively. While the pH value of haemolymph was constant at 6.17, the pH of SF increased with age from 7.3 to 8.6 over the first 3 days. The calculated electrochemical potential differences suggest that the epithelium of the spermathecal wall secretes K+ (and possibly HCO3? or OH?) actively into the lumen, but handles Na+ passively. This pattern conforms with the organization of ion transport in other insects.  相似文献   

6.
Lanthanum (0.25 mM) does not penetrate into fresh or Mg2+-depleted cells, whereas it does into ATP-depleted or ATP + 2,3-diphosphoglycerate-depleted cells, into cells containing more than 3 mM calcium, or cells stored for more than 4 weeks in acid/citrate/dextrose solution. In fresh cells loaded with calcium, extracellular lanthanum blocks the active Ca2+-efflux completely and inhibits (Ca2+ + Mg2+)-ATPase (ATP phosphohydrolase, EC 3.6.1.3) activity to about 50%. In Mg2+-depleted cells Ca2+-Ca2+ exchange is inhibited by lanthanum. Ca2+-leak is unaffected by lanthanum up to 0.25 mM concentration; higher lanthanum concentrations reduce leak rate. In NaCl medium Ca2+-leak ± S.D. amounts to 0.28 ± 0.08 μmol/l of cells per min, whereas in KCl medium to 0.15 ± 0.04 μmol/l of cells per min at 2.5 mM [Ca2+]e and 0.25 mM [La3+]e pH 7.1.Lanthanum inhibits Ca2+-dependent rapid K+ transport in ATP-depleted and propranolol-treated red cells, i.e. whenever intracellular calcium is below a critical level. The inhibition of the rapid K+ transport can be attributed to protein-lanthanum interactions on the cell surface, since lanthanum is effectively detached from the membrane lipids by propranolol.Lanthanum at 0.2–0.25 mM concentration has no direct effect on the morphology of red cells. The shape regeneration of Ca2+-loaded cells, however, is blocked by lanthanum owing to Ca2+-pump inhibition. Using lanthanum the transition in cell shape can be quantitatively correlated to intracellular Ca2+ concentrations.  相似文献   

7.
The NADP+ specific glutamate dehydrogenase from wild-type Neurospora crassa forms a stable binary complex with NADPH. This can combine with L-glutamate, α-ketoglutarate or the substrate analogue D-glutamate to form ternary complexes which can be distinguished by their different fluorescence properties. The affinity of the enzyme for NADPH diminishes with increases in pH or ionic strength of the solution. Experimental data obtained using modified glutamate dehydrogenases from mutant strains of N. crassa suggest that the reduced-coenzyme binding sites observed fluorimetrically are the same as those observed by enzyme kinetics.  相似文献   

8.
Ca2+ transport was studied in membrane vesicles of alkalophilic Bacillus. When Na+-loaded membrane vesicles were suspended in KHCO3/KOH buffer (pH 10) containing Ca2+, rapid uptake of Ca2+ was observed. The apparent Km value for Ca2+ measured at pH 10 was about 7 μM, and the Km value shifted to 24 μM when measured at pH 7.4. The efflux of Ca2+ was studied with Ca2+-loaded vesicles. Ca2+ was released when Ca2+-loaded vesicles were suspended in medium containing 0.4 M Na+.Ca2+ was also transported in membrane vesicles driven by an artificial pH gradient and by a membrane potential generated by K+-valinomycin in the presence of Na+.These results indicate the presence of Ca2+/Na+ and H+/Na+ antiporters in the alkalophilic Bacillus A-007.  相似文献   

9.
The membrane potential generated at pH 8.5 by K+-depleted and Na+-loaded Vibrioalginolyticus is not collapsed by proton conductors which, instead, induce the accumulation of protons in equilibrium with the membrane potential. The generation of such a membrane potential and the accumulation of protons are specific to Na+-loaded cells at alkaline pH and are dependent on respiration. Extrusion of Na+ at pH 8.5 occurs in the presence of proton conductors unless respiration is inhibited while it is abolished by proton conductors at acidic pH. The uptake of α-aminoisobutyric acid, which is driven by the Na+-electrochemical gradient, is observed even in the presence of proton conductors at pH 8.5 but not at acidic pH. We conclude that a respiration-dependent primary electrogenic Na+ extrusion system is functioning at alkaline pH to generate the proton conductor-insensitive membrane potential and Na+ chemical gradient.  相似文献   

10.
Oxidative phosphorylation, active transport of proline, aerobic- and ATP-driven proton translocation and transhydrogenation of NADP+ by NADH, occurred in lipoic acid-deficient cells or vesicles of a lipoic acid auxotroph of E. coli, W1485 lip 2. Addition of lipoic acid had little effect on these processes. Tributyltin chloride, which has been proposed to inhibit oxidative phosphorylation by reaction with lipoic acid (Cain et al., Biochem. J. (1977) 166, 593), was an effective inhibitor of aerobic and ATP-dependent proton translocation and transhydrogenation in lipoic acid-deficient vesicles from this organism. Our results do not support the proposal of Partis et al. (FEBS Lett. (1977) 75, 47) that lipoic acid is involved in the energy transducing processes associated with the membrane of E. coli.  相似文献   

11.
The tumor promoter phorbol 12-myristate 13-acetate rapidly induces alterations in both Ca++ content and transport in cultured differentiated chick myoblasts. At 4 ng/ml (6nM), the promoter caused a 25 ± 12% decrease in total intracellular Ca++ within 5 h after its addition. Measurement of 45Ca++ transport at this time revealed a 15 ± 6% decrease in the rate constants for both efflux and influx. Values of t12 for the cytosolic Ca++ pool in control and treated cells were 9.1 and 10.7 min, respectively, for efflux and 8.6 and 10.4 min, respectively, for influx. Ca++ influx was decreased maximally within 90 sec after promoter addition. No effect was observed on 86Rb+ uptake or intracellular concentration at equilibrium. The Ca++ response is among the most rapid yet reported and may play a primary role in altering cellular metabolism.  相似文献   

12.
Synthesis of simian virus 40 DNA in isolated nuclei   总被引:1,自引:0,他引:1  
The presence or absence of calcium ions during the isolation of nuclei from SV40-infected African green monkey kidney cells significantly affects the size of SV40 DNA synthesized in vitro. When Ca++ is present during the nuclear isolation procedure, the 3–7S fragments of SV40 DNA synthesized in vitro mature into long chains; in the absence of Ca++ they do not.  相似文献   

13.
Purified enterotoxin from the bacterium Clostridium perfringens rapidly decreased the hormonally induced uptake of α-aminoisobutyric acid in primary cultures of adult rat hepatocytes. At 5 min after toxin addition the decrease in α-aminoisobutyric acid uptake appeared not due to increased passive permeation (estimated with l-glucose) or to increased α-aminoisobutyric acid efflux. When short uptake assay times were employed a depression of α-aminoisobutyric acid influx was observed in toxin-treated hepatocytes. The depression of α-aminoisobutyric acid influx was correlated with a rapid increase in intracellular Na+ (estimated using 22Na+) apparently effected by membrane damage. In contrast, the uptake of cycloleucine in the presence of unlabeled α-aminoisobutyric acid (assay for Na+-independent amino acid uptake) by hepatocytes treated with toxin for 5 min was decreased to only a small extent or not at all depending upon experimental design. At later times, C. perfringens enterotoxin increased the exodus of l-glucose, 3-O-methylglucose and α-aminoisobutyric acid from pre-loaded cells indicating that the toxin effects progressive membrane damage. When enterotoxin was removed by repeated washing after 5–20 min the decay of α-aminoisobutyric acid uptake ceased and appeared to undergo recovery towards the hormonally induced control level. The degree of recovery of α-aminoisobutyric acid uptake was inverse to the length of time of exposure to toxin. Adding at 10 min specific rabbit antiserum against C. perfringens enterotoxin without medium change also reversed the effect of toxin on increased intracellular 22Na+, and on the exodus (from preloaded cells) of α-aminoisobutyric acid, L-glucose, and 3-O-methylglucose.  相似文献   

14.
Plasmid pIY2 DNA which encodes for ampicillin-resistance was used to study the energetics of Ca++-induced transformation in Escherichia coli. When cells are exposed to DNA in the presence of carbonylcyanide-m-chlorophenylhydrazone or 2,4-dinitrophenol, two protonophores that collapse the proton electrochemical gradient across the cell membrane (ΔμH+), transformation to ampicillin-resistance is drastically reduced with little or no effect on viability. Furthermore, when the components of ΔμH+ are altered by varying ambient pH or by performing transformation in the presence of valinomycin or nigericin, the efficiency of transformation is directly correlated with the magnitude of the membrane potential and changes in the pH gradient have no significant effect. It is concluded that ΔμH+, more specifically the membrane potential, plays a critical role in Ca++-induced transformation.  相似文献   

15.
The Michaelis-Menten parameters, JM and Km of the initial 1-min fluxes of uptake of l-phenylalanine and of α-aminoisobutyric acid were determined for extracellular concentrations of Na+ ranging from 0.5 to 110 mequiv/l for Ehrlich ascites tumor cells. The maximal initial flux, JM, decreased with decrease in extracellular Na+ for both α-aminoisobutyric acid and phenylalanine but the Km for α-aminoisobutyric acid increased markedly as the Na+ concentration fell whereas the Km for phenylalanine decreased. Cycloleucine behaved like phenylalanine.The data provides strong evidence that the Na+-independent flux of phenylalanine is an exchange diffusion flux that can be varied by changing the intracellular level of amino acids such as phenylalanine. For phenylalanine, cyclolcucine, and methionine this exchange diffusion flux appears to be additive with the Na+-dependent initial flux. α-Aminoisobutyric acid also has an exchange diffusion that is Na+-independent but it has a high Km and is not additive with the Na+-dependent flux.  相似文献   

16.
A protein, cesalin, isolated from Caesalpiniagilliesii is cytotoxic to KB cells in tissue culture. It has been shown to bind to the plasma membrane of this cell line and to inhibit Na+, K+-ATPase (ATP phosphohydrolase EC 3.6.1.3). Similar studies with HTC cells show no cytotoxicity or inhibition of plasma membrane Na+, K+-ATPase. The Na+, K+-ATPase of human erythrocytes and rat brain and kidney tissues are not inhibited. 5′-Nucleotidase and Mg++-ATPase are not inhibited by cesalin in any cells tested.  相似文献   

17.
Inhibition of parathyroid hormone (PTH)-sensitive adenylate cyclase by {Nle-8, Nle-18, Tyr-34} bPTH-(3–34) amide was studied in thyroparathyroid-ectomized dogs. The inhibitory effect was shown to be markedly enhanced by the addition of calcium ions into the in, vitro assay system. At 0.1 mM Ca2+, complete inhibition by the antagonist was obtained. Chelation of exogenous Ca2+ by EGTA eliminated the Ca2+-induced inhibition. Both the basal and hormone-stimulated activities were decreased in the presence of 0.1 mM Ca2+, whereas the addition of EGTA increased both activities. Our results suggest that Ca2+ modulates canine renal PTH-sensitive adenylate cyclase and its inhibition by substituted bPTH-(3–34).  相似文献   

18.
Mitochondria isolated from rat heart and kidney cortex by Polytron treatment of the tissues exhibit lower state 3 rates of respiration than mitochondria isolated by Nagarse method. Addition of cytochrome c to Polytron mitochondria isolated from heart, but not from kidney, increases oxygen uptake to values approaching those of Nagarse-treated preparations. Similar results were observed for Ca2+ uptake. Kidney Polytron mitochondria exhibited lower mitochondrial, but higher non-mitochondrial enzyme activities compared to kidney Nagarse mitochondria. Enzyme activities were the same in Polytron and Nagarse mitochondria from heart. The differences between Polytron and Nagarse mitochondria appear to be mainly due to lower cytochrome c content of Polytron mitochondria from heart and higher contamination of Polytron mitochondria from kidney.  相似文献   

19.
Effect of in vivo oxygenation on mitochondrial respiratory chain capacity was studied in newborn puppies. Heart mitochondria were isolated from 0 to 7 days. As the arterial PO2 rises sharply during the first 3–4 days, State 3 respiratory capacity and Ca++ transport activity decrease linearly. Cytochrome c and a + a3 concentrations increase rapidly. Thus the enzymatic turnover of the respiratory chain decreases to one-fifth of the fetal term value in 4 days. These data are in agreement with earlier results indicating a strong controlling effect of in vivo oxygenation on mitochondrial respiratory capacity.  相似文献   

20.
J Fukuda  K Kawa 《Life sciences》1977,21(7):981-988
Skeletal muscle fibers of beetle larvae, Xylotrupesdichotomus L., which were inexcitable in the standard saline solution at pH 7.4 became capable of generating all-or-none spikes when a certain amount of acetate was added to a low pH saline solution. The optimum condition for the spike initiation was the presence of 20–30 mM acetate at pH 6. The spikes thus elicited were pure Ca-spikes as they were dependent on the external Ca++ concentration but were not inhibited either by removal of the external Na+ or by application of tetrodotoxin. This facilitation of the Ca-spike generation was probably due to a combined action of acetate and of the low pH upon the muscle membrane.  相似文献   

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