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121.
Increased intracellular calcium concentration ([Ca2+]i) is required for smooth muscle contraction. In tracheal and other tonic smooth muscles, contraction and elevated [Ca2+]i are maintained as long as an agonist is present. To evaluate the physiological role of steady-state increases in Ca2+ on tension maintenance, [Ca2+]i was elevated using ionomycin, a Ca2+ ionophore or charybdotoxin, a large-conductance calcium-activated potassium channel (KCa) blocker prior to or during exposure of tracheal smooth muscle strips to Ach (10–9 to 10–4
M). Ionomycin (5 µM) in resting muscles induced increases in [Ca2+]i to 500±230 nM and small increases in force of 2.6±2.3 N/cm2. This tension is only 10% of the maximal tension induced by ACh. Charybdotoxin had no effect on [Ca2+]i or tension in resting muscle. After pretreatment of muscle with ionomycin, the concentration-response relationship for ACh-induced changes in tension shifted to the left (EC50=0.07±0.05 µM ionomycin; 0.17±0.07 µM, control, p<0.05). When applied to the muscles during steady-state responses to submaximal concentrations of ACh, both ionomycin and charybdotoxin induced further increases in tension. The same magnitude increase in tension occurs after ionomycin and charybdotoxin treatment, even though the increase in [Ca2+]i induced by charybdotoxin is much smaller than that induced by ionomycin. We conclude that the resting muscle is much less sensitive to elevation of [Ca2+]i when compared to muscles stimulated with ACh. Steady-state [Ca2+]i limits tension development induced by submaximal concentrations of ACh. The activity of KCa moderates the response of the muscle to ACh at concentrations less than 1 µM. 相似文献
122.
José de JesÚs Garcia M. Tuena de Gómez-Puyou A. Gómez-Puyou 《Journal of bioenergetics and biomembranes》1995,27(1):127-136
The effect of trifluoperazine (TFP) on the ATPase activity of soluble and paniculate F1ATPase and on ATP synthesis driven by succinate oxidation in submitochondrial particles from bovine heart was studied at pH 7.4 and 8.8. At the two pH. TFP inhibited ATP hydrolysis. Inorganic phosphate protected against the inhibiting action of TFP. The results on the effect of various concentrations of phosphate in the reversal of the action of TFP on hydrolysis at pH 7.4 and 8.8 showed that H2PO
4
–
is the species that competes with TFP. The effect of TFP on oxidative phosphorylation was studied at concentrations that do not produce uncoupling or affect the aerobic oxidation of succinate (<15M). TFP inhibited oxidative phosphorylation to a higher extent at pH 8.8 than at pH 7.4; this was through a diminution in theV
max, and an increase in theK
m for phosphate. Data on phosphate uptake during oxidative phosphorylation at several pH showed that H2PO
4
–
is the true substrate for oxidative phosphorylation. Thus, in both synthesis and hydrolysis of ATP, TFP and H2PO
4
–
interact with a common site. However, there is a difference in the sensitivity to TFP of ATP synthesis and hydrolysis; this is more noticeable at pH 8.8, i.e. ATPase activity of soluble F1 remains at about 40% of the activity of the control in a concentration range of TFP of 40–100M, whereas in oxidative phosphorylation 14M TFP produces a 60% inhibition of phosphate uptake. 相似文献
123.
Dinitrogen-fixing legumes are frequently assumed to be less water-use efficient than plants utilizing soil mineral N, because of the high respiratory requirements for driving N2 fixation. However, since respiration is assumed not to discriminate against 13C, any differences in water-use efficiency exclusively due to respiration should not be apparent in carbon isotope discrimination () values. Our objective was to determine if the source of N (N2 fixation versus soil N) had any effect on of field-grown grain legumes grown at different elevations. Four legume species, Glycine max, Phaseolus lunatus, P. vulgaris, and Vigna unguiculata, were grown on five field sites spanning a 633 m elevational gradient on the island of Maui, Hawaii. The legumes were either inoculated with a mixture of three effective strains of rhizobia or fertilized weekly with urea at 100 kg N ha-1 in an attempt to completely suppress symbiotic N2-fixing activity. In 14 of 20 analyses of stover and 12 of 15 analyses of seed values were significantly higher (p=0.10) in the inoculated plants than the N-fertilized plants. Nitrogen concentrations were generally higher in the fertilized treatments than the inoculated treatments. The different values obtained depending on N-source may have implications in using as an indicator of water-use efficiency or yield potential of legumes. 相似文献
124.
Rhizodeposition under ambient and elevated CO2 levels 总被引:1,自引:0,他引:1
Peter R. Darrah 《Plant and Soil》1995,187(2):265-275
As global CO2 levels rise, can soils store more carbon and so buffer atmospheric CO2 levels? Answering this question requires a knowledge of the rates of C inputs to soil and of CO2 outputs via decomposition. Below-ground inputs from roots are a major component of the C flow into soils but are still poorly understood. In this article, new techniques for measuring rhizodeposition are reviewed and discussed and the need for cross-comparisons between methods is identified. One component of rhizodeposition, root exudation, is examined in more detail and evidence is presented which suggests that current estimates of exudate flow into soils are incorrect. A mechanistic mathematical model is used to explore how exudate flows might change under elevated CO2. 相似文献
125.
Previous studies showed that localization of nucleophosmin/B23 (NPM) to nucleoli requires adequate cellular GTP levels (Finchet al., J Biol Chem 268, 5823–5827, 1993). In order to study whether hydrolysis of GTP plays a role in NPM localization, we introduced a nonhydrolyzable GTP analog into HeLa cells. Cells were first depleted of GTP with the IMP dehydrogenase inhibitor, mycophenolic acid (MA), to induce translocation of NPM from the nucleoli to the nucleoplasm. Non-hydrolyzable GTP analogs were then introduced into cells by electroporation. We found that introduction of the non-hydrolyzable analog, GTPS, was effective in restoring NPM localization to nucleoli. Cells incubated in medium containing G-nucleotides without electroporation showed no effect. To reduce the possibility that cells use guanine from degraded nucleotide to supplement GTP pools via salvage pathways, experiments were also performed in the presence of (6-mercaptopurine) 6MP, a competitive inhibitor of the salvage enzyme, HGPRT (hypoxanthine guanine phosphoribosyl transferase), in addition to MA. Under these conditions, introduction of GTPS still effectively restored the localization of NPM into nucleoli. This study demonstrates that electroporation can be used effectively to introduce nucleotides into cultured cells without excessive loss of viability. Our results also indicate that the GTP dependent localization of NPM to the nucleoli may not require GTP hydrolysis. 相似文献
126.
Summary Versatile three-step procedures for syntheses of seven racemi-fluoro-a-amino acids are described. Alkylation oftert-butyl N-(diphenylmethylene) glycinate with 1-bromo-2-fluoroalkanes gave N-protected aminoacid esters both in anhydrous medium using lithium-diisopropylamide as base at low temperature or in a two phase system of 50% aqueous sodium hydroxide and methylene chloride with triethylbenzylammonium chloride as the phase transfer catalyst at room temperature. Subsequent two-step deprotection with citric acid and hydrochloric acid gave the title compounds in 13–33% overall yields.Dedicated to Professor Dr.mult., Dr.h.c. Alois Haas on the occasion of his 65th birthday 相似文献
127.
David Cowburn 《Current opinion in structural biology》1997,7(6):835-838
Protein tyrosine binding (PTB) and ‘post synaptic density disc-large zo-1’ (PDZ) domains bind to short peptidic ligands by augmentation of one of the domain's β sheets and other recognition mechanisms. The two domain classes have a superficial resemblance to each other, even though no sequential homology exists. The structural bases of the interactions are well understood for the domains now experimentally determined, and ligand—target pairs can probably be identified in favorable cases by analogy with the known domains. For both PTB and PDZ classes, functional activities are still not fully defined: it is possible that these domain classes, along with pleckstrin homology domains, have multiple roles. 相似文献
128.
Conclusion Membrane association is essential for GRK function and because of this the GRKs have evolved complex regulatory mechanisms
for associating with the membrane. Although the GRKs are highly homologous, each kinase utilizes a distinct mechanism for
associating with the membrane, which makes it unique within the family. Initially, the carboxyl terminus of the GRKs was identified
as the “membrane association domain” but recent evidence suggests that the amino terminus may also play a critical role in
localizing the kinases to the membrane (Murga et al., 1996; Pitcher et al, 1996). It is within these two domains that the
GRKs are most variable at the amino acid level. The GRKS exhibit an absolute requirement for phospholipids not only for association
with the membrane but also for activity. There are differences in preference and binding sites for the phospholipids within
the GRK family, which may reflect differential targeting of the GRKs to G protein-coupled receptors situated in different
lipid environments. There are hundreds of G protein-coupled receptors and only six known GRKs. All the GRKs appear to phosphorylate
the same receptor substrates in vitro (Sterne-Marr & Benovic, 1995; Premont et al., 1995). Receptor specificity, in a cellular 相似文献
129.
BCL-2-Related Protein Expression in Apoptosis: Oxidative Stress Versus Serum Deprivation in PC12 Cells 总被引:5,自引:0,他引:5
Abstract: Expression of the BCL-2 protein family members, BAX, BAK, BAD, BCL-xL, BCL-xS, and BCL-2, was measured (by western blotting using specific antibodies) in PC12 cells before and during apoptosis induced by either H2 O2 treatment or by serum deprivation and during rescue from apoptosis by nerve growth factor (NGF). H2 O2 -induced apoptosis, as measured by DNA fragmentation, caused: (a) a dose-dependent increase in BAX, (b) a dose-independent increase in BAK, and (c) a dose-dependent inhibition of BAD expression. By comparison, apoptosis induced by serum deprivation resulted in a time-dependent decrease in both BAX and BAK, along with a dramatic and sudden decrease in BAD expression. However, when PC12 cells were incubated in an apoptosis-sparing medium (i.e., NGF-supplemented serum-free medium), both BAX and BAK were increased significantly, whereas BAD expression remained inhibited. BCL-xL expression was increased by H2 O2 but unaffected by serum deprivation or long-term NGF treatment. Neither BCL-2 nor BCL-xS expression could be detected in PC12 cells under the experimental conditions tested. Our results show that the expression of BAX, BAK, BAD, and BCL-xL is altered in a stimulus-dependent manner but cannot be used to define whether a cell will undergo or survive apoptosis. The similarity between changes in expression of BCL-2-related proteins induced by H2 O2 exposure and NGF rescue could reflect activation in part of a common antioxidant pathway. 相似文献
130.
Hanna M. Pappius 《Neurochemical research》1995,20(11):1311-1321
Changes with time after injury in behavioral deficits, as determined by the Morris swim test, and the in vivo specific binding of HEAT, a selective 1-adrenoreceptor ligand, were compared with the time-course of development of cortical hypometabolism in rats with focal freezing lesions. In our trauma model, cortical hypometabolism was detectable in the lesioned hemisphere at 4 hr, became maximal (50% of normal) at 3 days and diminished towards normal on days 5 and 10 post-injury. Progressive impairment of acquisition of the Morris water maze task was demonstrated up to day 3 post-lesion with improvement thereafter. On day 3 the latency to reach criterion was 60% longer in lesioned animals than in corresponding sham-operated ones. An increase in the volume of distribution of HEAT, limited to cortical areas of the lesioned hemisphere, was demonstrable at 4 hr post-lesion and reached its maximum on day 3 (200% of normal) with subsequent return toward normal on days 5 and 10. Several types of drugs were shown previously to modify the cortical hypometabolism associated with cerebral injury. The present data indicate that the same drugs also modify the in vivo binding of HEAT and the behavioral deficits induced by brain lesions. Ibuprofen, a non-steroidal anti-inflammatory drug, p-chlorophenylalanine, an inhibitor of serotonin synthesis, ketanserin, a specific 5HT2-receptor antagonist, and prazosin, an 1-adrenergic receptor blocker all normalized the in vivo binding of HEAT in the cortical areas of the lesioned hemisphere. All groups of animals treated with these drugs also showed subtle, but statistically highly significant improvements in latency to locate the platform in the Morris water maze. Taken together these results show good correlation between behavioral deficits, changes in 1-noradrenergic receptor binding and cortical hypometabolism in injured brain. This supports the hypothesis that post-injury cortical hypometabolism is a reflection of cortical functional depression in which both the serotonergic and noradrenergic neurotransmitter systems play a role, compatible with their inhibitory effects in the cortex and their postulated involvement in cortical information processing.Special issue dedicated to Dr. Leon S. Wolfe. 相似文献