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1.
The ionic dependency and transmission of epidermal action potentials have been examined from tailbud to hatching stages of newt embryos. Previously we have reported that the epidermal action potential is composed of a fast- and slow-action component; only the slow-action component, however, is transmitted to other cells. We address in this report the mechanism by which these responses are mediated. The slow-action potential is not produced in Na+-free saline, tricaine saline, or following the application of TTX, and thus appears to be Na+ dependent. The fast-action potential on the other hand is blocked by application of Co2+ and verapamil saline and thus appears to be Ca2+ dependent. The slow-action potentials appear to be chemically transmitted since they are transmitted even to those cells which are electrically uncoupled at low intracellular pH (NaHCO3 + HCl, pH 6.2). Furthermore 1 μM curare and atropine are inhibitory to transmission of the slow potential. Epidermal cells of the newt embryo are sensitive to acetylcholine (ACh) applied by hydrostatic ejection through a micropipet. The latter observation further suggests that propagation of the slow-action potential is, in part, a chemical event.  相似文献   

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The action of mutations affecting the epicuticular wax of Pisum sativum has been investigated at the chemical and ultrastructural level. Upper and lower surfaces of the leaves were found to differ markedly in both ultrastructure and chemistry. Mutations affected primarily either the lower (wa, wb and wsp) or the upper surface (wlo), but some effects of all 4 genes could be seen on both surfaces. Specific biochemical lesions could be implied for wsp and wa but the chemical effects of wb and wlo were more diffuse. Generally a close relation between chemical composition and crystallite form of the wax was evident throughout the work.  相似文献   

4.
The effects of several factors that affect the sugar transport activity in rat epididymal fat cells were studied. The transport activity was assessed semiquantitatively by measuring the uptake of 3-O-methyl-d-glucose by the oil-flotation method. The transport activity was stimulated by mechanical agitation, such as centrifugation of cells. This effect was transient. When agitated cells were incubated at 37 °C with gentle shaking, their transport activity declined. The decline was often facilitated by the addition of glucose or pyruvate. Presumably some cell preparations were low in the source of metabolic energy that was required for this recovery process. When cells were exposed to a high concentration of insulin, washed, and suspended in fresh buffer, the effect of insulin (plus that of mechanical agitation) declined after a certain lag period. The length of this period was a function of the initial insulin concentration. The incubation temperature had different effects on the basal and plus-insulin activities. The basal activity at 25 °C was higher than that at 37 °C, while the plus-insulin activity was lower at 25 °C than at 37 °C.  相似文献   

5.
Three calcium (Ca) antagonists and dipyridamole were examined in the isolated perfused guinea pig heart at perfusate Ca concentrations of 1.25 and 3.75 mM. The Ca antagonists: FR 7534, nifedipine and D600 produced similar dose-dependent decreases in left ventricular dp/dt and myocardial oxygen consumption (MV?O2) at both Ca concentrations. However, dose response curves were shifted significantly to the right by increased perfusate Ca requiring six to ten times more Ca antagonist to produce equivalent effects. Dipyridamole produced only slight negative inotropic effects which appeared to be less dependent on external Ca concentration. All four agents significantly increased coronary blood flow at 1.25 mM Ca but not at 3.75 mM Ca. The Ca antagonists decreased heart rate at 3.75 mM Ca whereas dipyridamole had strong negative chronotropic effects at both perfusate Ca concentrations. These experiments provide evidence that FR 7534 acts as a Ca antagonist. In addition, Ca antagonists of different structure had similar effects on the isolated heart distinct from those of dipyridamole.  相似文献   

6.
In vitro radioligand binding and autoradiographic distribution studies have suggested the possible involvement of central sigma-opiate sites in the effects of several purportedly dopaminergic agents. Specifically, Largent et al. (Proc. Nat. Acad. Sci. 81, 4983, 1984) proposed that "actions of 3-PPP at sigma receptors may account for the effect of the drug on behavior and dopaminergic nerve function". Using the sigma-opiate- and dopamine (DA)-preferring (-)- and (+)-enantiomer, respectively, of butaclamol, and the two enantiomers of 3-PPP, the present study was undertaken to address the in vivo functional significance of this proposal. To this end we investigated various biological responses considered to reflect drug interactions with DA cell body and terminal autoreceptors and with presumed non-synaptic and postsynaptic DA receptors in the rat CNS. (+)- but not (-)-butaclamol antagonized the 3-PPP (either enantiomer)-induced DA synthesis and prolactin decreases in GBL-treated rats, the (+)-3-PPP-induced inhibition of substantia nigra DA cell firing and the (+)-3-PPP-induced reversal of reserpine akinesia. Taken together with previous findings available data suggest that DA rather than sigma-opiate receptors mediate the neurochemical, electrophysiological, behavioral and other physiological (prolactin, body temperature) effects of 3-PPP and its enantiomers. The in vivo pharmacological relevance of the claimed non-dopaminergic, proposedly sigma-opiatergic, radioligand binding demonstrated in vitro (with e.g. (+)-3-PPP) thus remains to be established.  相似文献   

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Enzymes of glutamate metabolism were studied in the astrocytes isolated from rats injected with a large dose of ammonium acetate and compared with those isolated from controls. The activities of glutamate dehydrogenase (GDH) and glutaminase decreased while those of glutamine synthetase (GS) and aspartate aminotransferase (AAT) increased both in convulsive and comatose states. The activity of alanine aminotransferase (A1AT) increased only in convulsive state. The results suggested that glutamate required for the formation of glutamine in astrocytes might have its origin in nerve endings and the depletion of citric acid cycle intermediates might occur in nerve endings at least in acute ammonia toxicity.  相似文献   

9.
The Bio 14.6 hamster has a well-documented cardiomyopathy which leads to congestive heart failure. Previous work demonstrated that hearts from these hamsters have depressed fatty acid oxidation and depressed carnitine concentrations compared to those of normal hamsters. Analyses of tissue carnitine concentrations from 40 to 464 days of age demonstrate that the cardiomyopathic hamsters have a cardiac carnitine deficiency throughout life. Therefore, the carnitine deficiency is not a secondary effect of an advanced stage of the cardiomyopathy. Both the observation that other tissues of the cardiomyopathic hamster have normal or markedly elevated carnitine concentrations and the observation that oral carnitine treatment could not increase the cardiac carnitine concentrations to those of normal hamsters are consistent with the hypothesis that the cardiac carnitine deficiency is the result of a defective cardiac transport mechanism. Cardiac carnitine-binding protein (which may function in the cardiac carnitine transport mechanism) prepared from hearts of cardiomyopathic hamsters had a lower maximal carnitine binding and an increased dissociation constant for carnitine compared to the cardiac carnitine-binding protein prepared from normal hamsters. Thus, several types of data indicate that the cardiomyopathic hamster has an altered cardiac carnitine transport mechanism.  相似文献   

10.
The effect of oleate, palmitate, and octanoate on glucose formation was studied with lactate or pyruvate as substrate. Octanoate was much more quickly oxidized and utilized for ketone body production than were oleate and palmitate. Among fatty acids studied, only octanoate resulted in a marked increase of the 3-hydroxybutyrate/acetoacetate (3-OHBAcAc) ratio. Each of the fatty acids studied stimulated glucose synthesis from pyruvate. The enhancement of gluconeogenesis by long-chain fatty acids was abolished after the addition of ammonia. As concluded from the “crossover” plot, the stimulatory effect of fatty acids was due to: (i) a stimulation of pyruvate carboxylation, (ii) a provision of reducing equivalents for glyceraldehyde phosphate dehydrogenase, and (iii) an acceleration of flux through hexose diphosphatase. Moreover, palmitate and oleate resulted in an increased generation of mitochondrial phosphpenolpyruvate, while in the presence of octanoate, the activity of mitochondrial phosphoenolpyruvate carboxykinase was diminished. When lactate was used as the glucose precursor, palmitate and oleate increased glucose production by about 50% but did not affect the contribution of mitochondrial phosphoenolpyruvate carboxykinase to gluconeogenesis. In contrast, in spite of the stimulation of both pyruvate carboxylase and hexose diphosphatase, as judged from the crossover plot, the addition of octanoate resulted in a marked inhibition of both glucose formation and mitochondrial generation of phosphoenolpyruvate. The inhibitory effect of octanoate was reversed by ammonia. Results indicate that fatty acids and ammonia are potent regulatory factors of both the rate of glucose formation and the contribution of mitochondrial phosphoenolpyruvate carboxykinase to gluconeogenesis in hepatocytes of the fasted rabbit.  相似文献   

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Candida albicans cells grown on alkanes of different chain lengths (C13, C14, C15, C16, C17, and C18) exhibited a low growth rate and gradual increase in the total lipid content with the increase in the length of alkanes. There was a significant change in the phospholipids and sterols content of various alkane-grown cells compared to glucose-grown cells. In glucose-grown cells, the transport of various amino acids, e.g., proline, glutamic acid, lysine, glycine, phenylalanine, serine, methionine, and leucine was found to be energy dependent and against a concentration gradient. In alkane-grown cells, the transport of lysine, proline, serine, and methionine was reduced, however, there was no effect on the uptake of glycine, glutamic acid, phenylalanine, and leucine. The results were interpreted as different carrier(s) responsible for amino acid uptake responsed differently to the change of lipid environment.  相似文献   

14.
A mute isoenzyme of type II cAMP-dependent protein kinase from rat muscle has been reported that is released from the regulatory subunit by cAMP but remains inactive until combination with heat- and acid-stable modulator has occurred. This enzyme has now been obtained in isolation free of the normal catalytic subunit using affinity chromatography with both an ATP analog (Blue Dextran/Sepharose) and a protein substrate analog (Kemptide/CH-Sepharose). Separation can be effected in both cases before activation of the mute enzyme. Affinity of the mute enzyme for Blue Dextran--a ligand specific for the dinucleotide fold in this kinase--is somewhat higher than that of the normal enzyme. Conversely, before reaction with the modulatory protein the mute enzyme will not bind at all to Kemptide/CH-Sepharose, where the normal enzyme elutes at 50 mM KCl. When pretreated with the modulatory protein and so activated, mute enzyme binds to Kemptide with a very high affinity and can only be eluted using a natural substrate (phosphorylase kinase), up to 500 mM salt being ineffective. The modulator thus appears to act through alteration of the protein substrate binding site on the enzyme.  相似文献   

15.
Addition of nifurtimox (a nitrofuran derivative used for the treatment of Chagas' disease) to rat liver microsomes produced an increase of (a) electron flow from NADPH to molecular oxygen, (b) generation of both superoxide anion radical (O2?) and hydrogen peroxide, and (c) lipid peroxidation. The nifurtimox-stimulated NADPH oxidation was greatly inhibited by NADP+ and p-chloromercuribenzoate, and to a lesser extent by SKF-525-A and metyrapone. These inhibitions reveal the function of both the NADPH-cytochrome P-450 (c) reductase and cytochrome P-450 in nifurtimox reduction. Superoxide dismutase, catalase (in the presence of superoxide dismutase), and hydroxyl radical scavengers (mannitol, 5,5-dimethyl-1-pyrroline-1-oxide) inhibited the nifurtimox-stimulated NADPH oxidation, in accordance with the additional operation of a reaction chain including the hydroxyl radical. Further evidence supporting the role of superoxide anion and hydroxyl radicals in the nifurtimox-induced NADPH oxidation resulted from the effect of specific inhibitors on NADPH oxidation by O2? (generated by the xanthine oxidase reaction) and by OH. (generated by an iron chelate or the Fenton reaction). Production of O2? by rat kidney, testes and brain microsomes was significantly stimulated by nifurtimox in the presence of NADPH. It is postulated that enhanced formation of free radicals is the basis for nifurtimox toxicity in mammals, in good agreement with the postulated mechanism of the trypanocide effect of nifurtimox on Trypanosoma cruzi.  相似文献   

16.
Palmitoyl CoA (PCoA) and the adenine translocase inhibitor atractyloside (ATR) appear to produce a similar effect in discharging accumulated calcium from cardiac mitochondria. Although mitochondrial respiration is stimulated upon addition of either PCoA or ATR to preparations preloaded with calcium, the effect is not the same as that produced by classical uncouplers. PCoA and ATR also do not interfere with respiration-supported calcium uptake by mitochondria. The presence of exogenous ATP can prevent the calcium discharging effects of PCoA or ATR. Carnitine will prevent the PCoA calcium discharging effect, but has no effect on ATR-induced discharge. It is suggested the PCoA may act at a site on or near the adenine translocase, perhaps through allosteric interaction, to produce an efflux of calcium from mitochondria. The results also suggest that the internal adenine nucleotide pool plays a significant role in mitochondrial calcium retention.  相似文献   

17.
Collagenase digestion of minced lung tissue yielded isolated cells, functionally viable as judged by several metabolic and morphological criteria, representative of all the cell species normally present in the tissue. The efficiency of the isolation procedure was about 25 per cent. Aerobic metabolism was not affected by most of the substrates tested except by succinate which increased oxygen utilization, and glucose, fructose and octanoate which significantly decreased oxygen uptake. Since no significant changes have been observed in the cellular adenine nucleotide content during glucose depression of aerobic metabolism it is concluded that the glycolytic flux had to be sufficient as to account for the decrease in the mitochondrial energy production. The mechanism responsible for these effects as well as their physiological significance are discussed herewith.  相似文献   

18.
The metabolism of 2-bromoethylaminonaphthoquinone in hepatocytes isolated from rats was studied. This compound was chemically inert in the reaction system used. However, in buffer solution containing isolated hepatocytes, it was gradually converted into aziridinylnaphthoquinone. Under the same reaction conditions, 4-chlorobutylaminonaphthoquinone also gave the cyclization products, pyrrolidinylnaphthoquinone. Cellular GSH decreased in both reactions.  相似文献   

19.
A comparative study of the effect of misonidazole and novel radiosensitizers on glutathione (GSH) levels and related enzyme activities in isolated rat hepatocytes was performed. Incubation of hepatocytes with 5 mM radiosensitizers led to a decrease in the intracellular GSH level. The most pronounced decrease in cellular GSH was evoked by 2,4-dinitroimidazole-1-ethanol (DNIE); after incubation for only 15 min, GSH was hardly detected. DNIE-mediated GSH loss was dependent upon its concentration. DNIE reacted with GSH nonenzymatically as well as with diethylmaleate, while misonidazole and 1-methyl-2-methyl-sulfinyl-5-methoxycarbonylimidazole (KIH-3) did not. Addition of partially purified glutathione S-transferase (GST) did not enhance DNIE-mediated GSH loss in a cell-free system. DNIE inhibited glutathione peroxidase (GSH-Px), GST, and glutathione reductase (GSSG-R) activities in hepatocytes, while misonidazole and KIH-3 did not. GSH-Px activity assayed with H2O2 as substrate was the most inhibited. Inhibition of GSH-Px activity assayed with cumene hydroperoxide as substrate and GST was less than that of GSH-Px assayed with H2O2 as substrate. GSSG-R activity was decreased by DNIE, but not significantly. Incubation of purified GSH-Px with DNIE resulted in a little change in the activity when assayed with H2O2 as substrate.  相似文献   

20.
The template activity of isolated rat liver nuclei for DNA synthesis assayed with E.coli DNA polymerase was found to be dependent upon the presence of Ca2+ or Mg2+ in the incubation medium. DNA was prepared from isolated nuclei subjected to conditions which activated the template and centrifuged in an alkaline sucrose gradient. The distribution profile showed that smaller fragments were formed, suggesting enhancement of endonucleolytic activity. When isolated nuclei were incubated with NAD to induce poly(adenosine diphosphate ribose) formation and were subjected to the activation conditions, the template for DNA synthesis remained unchanged. The distribution profile in an alkaline sucrose gradient of DNA prepared from these nuclei and control nuclei was identical. The present findings suggest that the template-activating system for DNA synthesis was blocked when isolated nuclei were treated with NAD invitro.  相似文献   

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