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2.
Magdalena Torres M. France Bader Dominique Aunis M. Teresa Miras-Portugal 《Journal of neurochemistry》1987,48(1):233-235
Chromaffin cells both recently isolated or in culture present a high-affinity adenosine transporter with a Km value of 1 microM. When cells were exposed to nerve growth factor (NGF; 10 ng/ml), the adenosine transporter affinity decreased to 3 microM. This value was maintained from 3 days after plating to the end of the culture period. A change in the transport capacity was observed, with a significant increase (approximately 200-260%) in NGF-cultured cells throughout the period studied. 相似文献
3.
Bader FG 《Biotechnology and bioengineering》1987,30(1):37-51
A methodology for mathematically analyzing agitator performance and mass transfer in large multiturbine production fermentors is presented. The application of this approach provides a method for determining axial dissolved oxygen profiles under conditions of known mass transfer rates as a function of agitation-aeration characteristics. A stagewise approach is used which divides the fermentor into a series of mixing cells. This allows for each turbine and mixing cell to be individually optimized. The model also permits the determination of the mass transfer coefficient for each turbine based upon limited dissolved oxygen data. The primary limitation of this approach rests in the limited data and correlations available for multiturbine systems. The structure of the modelling approach can serve as a basis for testing single turbine correlations and adapting them to multiturbine systems. The step-by-step details of the mathematical analysis are presented and interpreted. A series of computer simulations demonstrate the effect of typical fermentor operating variables on the axial dissolved oxygen profile. Further simulations demonstrate the effect of modifying agitator blade numbers on the dissolved oxygen profile and agitator power requirement. 相似文献
4.
Effect of secretagogues on chromogranin A synthesis in bovine cultured chromaffin cells. Possible regulation by protein kinase C. 总被引:4,自引:1,他引:3 下载免费PDF全文
Chromogranin A is a major component of storage granules in many different secretory cell types. After [35S]methionine labelling of proteins from cultured bovine chromaffin cells, chromogranin A was immunoprecipitated with specific antibodies, and the radioactivity incorporated into chromogranin A was determined and used as an index of its synthesis rate. Depolarization of cells with nicotine or high K+ evoked a Ca2+-dependent increase in chromogranin A synthesis, whereas muscarine, which does not evoke significant Ca2+ influx from bovine chromaffin cells, had no effect on chromogranin A synthesis. Forskolin, an activator of adenylate cyclase, affected neither the basal nor the nicotine-stimulated rate of chromogranin A synthesis. In contrast, 12-O-tetradecanoylphorbol 13-acetate (TPA), an activator of protein kinase C, significantly enhanced the incorporation of radioactivity into chromogranin A. Sphingosine, an inhibitor of protein kinase C, abolished both nicotine-stimulated and TPA-induced chromogranin A synthesis. In addition, long-term treatment of chromaffin cells with TPA decreased protein kinase C activity and inhibited the nicotine-stimulated chromogranin A synthesis. These results suggest that protein kinase C may play an important role in the control of chromogranin A synthesis. 相似文献
5.
Transient expression of a Ca2+-activated Cl- current during development of quail sensory neurons 总被引:1,自引:0,他引:1
The expression of a calcium-activated chloride current (ICl(Ca)) was studied during the development of the sensory neurons of quail trigeminal ganglia. This current is expressed in 20% of the neurons by the 5th day of embryonic development; it can be found in nearly all neurons by the 7th day and subsequently disappears in half of them. Similar results were obtained with dorsal root ganglion neurons. The disappearance of ICl(Ca) in part of the sensory neurons during development is not due to a selective death of the neurons possessing this current and our results suggest that it is mediated by an interaction of the sensory neurons with their target tissue. 相似文献
6.
Peripheral actin filaments control calcium-mediated catecholamine release from streptolysin-O-permeabilized chromaffin cells 总被引:16,自引:0,他引:16
Adrenal medullary chromaffin cells were permeabilized by treatment with a streptococcal cytotoxin streptolysin O (SLO) which generates pores of macromolecular dimensions in the plasma membrane. SLO did not provoke spontaneous release of catecholamines or chromogranin A, a protein marker of the secretory granule, showing the integrity of the secretory vesicle membrane. However, the addition of micromolar free calcium concentration induced the corelease of noradrenaline and chromogranin A, indicating that secretory products are liberated by exocytosis. Calcium-dependent exocytosis from SLO-permeabilized cells required Mg-ATP and could not occur in the presence of other nucleotides. The pores generated by the toxin were large enough to introduce proteins, e.g., immunoglobulins, but also caused efflux of the cytosolic marker lactate dehydrogenase. Despite this, the cells remained responsive to calcium for up to 30 min after permeabilization, indicating that they retained their secretory machinery. In the search for a functional role of cytoskeletal proteins in the secretory process, we used SLO-permeabilized cells to examine the localization of filamentous actin, using rhodamine-phalloidin, and that of the actin-severing protein, gelsolin, using specific antibodies. It was found that both F-actin and gelsolin were exclusively localized in the subplasmalemmal region of the cell. We examined the relationship between actin disassembly, the elevation of intracellular calcium and secretion in SLO-treated cells. F-Actin destabilizing agents such as cytochalasin D or DNase I were found to potentiate calcium-stimulated release. The maximal effect was observed at low calcium concentrations (1-4 microM) and at the later stages of the secretory response (after 10 min stimulation). In addition, using rhodamine-phalloidin, we observed that calcium provoked simultaneously both cortical actin disassembly and catecholamine release in SLO-permeabilized cells. These results demonstrate that a close relationship exists between the secretory response and actin disassembly and provide further evidence that intracellular calcium controls the subplasmalemmal cytoskeletal actin organization and thereby the access of secretory granules to exocytotic sites. 相似文献
7.
Electrophysiology of a chick neuronal nicotinic acetylcholine receptor expressed in Xenopus oocytes after cDNA injection 总被引:12,自引:0,他引:12
Brain nicotinic acetylcholine receptors (nAChRs) are made up of protein subunits that differ from those constituting muscle nAChRs. To characterize the physiological properties of one class of avian brain nicotinic receptor, we injected the nuclei of Xenopus oocytes with full-length cDNAs for the ligand binding (alpha 4) and structural (n alpha) subunits. Injected oocytes had large ACh-induced currents in the microampere range that were insensitive to alpha-bungarotoxin, as expected for neuronal nAChRs. We found that these brain nAChRs incorporate at least two alpha 4 subunits and that their functional properties differ from muscle nAChRs in at least two respects: the elementary conductance is considerably smaller (20 pS), and channels in outside out patches stop functioning within a few minutes. 相似文献
8.
Site-directed mutagenesis of beta-galactosidase (E. coli) reveals that tyr-503 is essential for activity 总被引:1,自引:0,他引:1
M Ring D E Bader R E Huber 《Biochemical and biophysical research communications》1988,152(3):1050-1055
By using the technique of site-directed mutagenesis we have succeeded in replacing tyr-503 of beta-galactosidase (E. coli) with a phe. A study of the kinetic and stability properties of this mutant enzyme (F-503 beta-galactosidase) showed that the loss in activity upon this change is due to the loss of a catalytic group (rather than a detrimental change in the enzyme's overall structure or a change in the enzyme's binding capacity). This confirms previous suggestions that this tyr residue is involved in catalysis. 相似文献
9.
Gianfranco Menestrina Klaus-Peter Voges Günther Jung Günther Boheim 《The Journal of membrane biology》1986,93(2):111-132
Summary The voltage-dependence of channel formation by alamethicin and its natural analogues can be described by a dipole flip-flop gating model, based on electric field-induced transbilayer orientational movements of single molecules. These field-induced changes in orientation result from the large permanent dipole moment of alamethicin, which adopts -helical conformation in hydrophobic medium. It was, therefore, supposed that the only structural requirement for voltage-dependent formation of alamethicin-type channels might be a rigid lipophilic helical segment of minimum length.In order to test this hypothesis we synthesized a family of lipophilic polypeptides—Boc-(Ala-Aib-Ala-Aib-Ala)
n
-OMe,n=1–4—which adopt -helical conformation forn=2–4 and studied their interaction with planar lipid bilayers. Surprisingly, despite their large difference in chain length, all four polypeptides showed qualitatively similar behavior. At low field strength of the membrane electric field these polypeptides induce a significant, almost voltage-independent increase of the bilayer conductivity. At high field strength, however, a strongly voltage-dependent conductance increase occurs similar to that observed with alamethicin. It results from the opening of a multitude of ion translocating channels within the membrane phase.The steady-state voltage-dependent conductance depends on the 8th–9th power of polypeptide concentration and involves the transfer of 4–5 formal elementary charges. From the power dependences on polypeptide concentration and applied voltage of the time constants in voltage-jump current-relaxation experiments, it is concluded that channels could be formed from preexisting dodecamer aggregates by the simultaneous reorientation of six formal elementary charges. Channels exhibit large conductance values of several nS, which become larger towards shorter polypeptide chain length. A mean channel diameter of 19 Å is estimated corresponding roughly to the lumen diameter of a barrel comprised of 10 -helical staves. Similar to experiments with the N-terminal Boc-derivative of alamethicin we did not observe the burst sequence of nonintegral conductance steps typical of natural (N-terminal Ac-Aib)-alamethicin. Saturation in current/voltage curves as well as current inactivation in voltage-jump current-relaxation experiments are found. This may be understood by assuming that channels are generated as dodecamers but, while reaching the steady state, reduce their size to that of an octamer or nonamer. We conclude that the overall behavior of these synthetic polypeptides is very similar to that of alamethicin. They exhibit the same concentration and voltage-dependences but lack the stabilizing principle of resolved channel states characteristic of alamethicin. 相似文献
10.