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91.
Influence of Calcium on Dopamine Synthesis and Tyrosine Hydroxylase Activity in Rat Striatum 总被引:5,自引:5,他引:0
Abstract: We have investigated three aspects of the relationship between calcium and tyrosine hydroxylase activity in rat striatum. In the first series of experiments, we examined the hypothesis that the rise in dopamine synthesis during increased impulse flow results from a calcium-induced activation of tyrosine hydroxylase. Calcium (12.5–200 μ M ) had no effect when added to crude enzyme or enzyme partially purified by gel filtration. Moreover, incubation of synaptosomes with excess calcium (up to 3.5 m M ) had little or no effect on dopamine synthesis. Incubation with the depolarizing alkaloid veratridine (75 μ M ) did increase dopamine synthesis, but did not alter the activity of tyrosine hydroxylase subsequently prepared from the synaptosomes, despite the presumed rise in intracellular calcium. In the second series we examined the hypothesis that increased dopamine synthesis after axotomy results from activation of tyrosine hydroxylase owing to a decrease in intracellular calcium. Addition of the calcium chelator EGTA (100 μ M ) to crude or partially purified enzyme was without effect, whereas incubation of synaptosomes with EGTA (500 μM ) decreased cell-free enzyme activity. In the third experimental series we examined the relationship between calcium and activation of tyrosine hydroxylase by dibutyryl cyclic AMP. EGTA failed to alter the increase in the activity of tyrosine hydroxylase prepared from synaptosomes incubated with dibutyryl cyclic AMP. However, it blocked the increase in synaptosomal dopamine synthesis and dopamine content normally produced by the cyclic AMP analogue. Thus, tyrosine hydroxylase does not appear to be activated by either increases or decreases in calcium availability. However, calcium may be important for the maintenance of basal tyrosine hydroxylase activity, and may play an indirect role in the expression of tyrosine hydroxylase activation produced by other means. 相似文献
92.
A. Diez de los Rios N. E. DeRose W. McD Armstrong 《The Journal of membrane biology》1981,63(1-2):25-30
Summary Open-tip and liquid ion-exchanger microelectrodes were used to study the effects of cAMP (6mm, added to the serosal medium) on apical membrane potential (E
m
) and intracellular sodium, potassium, and chloride activities (a
Na
i
,a
K
i
,a
Cl
i
) inNecturus gallbladder under open-circuit conditions. Transepithelial potential difference (E
Tr
) was also measured. In the presence of cAMP,a
Cl
i
fell from about 1.5 times its equilibrium value to a level that corresponded to electrochemical equilibrium across the apical and basolateral cell membranes. Under these conditionsa
Na
i
decreased anda
K
i
increased,E
m
was unchanged andE
Tr
increased from virtually zero to a small but significant serosal positive value. The cAMP-induced increase ina
K
i
was abolished when Cl–-free incubation media were used. Addition of the Ca++-ionophore A23187 (0.5 g/ml) to the serosal medium had no effect onE
m
,E
Tr
, ora
Cl
i
. When A23187 was added to the mucosal medium,E
m
and the basolateral membrane potential hyperpolarized by about 20 mV and an increase in the outwardly directed electrochemical driving force for Cl– was observed. These results indicate that cAMP inhibits coupled transapical Na–Cl entry into epithelial cells ofNecturus gallbladder and suggest that this inhibition may not be mediated by an increase in intracellular Ca++ concentration. 相似文献
93.
Dermorphins, Opioid Peptides from Amphibian Skin, Act on Opioid Receptors of Mouse Neuroblastoma x Rat Glioma Hybrid Cells 总被引:1,自引:0,他引:1
Thomas Glaser Karin Hübner Roberto de Castiglione Bernd Hamprecht 《Journal of neurochemistry》1981,37(6):1613-1617
Dermorphin and its Hyp6 analogue are opiate-like heptapeptides originally discovered in frog skin and characterized by the presence of a D-Ala2 residue in their sequence. They were assayed for their capacity to compete with [3H]Leu-enkephalin for binding to opioid receptors in membranes of neuroblastoma x glioma hybrid cells. In the presence of 7 nM-[3H]Leu-enkephalin, the concentrations at which they caused 50% inhibition of [3H]enkephalin binding (IC50 values) are 0.1 micro M and 0.3 micro M, respectively. In contrast, the synthetic L-Ala2-dermorphin shows very low affinity for the opioid receptors. In addition, like other opioid peptides, dermorphin and hyp6-dermorphin inhibit the elevation by prostaglandin E1 (PGE1) of the level of adenosine 3':5'-cyclic monophosphate (cyclic AMP) (IC50 values 0.2 micro M and 0.4 micro M, respectively). The inhibition is prevented by the opiate antagonist naloxone, L-Ala2-dermorphin is at least three orders of magnitude less potent in inhibiting the PGE1-evoked increase in the level of cyclic AMP. The results show that peptides with an amino acid sequence quite different from that of the enkephalins can bind to opioid receptors of the hybrid cells. 相似文献
94.
95.
Regulation of Muscarinic Receptor-Mediated Cyclic GMP Synthesis by Cultured Mouse Neuroblastoma Cells 总被引:9,自引:7,他引:2
Mouse neuroblastoma clone N1E-115 has muscarinic acetylcholine receptors that mediate cyclic GMP synthesis. This receptor-mediated response is not significantly higher than background until the cells have been maintained in the stationary phase for at least 1 week. The basis of the influence of time in culture on the cyclic GMP response was investigated. The relative amount of cyclic GMP synthesized by intact cells was measured by radioactively labeling the GTP pool with [3H]guanine, incubating cells with agonists, and then chromatographically isolating [3H]cyclic GMP. Carbamylcholine-, ionophore X-537A-, and sodium azide-induced cyclic GMP formation increased with time in culture to a maximum of 13-, 9-, and 2.5-fold above basal, respectively. There was no change in the number or the apparent affinity of the muscarinic receptors as measured by [3H]quinuclidinyl benzylate ([3H]QNB) binding. In addition, there was no change in the apparent affinity of the receptors for agonist as measured by the ability of carbamylcholine to displace the specific binding of [3H]QNB. Guanylate cyclase activity per milligram protein and per cell in-creased six- and sevenfold, respectively, from day 0 to day 22. However, this increase in guanylate cyclase appeared to precede the marked increase in sensitivity of the cells to agonists. These data suggest that, in addition to guanylate cyclase and muscarinic receptors, there is another factor which is responsible for the development of this muscarinic receptor-mediated response. 相似文献
96.
Cytoskeletal proteins used as marker of differentiation in mouse terato;carcinoma cells 总被引:1,自引:0,他引:1
The cyclic AMP receptor protein (CRP) of Escherichia coli has been crystallized. The crystals are orthorhombic, space group , b = 97.1 Å, , with one dimeric CRP molecule per asymmetric unit. 相似文献
97.
The effects of DCMU and NaN3 were studied on menadione-mediated photophosphorylation in broken spinach chloroplasts kept in low oxygen tension in Tricine or HEPES buffers at either high or reduced irradiances. – (A) At high irradiance (131 W. m?2) and absence of NaN3 the ATP formation was inhibited by DCMU regardless of the type of buffer used. – (B) At high irradiance and presence of NaN3 some concentrations of DCMU stimulated, whilst others inhibited the ATP formation in a HEPES buffer. The ATP formation was predominantly inhibited by DCMU in a Tricine buffer. – (C) At reduced irradiance (57 W. m?2) the chloroplasts in a HEPES buffer were almost insensitive towards DCMU both in the presence and absence of NaN3. – (D) Chloroplasts in a Tricine buffer were slightly stimulated in their ATP formation by DCMU at reduced irradiance either with or without the presence of NaN3 in the experimental medium. When menadione acts as a terminal electron acceptor, oxygen is consumed on its reoxidation. The results indicate that this process may occur with oxygen released by the splitting of water as the main oxidant. – The data also demonstrate the importance of caution when selecting buffering substances as well as when choosing light intensities for experiments on photophosphorylation in chloroplasts. 相似文献
98.
B.A.M. Renckens S.E. Van Emst-De Bries J.J.H.H.M. De Pont S.L. Bonting 《Biochimica et Biophysica Acta (BBA)/General Subjects》1980,630(4):511-518
- 1. 1. The effect of stimulation of adenylate cyclase by pancreozymin-C-octapeptide on the cyclic AMP level of rat pancreatic fragments has been investigated.
- 2. 2. In normal Krebs-Ringer bicarbonate medium pancreozymin-C-octapeptide causes a slight increase in pancreatic cyclic AMP level; this increase can be considerably enhanced by incubation in a calcium-free incubation medium.
- 3. 3. The dose-responce curve for pancreazymin-C-octapeptide in calcium-free medium is shifted to lower peptide concentrations, compared to the curve in normal Krebs-Ringer bicarbonate medium.
- 4. 4. The maximal stimulatory effect of pancreozymin-C-octapeptide id obtained at a 1-methyl-3-isobutylxanthine concentration of 10 mM.
- 5. 5. It suffices to lower the Ca2+-concentration of the medium from 2.5 to 1.5 mM to get the maximal increase in cyclic AMP content under influence of pancreozymin-C-octapeptide.
- 6. 6. It is concluded that extracellular calcium antagonizes the stimulation of adenylate cyclase by pancreozymin-C-octapeptide. This suggest that a low cytoplasmic Ca2+-concentration is required for the maximal response of acinar cell adenylate cyclase to pancreozymin.
Keywords: cyclic AMP formation; Ca2+; Pancreozymin-C-octapeptide; Adeny; ate cyclase; (Rat pancreas) 相似文献
99.
Mechanism of activation of cyclic GMP-dependent protein kinase from rat liver by multiple modulators
Charles W. Mackenzie III Thomas E. Donnelly Jr. 《Biochimica et Biophysica Acta (BBA)/General Subjects》1980,633(3):444-456
A number of polyanionic compounds, including DNA, RNA and polyglutamate, were shown to exhibit protein kinase stimulatory modulator activity as they were required for cyclic GMP to stimulate the phosphorylation of various cationic substrates by rat liver cyclic GMP-dependent protien kinase. Anionic proteins (casein, phosvitin) were phosphorylated poorly by the enzyme and their phosphorylation was not stimulated by the stimulatory modulators. Studies of the mechanism of action suggest that the modulators interact directly with the substrates to form a complex which is a better substrate than free histone. The observed effect of modulator is complex as it depends on the ratio of modulator to histone and the resultant state of the complex formed (better or poorer substrate than free histone). The observed effect is also dependent on the properties of the histone substrate as Michaelis-Menten kinetics are not observed in the phosphorylation of arginine-rich histone in the absence or presence of cyclic GMP. 相似文献
100.