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1.
BIOCHEMICAL AND ULTRASTRUCTURAL ASPECTS OF CA2+ TRANSPORT BY MITOCHONDRIA OF THE HEPATOPANCREAS OF THE BLUE CRAB CALLINECTES SAPIDUS 总被引:1,自引:1,他引:0
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Chung-Ho Chen John W. Greenawalt Albert L. Lehninger 《The Journal of cell biology》1974,61(2):301-315
Mitochondria isolated from the hepatopancreas of the blue crab Callinectes sapidus show up to 12-fold stimulation of respiration on addition of Ca2+, which is accompanied by Ca2+ accumulation (Ca2+:site = 1.9) and H+ ejection (H+:Ca2+ = 0.85). Sr2+ and Mn2+ are also accumulated; Mg2+ is not. A strongly hypertonic medium (383 mosM), Mg2+, and phosphate are required for maximal Ca2+ uptake. Ca2+ uptake takes precedence over oxidative phosphorylation of ADP for respiratory energy. Once Ca2+ is accumulated by the crab mitochondria, it is stable and only very slowly released, even by uncoupling agents. ATP hydrolysis also supports Ca2+ uptake. Respiration-inhibited crab hepatopancreas mitochondria show both high-affinity and low-affinity Ca2+-binding sites, which are inactive in the presence of uncoupling agents. Crab hepatopancreas mitochondria have an enormous capacity for accumulation of Ca2+, up to 5,500 ng-atoms Ca2+ per mg protein, with an equivalent amount of phosphate. Freshly isolated mitochondria contain very large amounts of Ca2+, Mg2+, phosphate, K+, and Na+; their high Ca2+ content is a reflection of the vary large amount of extra-mitochondrial Ca2+ in the whole tissue. Electron microscopy of crab mitochondria loaded with Ca2+ and phosphate showed large electron-dense deposits, presumably of precipitated calcium phosphate. They consisted of bundles of needle-like crystals, whereas Ca2+-loaded rat liver mitochondria show only amorphous deposits of calcium phosphate under similar conditions. The very pronounced capacity of crab hepatopancreas mitochondria for transport of Ca2+ appears to be adapted to a role in the storage and release of Ca2+ during the molting cycle of this crustacean. 相似文献
2.
EFFECT OF ACTIVE ACCUMULATION OF CALCIUM AND PHOSPHATE IONS ON THE STRUCTURE OF RAT LIVER MITOCHONDRIA 总被引:28,自引:11,他引:17
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Rat liver mitochondria allowed to accumulate maximal amounts of Ca++ and HPO4= ions from the suspending medium in vitro during respiration have a considerably higher specific gravity than normal mitochondria and may be easily separated from the latter by isopycnic centrifugation in density gradients of sucrose or cesium chloride. When the mitochondria are allowed to accumulate less than maximal amounts of Ca++ and HPO4= from the medium, they have intermediate specific gravities which are roughly proportional to their content of calcium phosphate. Maximally "loaded" mitochondria are relatively homogeneous with respect to specific gravity. Correlated biochemical and electron microscopic studies show that Ca++-loaded mitochondria contain numerous dense granules, of which some 85 per cent are over 500 A in diameter. These granules are electron-opaque not only following fixation and staining with heavy metal reagents, but also following fixation with formaldehyde, demonstrating that the characteristic granules in Ca++-loaded mitochondria have intrinsic electron-opacity. The dense granules are almost always located within the inner compartment of the mitochondria and not in the space between the inner and outer membranes. They are frequently located at or near the cristae and they often show electron-transparent "cores." Such granules appear to be made up of clusters of smaller dense particles, but preliminary x-ray diffraction analysis and electron diffraction studies have revealed no evidence of crystallinity in the deposits. The electron-opaque granules decrease in number when the Ca++-loaded mitochondria are incubated with 2,4-dinitrophenol; simultaneously there is discharge of Ca++ and phosphate from the mitochondria into the medium. 相似文献
3.
Abstract— The incubation of brain stem slices from adult rats in a K+-enriched medium containing a 5-HT uptake inhibitor (fluoxetine) significantly increased their capacity to synthesize 5-HT from tryptophan. The K+-induced stimulation of 5-HT synthesis was at least partly dependent on the depletion of the indoleamine in tissues since: (1) a good correlation was found between the respective changes in 5-HT release and synthesis evoked by high K+ concentrations in the presence of various 5-HT uptake inhibitors; (2) the modifications in endogenous 5-HT levels produced by in vim treatments with drugs (reserpine, pargyline) or by incubating slices with 5-HT altered the stimulating effect of high K+ concentrations and fluoxetine on 5-HT synthesis; (3) the replacement of Ca2+ by Co2+ (4 mM) or EGTA (0.1 mM) in the incubating medium completely prevented the increased 5-HT release and synthesis evoked by high K+ concentrations and fluoxetine. The extraction of tryptophan hydroxylase from incubated tissues revealed that the increased 5-HT synthesis occurring in K+-enriched medium was associated with an activation of this enzyme. Kinetic analyses indicated that this activation resulted from an increase in the Vmax of tryptophan hydroxylase, its apparent affinities for both tryptophan and 6-MPH4 being not significantly affected. In contrast to the tryptophan hydroxylase from tissues incubated in normal physiological medium, the activated enzyme from tissues depolarized by K+ was hardly stimulated by Ca2+-mediated phosphorylating conditions. This led to the proposition of a hypothetical model by which the Ca2+ influx produced by the neuronal depolarization would trigger the activity of a Ca2+-dependent protein kinase capable of activating tryptophan hydroxylase. Although this sequence is still largely speculative it must be emphasized that, as expected from such a model, the regional differences in the K+-evoked activation of tryptophan hydroxylase in slices (cerebral cortex > brain stem > spinal cord) were parallel to those of the Ca2+-dependent protein phosphorylation (r= 0.92) and those of the activating effect of phosphorylating conditions on soluble tryptophan hydroxylase (r= 0.96). 相似文献
4.
M H Freedman 《Cellular immunology》1979,44(2):290-313
45Ca2+ uptake was detected within minutes following addition of T- and B-cell2 mitogens to mouse lymphocytes. The T-cell mitogens (Con A and PHA) gave an ~twofold increase in 45Ca2+ uptake (representing an influx of ~ 130 amol per lymphocyte, corresponding to an increase in average cellular Ca2+ of ~0.95 mM). B-cell mitogens which gave the largest 45Ca2+ uptake (~twofold) were purified LPS preparations from Salmonella minnesota R595 and Escherichia coli 0111:2125. The 45Ca2+ uptake by rabbit splenocytes using specific anti-b4 allotype antiserum was comparable to that obtained with the two purified LPS preparations. A23187, in low nontoxic doses, gave an ~sixfold increase in 45Ca2+ uptake with mouse T cells. The 45Ca2+ uptake was modulated by cyclic nucleotides showing a “yin-yang” effect. The results suggest a possible entry of 45Ca2+ from the extracellular medium through “gated Ca2+ channels” in the plasma membrane into the cytosol by passive diffusion. The Ca2+ may be sequestered in the mitochondria, and the excess Ca2+ is later effluxed into the extracellular medium. The fact that 45Ca2+ uptake appears to be one of the earliest events occurring after ligand binding to the cell, together with the demonstration of a Ca2+-dependent glucose uptake and a requirement for extracellular Ca2+ for DNA synthesis, suggest that, as it is now known to function in many other cellular responses, Ca2+ may operate as a second messenger for lymphocyte activation. 相似文献
5.
Previous investigators have shown that following doxorubicin treatment heart mitochondria appear swollen and contain intramitochondrial dense inclusion bodies identified as calcium phosphate. In vitro studies have shown that similar morphological changes occur in mitochondria previously loaded with excess calcium. The present studies were performed to determine the effects of doxorubicin and its aglycone metabolite on 45Ca2+ uptake by mitochondria isolated from the heart, liver, and kidney of the rabbit. Doxorubicin (100 μM) significantly inhibited the initial rate of 45Ca2+ accumulated by mitochondria isolated from the three tissues. In contrast, the aglycone metabolite (100 μM) induced the reverse effect. In preloaded mitochondria the aglycone stimulated the release of calcium while doxorubicin was without effect. Mitochondria from the heart were significantly more sensitive to the effects of these anthracyclines than were mitochondria from the other two tissues. If these in vitro effects also occur in vitro, then the aglycone metabolite would be a more likely candidate in explaining the morphological changes in heart mitochondria previously described. 相似文献
6.
Calcium Uptake and Catecholamine Secretion by Cultured Bovine Adrenal Medulla Cells 总被引:20,自引:8,他引:12
Daniel L. Kilpatrick Ruta J. Slepetis James J. Corcoran Norman Kirshner 《Journal of neurochemistry》1982,38(2):427-435
Abstract: The uptake of 45Ca2+ and secretion of catecholamines by primary cultures of adrenal medulla cells were studied. Nicotine, veratridine, potassium, and Ionomycin stimulate both the accumulation of 45Ca2+ and the secretion of catecholamines. Nicotinic antagonists block 45Ca2+ uptake induced by nicotine, tetrodotoxin blocks 45Ca2+ uptake induced by veratridine, and D600 blocks uptake induced by K+, nicotine, and veratridine, but not 45Ca2+ uptake or secretion induced by Ionomycin. The EC50 for nicotine is 3 μm for catecholamine secretion and 10 μm for 45Ca2+ uptake, while the EC50S for veratridinestimulated uptake and secretion are approximately the same (75 μm ). Kinetic studies show that the uptake of Ca2+ is rapid and appears to precede the secretion of catecholamines, and that the rate of uptake declines rapidly. The uptake of 45Ca2+ and secretion of catecholamines stimulated by veratridine and 50 mm -K+ show saturation kinetics with respect to external calcium concentrations at about 2 mm . On the other hand, the uptake of 45 Ca2+ stimulated by nicotine does not become saturated at external calcium concentrations of 10 mm although the secretion of catecholamines reaches a maximum at external calcium concentrations of 2 mm . The data suggest that depolarizing agents such as veratridine and 50 mm -K+ stimulate 45Ca2+ entry through voltage-sensitive calcium channels, while nicotinic agonists stimulate calcium entry through the acetylcholine receptor ion channels as well as through voltage-sensitive calcium channels. 相似文献
7.
STUDIES ON THE FIXATION OF ARTIFICIAL AND BACTERIAL DNA PLASMS FOR THE ELECTRON MICROSCOPY OF THIN SECTIONS 总被引:6,自引:1,他引:5
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Werner H. Schreil 《The Journal of cell biology》1964,22(1):1-20
The process of fixation of DNA-containing plasms is investigated by macroscopical and electron microscopical observations on solutions of DNA, nucleohistones, as well as on bacterial nuclei. The following treatments were found to produce a gelation of a solution of DNA or nucleohistones: (a) OsO4 fixation at pH 6 in the presence of amino acids (tryptone) and Ca++. (b) Exposure to aqueous solutions of uranyl acetate. (c) Exposure to aqueous solutions of indium chloride. Observed in the electron microscope, these gels show a fine fibrillar material. From experiments in which solutions of DNA or nucleohistones are mixed with bacteria and treated together, it is concluded that the behavior of the bacterial nucleoplasm is similar to that of the DNA solutions. The appearance of birefringence indicates that uranyl acetate and indium chloride produce an orientation of the molecules of a DNA solution during gelation. Bacterial chromosomes fixed by these agents also show a certain order, while those fixed by the OsO4-amino acid-Ca++ formula do not. Whether or not the order can be considered to be artificial is discussed, and a tentative conclusion is presented: (a) Uranyl acetate may induce artificial order. (b) Fixatives which do not gel DNA probably result in the grossest artifacts. (c) OsO4 fixation at pH 6 in the presence of amino acids (tryptone) and Ca++ may give the most accurate preservation of the in vivo disposition of DNA (RK+ fixation). 相似文献
8.
《Journal of steroid biochemistry》1982,16(6):591-597
In the previous paper (J. steroid Biochem. 16 (1982) 437–446. [5]), we demonstrated that in vitro liver microsomal preparations of adult male rats possessed binding sites specific for progesterone (Prog) 2 of high affinity (KD ∼ 25.2 nM) and high capacity (Nmax ∼ 6.43 pmol/mg of microsomal protein), using 130 mM NaCl-based incubation buffer. To explore the biological roles of liver microsomal Prog binding, we investigated the effects of such binding on liver microsomal Ca2+ pump activity. Firstly, we obtained results similar to those previously obtained concerning the characteristics of microsomal Prog binding using 100 mM KCl-based incubation buffer, usually used for experiments on microsomal Ca2+ pump activity. For microsomal 45Ca2+ uptake we also obtained results similar to those already demonstrated by several investigators. That is to say liver microsomal 45Ca2+ uptake was markedly increased by the addition of 30 mM oxalate and 5 mM ATP, and was not inhibited by the addition of 5 mM NaN3 into the incubation buffer. However, the addition of 1.0 μM Prog, as well as 17β-hydroxy-5α-androstan-3-one (5α-DHT) and estradiol-17β (E2 -17β), which should be a sufficiently saturable concentration for liver microsomal binding sites specific for it, affected little microsomal 45Ca2+ uptake statistically, though microsomal binding capacity for Prog was 5–10 times higher than that for 5α-DHT and E2-17β. In addition, Prog (1.0 μM) had little effect on 45Ca2+ release from prelabeled microsomes. In conclusion, we suggest, therefore, that there is no direct correlation between binding of sex hormones and Ca2+ pump activity by rat liver microsomal preparations. 相似文献
9.
Darrell J. Leier Richard A. Jungmann 《Biochimica et Biophysica Acta (BBA)/General Subjects》1973,329(2):196-210
The effect of adrenocorticotropic hormone and dibutyryl cyclic AMP on the uptake of 45Ca2+ by the rat adrenal gland has been investigated. After injection of 45Ca2+ and adrenocorticotropic hormone into rats, the adrenal 45Ca2+ concentration was significantly enhanced 90 to 180 min following hormone administration. The rise in adrenal 45Ca2+ content was accompanied by a marked increase of the serum corticosterone levels. During incubation of rat adrenal glands in the presence of 45Ca2+, adrenocorticotropic hormone and dibutyryl cyclic AMP caused significant accumulation of adrenal 45Ca2+ and increased corticosterone synthesis. The degree of stimulation of both adrenal 45Ca2+ uptake and corticosterone synthesis by adrenocorticotropic hormone or dibutyryl cyclic AMP was dependent upon the concentration of calcium in the incubation medium and upon the amount of adrenocorticotropic hormone or dibutyryl cyclic AMP added. Theophylline mimicked the stimulatory effect of adrenocorticotropic hormone and dibutyryl cyclic AMP and increased the uptake of 45Ca2+ by rat adrenal glands in vitro. Determination of calcium by atomic absorption spectroscopy showed that the adrenocorticotropic hormone-mediated adrenal 45Ca2+ uptake was due to a net accumulation of calcium in the tissue and not only to an increased rate of exchange of extracellular 45Ca2+ with the intracellular calcium pool. Adrenocorticotropic hormone-stimulated adrenal 45Ca2+ uptake was not observed when steroidogenesis was inhibited with elipten. Both adrenocorticotropic hormone-mediated corticosterone synthesis and adrenal 45Ca2+ uptake were abolished after treatment of rats with cycloheximide but not after treatment with actinomycin D, indicating that adrenal 45Ca2+ uptake and steroidogenesis have similar requirements for de novo protein synthesis, but not RNA synthesis. 相似文献
10.
The ability of microsomal preparations to transport 45Ca2+ was studied in preparations of control and secretagogue-stimulated pancreatic acini. ATP-dependent 45Ca2+ uptake activity was present in the pancreatic post-mitochondrial supernatant and microsomes but little activity was present in the postmicrosomal supernatant. Treatment of acini with the secretagogues cholecystokinin (CCK) and carbamylcholine (CCh) prior to cell fractionation increased the subsequently measured microsomal 45Ca2+ uptake. The effect of CCK was maximal after 10 min stimulation and at a not. The effect of CCK was maximal after 10 min stimulation and at a concentration of 1 nM; these conditions are comparable to the effects of CCK on 45Ca2+ fluxes in intact acini. The increased microsomal 45Ca2+ uptake induced by CCK was due to an increase in the maximal rate of 45Ca2+ uptake as there was no effect on the Km for Ca2+ (1 μM). It is concluded that secretagogues increase the ATP-dependent uptake of 45Ca2+ by an isolated pancreatic microsomal component under the same conditions that also stimulate both digestive enzyme secretion and bi-directional Ca2+ movements. 相似文献
11.
N. S. Rustum Maluf 《The Journal of general physiology》1940,24(2):151-167
1. Reasons are given for believing that the uptake of Na+, Cl-, and NaCl by the crayfish occurs through the gills. 2. A crayfish in fresh water, with a Cl concentration of about 0.2 mEq./l., can) by active Cl absorption, compensate entirely for Cl lost in the urine. 3. The carbonic anhydrase activity of the gills is markedly higher than that of other tissues of the crayfish, but the equivalent CO2 output of the crayfish is far in excess of the equivalent Cl absorption per unit time and weight and thus fails to warrant the supposition that Cl absorption is of respiratory importance. 4. The carbonic anhydrase activity of the soft integument of the lobster, before and after molting, and of the hypodermis of the hard-cuticled animal is almost identical and of the same order as that of other tissues of the lobster. 5. The concentration of the electrolytes was about 7.5 mEq./l.; i.e., considerably lower than in the blood of the crayfish. Cl- can be taken up independently of the complementary cation. Na+ can be taken up independently of the complementary anion. K+ and SO4
= are not taken up at all. In pure NaCl, the Na+ and Cl- are absorbed evidently largely together. Ca++ is absorbed only in newly molted animals and in animals preparing to molt but is not absorbed by hard-cuticled animals not preparing to molt. Ca++ is taken up independently of Cl- in pure CaCl2. 6. Newly molted animals absorb Ca++ at a rate exceeding that of the absorption of other absorbable ions (Na+ and Cl-) in the same equivalent concentration. 7. A crayfish utilizes the Ca++ in fresh water in the calcification of its cuticle. Since the animal does not swallow water, the Ca++ must enter through the exterior. Reasons are given for believing that, unlike Na+ and Cl-, Ca++ is absorbed directly from the exterior by the integument and does not enter the body through the gills. 8. During molting, only about 4 per cent of the raw ash and 2.3 per cent of the organic material of the old cuticle is resorbed. 相似文献
12.
《Insect Biochemistry》1990,20(1):83-89
Isolated tick salivary glands, permeabilized with digitonin in the presence of the Ca2+ uptake inhibitors, sodium azide and vanadate, released Ca2+ in response to 20 μM inositol-1,4,5-trisphosphate (IP3). Inositol-1-phosphate (IP1) and inositol-1,4-bisphosphate (IP2) appeared to stimulate an uptake of Ca2+ into whole glands. Inositol-1,4,5-trisphosphate caused release of Ca2+ from a 100,000 g microsome enriched pellet; however, IP1 and IP2 were ineffective in stimulating an uptake or efflux of Ca2+. The combined 900 and 11,500 g pellets showed no significant release of Ca2+ in response to addition of IP3. Inositol-1,4,5-trisphosphate concentrations as low as 1 μM are capable of stimulating a significant release of Ca2+ from microsomes. Results suggest that intracellular Ca2+ is mobilized from microsomal intracellular stores in response to agonists which increase cytosolic IP3 in tick salivary glands. Results also suggest a possible role for IP1 and IP2 or both in stimulating an uptake of Ca2+ into vanadate and azide-insensitive intracellular pools. 相似文献
13.
The in vivo uptake of 45Ca by certain areas of the rat brain and by the pituitary gland was investigated under normal conditions and in states of cold stress. The uptake of 45Ca was highest in the pituitary gland followed in decreasing order by the superior colliculus, medulla, cerebellum, thalamus, hippocampus and the cortex. Cold stress conditions induced an increase in uptake of 45Ca in the cortex, hippocampus, cerebellum, medulla and the pituitary gland. Our findings suggest that cold stress induces a change in the permeability for calcium in blood-brain and blood-pituitary barriers. 相似文献
14.
W. J. V. Osterhout 《The Journal of general physiology》1940,23(6):749-751
Guaiacol was applied at two spots on the same cell of Nitella. At one spot it was dissolved in 0.01 M NaCl, at the other in 0.01 M CaCl2 or BaCl2. The effect was practically the same in all cases, i.e. a similar change of P.D. in a negative direction, involving a more or less complete loss of P.D. (depolarization). When hexylresorcinol was used in place of guaiacol the result was similar. That Ca++ and Ba++ do not inhibit the effect of these organic depolarizing substances may be due to a lack of penetration of Ca++ and Ba++. The organic substances penetrate more rapidly and their effect is chiefly on the inner protoplasmic surface which is the principal seat of the P.D. 相似文献
15.
Ten phenolic compounds were examined for their effect on mung bean (Phaseolus aureus L.) hypocotyl growth and on respiration and coupling parameters of isolated mung bean hypocotyl mitochondria. Three compounds—tannic, gentisic, and p-coumaric acids—inhibited hypocotyl growth and when incubated with isolated hypocotyl mitochondria released respiratory control, inhibited respiration, and prevented substrate-supported Ca2+ and PO4 transport. Vanillic acid also inhibited hypocotyl growth and reduced mitochondrial Ca2+ uptake but did not affect respiration or respiratory control of isolated mitochondria. This is the first compound reported to selectively inhibit Ca2+ uptake in plant mitochondria. Two other phenolic compounds—α, 3,5-resorcylic and protocatechuic acids—showed no significant effect on hypocotyl growth and did not affect mitochondrial oxidative phosphorylation either separately or in various combinations. Four phenolic compounds—ferulic, caffeic, p-hydroxybenzoic, and syringic acids—showed a significant reduction in mung bean hypocotyl growth but did not inhibit any of the mitochondrial processes examined. The results show that phenolic compounds which alter respiration or coupling responses in isolated mitochondria also inhibit hypocotyl growth and may reflect a mechanism of action for these natural growth inhibitors. 相似文献
16.
Summary Application of gypsum (tagged Ca45SO4.2H2O) caused a considerable increase in dry matter yield and content of Ca, Ca45, Mg and K and Ca:Na and (Ca+Mg): (Na+K) ratios and a decrease in the content of Na, N and P in dhaincha tops. There was a
considerable increase in the total uptake of Ca, Mg, Na, K, N, P and Ca45 by plant tops in response to gypsum. Contribution of Ca from applied Ca45SO4 varied from 78.3 to 84.7 per cent of the total Ca in plant tops, whereas, its uptake from this source varied from 52.18 to
98.73 me per 100 g plant tops. re]19720705 相似文献
17.
Calcium influx in skeletal muscle at rest,during activity,and during potassium contracture 总被引:30,自引:17,他引:13
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Calcium influx in the sartorius muscle of the frog (Rana pipiens) has been estimated from the rate of entry of Ca45. In the unstimulated preparation it is about equal to what has been reported for squid giant axons, but that per impulse is at least 30 times greater than in nerve fibers. The enhanced twitch when NO-2 replaces Cl- in Ringer's is associated with at least a 60 per cent increase in influx during activity, whereas this anion substitution does not affect the passive influx significantly. Calcium entry during potassium contracture is even more markedly augmented than during electrical stimulation, but only at the beginning of the contracture; thus, when a brief Ca45 exposure precedes excess K+ application, C45 uptake is increased three- to fivefold over the controls not subjected to K+, whereas when C45 and K+ are added together, no measurable increase in Ca45 uptake occurs. These findings are in keeping with the brevity of potassium contracture in "fast (twitch)" fibers such as in sartorius muscle. 相似文献
18.
Abstract— Ethyleneglycol-bis (β-aminoethyl ether)-N-N'-tetraacetic acid (EGTA) inhibited the incorporation of 32Pi into phosphatidylinositol (PI) in rat diaphragm incubated in Ca2+-free Krebs-Ringer medium. Only the labelling of the PI was altered, and no effects on the pool size of PI or on the incorporation of 32Pi into other phospholipids were observed. The effect of EGTA was concentration-dependent and appeared to be related to its Caa+-chelating properties; the inhibition of the incorporation of 32Pi could be completely reversed by the addition of excess Ca2+ but not Mg2+. The inhibitory effect of the EGTA was progressively enhanced by lengthening the preincubation of the tissue with EGTA, an observation suggesting that chelation of intracellular or membrane-bound Ca2+, rather than extracellular Ca2+, was involved in the effect. In contrast to its inhibition of the incorporation of 32Pi EGTA enhanced the incorporation of [3H]inositol into PI, but this effect was accompanied by an appreciable increase in total uptake of [3Hlinositol by the tissue. Our results suggest that the level of intracellular Ca2+ plays a role in the regulation of the incorporation of 32Pi into PI. Addition of unlabelled α-glycerophosphate to the incubation medium of tissues which had been preincubated with 2-deoxy-d -glucose failed to cause a significant diminution in the inhibition by EGTA of the incorporation of 32Pi into PI. This experiment suggests, but does not prove, that the effect of EGTA was not at the level of incorporation of 32Pi into α-glycerophosphate. 相似文献
19.
SECOND MESSENGERS AND THE REGULATION OF CA 2+ FLUXES BY CA 2+ -MOBILIZING AGONISTS IN RAT LIVER 总被引:2,自引:0,他引:2
JOSEPH G. ALTIN FYFE L. BYGRAVE 《Biological reviews of the Cambridge Philosophical Society》1988,63(4):551-611
Knowledge of the mechanism of action of Ca2+-mobilizing agonists in liver has progressed considerably following the discovery that their interaction with specific receptors on the plasma membrane is accompanied by the hydrolysis of PIP2 and the generation of the second messengers diacylglycerol and IP3, for the activation of protein kinase C and the mobilization of intracellular Ca2+, respectively. Although the second messenger functions of diacylglycerol and IP3 in these actions seem well established, it is not yet clear how the agonists are able to regulate Ca2+ influx across the plasma membrane, an event which is crucial for those actions of the agonists which are dependent on the maintenance of an elevated level of cytosolic Ca2+, Whilst there is evidence for the existence of more than one pathway for Ca2+ influx in liver, it appears that in each instance the Ca2+ influx process is regulated differently to the Ca2+ influx through the volage-sensitive Ca2+ channels that is known to occur in excitable tissues. At present it is not clear whether any of the Ca2+ influx pathways in liver is regulated by direct coupling to the agonist receptor mechanism on the outer surface of the plasma membrane, or whether the regulation involves the production of some second messenger(s). However, indirect evidence from a number of tissues appears to favour the involvement of both IP3 and IP4 in the regulation of Ca2+ influx. The mechanism by which IP3 and IP4 may regulate Ca2+ influx remains to be established, but it has been proposed that Ca2+ entry into the cell occurs through a pathway connecting the plasma membrane and the endoplasmic reticulum, following the release of intracellular Ca2+ from the lumen of the endoplasmic reticulum. Although it is not yet known whether glucagon (or cyclic AMP) activates the same pathway for Ca2+ influx as Ca2+-mobilizing agonists, the marked potentiation by cyclic AMP of the Ca2+ influx induced by Ca2+-mobilizing agonists has provided a powerful system with which to study the regulation of Ca2+ influx in liver. Whether this Ca2+ influx process occurs through some ion exchange mechanism (such as Ca2+/Na+ exchange) remains to be determined. Results from this study suggests that the Ca2+ influx is inhibited by neomycin, acidic pH, and a depolarization of the plasma membrane. The observation that cyclic AMP synergistically potentiates the influx of Ca2+ induced by Ca2+-mobilizing agonists, that this influx appears to correlate with the reported ability of these agonists to induce PIP2 hydrolysis and accumulation of IP3, and that cyclic AMP synergistically potentiates the production of IP4 by vasopressin, are all consistent with the notion that IP3 and IP4 are involved in regulating Ca2+ influx. Whilst little is known about the Ca2+ transport process itself, these studies coupled with the recent finding that Ca2+ influx into the liver cell can occur through different pathways, seem set to lead to a better understanding of this important process in the near future. 相似文献
20.
《Bioorganic & medicinal chemistry letters》2014,24(15):3464-3468
The transient receptor potential ankyrin 1 (TRPA1) channel is activated by noxious stimuli including chemical irritants and endogenous inflammatory mediators. Antagonists of this channel are currently being investigated for use as therapeutic agents for treating pain, airway disorders, and itch. A novel azabenzofuran series was developed that demonstrated in vitro inhibition of allyl isothiocyanate (AITC)-induced 45Ca2+ uptake with nanomolar potencies against both human and rat TRPA1. From this series, compound 10 demonstrated in vivo target coverage in an AITC-induced flinching model in rats while providing unbound plasma concentrations up to 16-fold higher than the TRPA1 rat IC50. 相似文献