Structure of the oxidized long-chain flavodoxin from Anabaena 7120 at 2 A resolution

The structure of the long-chain flavodoxin from the photosynthetic cyanobacterium Anabaena 7120 has been determined at 2 A resolution by the molecular replacement method using the atomic coordinates of the long-chain flavodoxin from Anacystis nidulans. The structure of a third long-chain flavodoxin from Chondrus crispus has recently been reported. Crystals of oxidized A. 7120 flavodoxin belong to the monoclinic space group P2(1) with a = 48.0, b = 32.0, c = 51.6 A, and beta = 92 degrees, and one molecule in the asymmetric unit. The 2 A intensity data were collected with oscillation films at the CHESS synchrotron source and processed to yield 9,795 independent intensities with Rmerg of 0.07. Of these, 8,493 reflections had I > 2 sigma and were used in the analysis. The model obtained by molecular replacement was initially refined by simulated annealing using the XPLOR program. Repeated refitting into omit maps and several rounds of conjugate gradient refinement led to an R-value of 0.185 for a model containing atoms for protein residues 2-169, flavin mononucleotide (FMN), and 104 solvent molecules. The FMN shows many interactions with the protein with the isoalloxazine ring, ribityl sugar, and the 5'-phosphate. The flavin ring has its pyrimidine end buried into the protein, and the functional dimethyl benzene edge is accessible to solvent. The FMN interactions in all three long-chain structures are similar except for the O4' of the ribityl chain, which interacts with the hydroxyl group of Thr 88 side chain in A. 7120, while with a water molecule in the other two. The phosphate group interacts with the atoms of the 9-15 loop as well as with NE1 of Trp 57. The N5 atom of flavin interacts with the amide NH of Ile 59 in A. 7120, whereas in A. nidulans it interacts with the amide NH of Val 59 in a similar manner. In C. crispus flavodoxin, N5 forms a hydrogen bond with the side chain hydroxyl group of the equivalent Thr 58. The hydrogen bond distances to the backbone NH groups in the first two flavodoxins are 3.6 A and 3.5 A, respectively, whereas in the third flavodoxin the distance is 3.1 A, close to the normal value. Even though the hydrogen bond distances are long in the first two cases, still they might have significant energy because their microenvironment in the protein is not accessible to solvent.(ABSTRACT TRUNCATED AT 400 WORDS)

NMR study of the solution conformation of actinomycin D

The solution conformation of actinomycin D, the Gram-positive antibiotic and DNA-binding drug, has been determined by 1H-NMR in deuterated dimethyl sulfoxide. The structure determination is based on the experimental data set of NOE restraints. Four structures were obtained from the distance geometry and restrained molecular dynamics calculation. The resultant structures satisfy the experimental restraints very well. These structures are found to be compatible with the X-ray crystal structures.

IL-1 receptor antagonist protein production and gene expression in rheumatoid arthritis and osteoarthritis synovium

IL-1 can participate in the perpetuation of arthritis through direct stimulation of synoviocytes and augmentation of matrix degradation. Hence, local production of the IL-1R antagonist protein (IRAP) might be an important negative feedback signal that regulates synovitis. We assessed synovial IRAP production in synovia from 30 individuals, by using a specific mAb and the immunoperoxidase staining method. IRAP was detected in 11 of 12 rheumatoid arthritis (RA) synovial tissues (ST) and was located primarily in the sublining, particularly in perivascular regions enriched for macrophages. Some staining was observed in the intimal lining of the synovium, although this was significantly less than in the sublining (p less than 0.05). Nine of 12 osteoarthritis (OA) tissues were positive for IRAP. In contrast to RA, the staining was observed primarily in the synovial lining in OA, with only minimal sublining IRAP being detected. Synovia from four patients without arthritis were negative (three autopsy specimens and one post-traumatic sample). Of the other two patients with miscellaneous diagnoses, one sample was negative (tenosynovitis) and one was positive (seronegative inflammatory arthritis) (sublining). Studies of serial sections and double-immunostaining experiments indicated that macrophages are the major cells containing immunoreactive IRAP. IRAP gene expression in vivo was determined by performing in situ hybridization on ST from 17 arthritis patients. RNA sense IRAP probes did not hybridize to any tissues. Anti-sense IRAP probes bound to two of nine RA tissues, two of six OA tissues, one of one seronegative inflammatory arthropathy tissue, and none of one flexor tenosynovitis tissue. As with immunoreactive protein, IRAP mRNA was primarily localized to cells in the synovial lining in OA but was more prominent in perivascular lymphoid aggregates in RA and seronegative inflammatory arthropathy. Northern blot analysis was performed on RNA isolated from nine ST. The appropriately sized IRAP band was identified in six of nine samples (five of six RA and one of three OA). Supernatants from cultured RA and OA ST cells contained immunoreactive and biologically active IRAP. Hence, IRAP gene expression and protein production occur in RA and OA synovium, albeit in different distributions.

Multiple-model adaptive predictive control of mean arterial pressure and cardiac output

A multiple-model adaptive predictive controller has been designed to simultaneously regulate mean arterial pressure and cardiac output in congestive heart failure subjects by adjusting the infusion rates of nitroprusside and dopamine. The algorithm is based on the multiple-model adaptive controller and utilizes model predictive controllers to provide reliable control in each model subspace. A total of 36 linear small-signal models were needed to span the entire space of anticipated responses. To reduce computation time, only the six models with the highest probabilities were used in the control calculations. The controller was evaluated on laboratory animals that were either surgically or pharmacologically altered to exhibit symptoms of congestive heart failure. During trials, the controller performance was robust with respect to excessive switching between models and nonconvergence to a single dominant model. A comparison is also made with a previous multiple-drug controller design.

[Report on first finding an epidemic of Scrub typhus in north rural areas]

In the autumn of 1989 and 1990, an epidemic of Scrub typhus occurred in north rural areas in Tianjin. The authors investigated the epidemic on clinical, epidemiological, serological and etiological features, 44 patients were diagnosed serologically or clinically as Scrub typhus and 42 of them (95.5%) were diagnosed serologically by IFA method. 10 sera specimens collected from the patients were determined distinctively by CF method, 8 of them were > or = 1:20 titre to Gilliam type antigen of tsutsugamushi. The try for isolating pathogens failed of success. The epidemic areas is situated in 39.45'-40.05' north latitudes and showed it was the new epidemic area in the north of China.

[A research on the quality of radix Astragali]

Milkvetch root (Radix Astragali) and its likes were determined in their contents of trace elements, total extracts and astragalin A. The result showed there was some relationship between the drug quality, trace-element contents, difference of species, growing areas and on-the-spot processing methods.

IL-1 receptor antagonist protein production and gene expression in rheumatoid arthritis and osteoarthritis synovium

IL-1 can participate in the perpetuation of arthritis through direct stimulation of synoviocytes and augmentation of matrix degradation. Hence, local production of the IL-1R antagonist protein (IRAP) might be an important negative feedback signal that regulates synovitis. We assessed synovial IRAP production in synovia from 30 individuals, by using a specific mAb and the immunoperoxidase staining method. IRAP was detected in 11 of 12 rheumatoid arthritis (RA) synovial tissues (ST) and was located primarily in the sublining, particularly in perivascular regions enriched for macrophages. Some staining was observed in the intimal lining of the synovium, although this was significantly less than in the sublining (p less than 0.05). Nine of 12 osteoarthritis (OA) tissues were positive for IRAP. In contrast to RA, the staining was observed primarily in the synovial lining in OA, with only minimal sublining IRAP being detected. Synovia from four patients without arthritis were negative (three autopsy specimens and one post-traumatic sample). Of the other two patients with miscellaneous diagnoses, one sample was negative (tenosynovitis) and one was positive (seronegative inflammatory arthritis) (sublining). Studies of serial sections and double-immunostaining experiments indicated that macrophages are the major cells containing immunoreactive IRAP. IRAP gene expression in vivo was determined by performing in situ hybridization on ST from 17 arthritis patients. RNA sense IRAP probes did not hybridize to any tissues. Anti-sense IRAP probes bound to two of nine RA tissues, two of six OA tissues, one of one seronegative inflammatory arthropathy tissue, and none of one flexor tenosynovitis tissue. As with immunoreactive protein, IRAP mRNA was primarily localized to cells in the synovial lining in OA but was more prominent in perivascular lymphoid aggregates in RA and seronegative inflammatory arthropathy. Northern blot analysis was performed on RNA isolated from nine ST. The appropriately sized IRAP band was identified in six of nine samples (five of six RA and one of three OA). Supernatants from cultured RA and OA ST cells contained immunoreactive and biologically active IRAP. Hence, IRAP gene expression and protein production occur in RA and OA synovium, albeit in different distributions.

Metabolism in and function of the central dopamine system after transplanting adrenal medullary tissue into the rat brain

The unilateral nigrostriatal pathway of rats was destroyed by microinjecting 6-hydroxydopamine (6-OH-DA), and isogenous rat adrenal medullary tissue was then transplanted into the lesioned lateral caudate nucleus. After 2 months, rotational movement was almost abolished in 40% of the transplanted rats, and it was significantly reduced in the remaining 60%. Dopamine (DA) and its metabolites contents were significantly decreased in the lesioned side of the forebrain, while no changes of NA were found. After transplanting adrenal medullary tissue, the DA contents increased by 9% only, whereas the NA contents increased significantly. In addition, by examining synaptosomes in the brains of these rats, we found that on the lesioned side of nontransplanted rats, DA uptake and DA receptor binding were increased significantly, while no such changes were seen in the transplanted group.

Proliferating cell nuclear antigen in oesophageal diseases; correlation with transforming growth factor alpha expression

This study was designed to correlate mucosal proliferation in Barrett's oesophagus with expression of a growth promoting peptide, transforming growth factor alpha (TGF alpha). Oesophageal mucosa was studied from 50 patients with oesophageal disease who had been treated by oesophagectomy. Histological analysis showed a range of oesophageal pathology - 18 patients had gastric type Barrett's mucosa, 18 had intestinal type Barrett's mucosa, and 14 had oesophageal adenocarcinomas. Sections were stained immunohistochemically for proliferating cell nuclear antigen (PCNA) (an index of cellular proliferation) and TGF alpha. PCNA immunostaining was seen mainly in the basal cells of the neck/foveolar epithelial compartment of the glands in Barrett's oesophagus. However, in mucosa with high grade dysplasia, the proliferative compartment extended upwards into the superficial layers of the glands. At least 2000 cells were counted in each patient to determine the proportion with PCNA immunoreactivity (PCNA labelling index). The labelling index was highest in adenocarcinoma (25%) and in Barrett's intestinal type mucosa with high grade dysplasia (26%) compared with intestinal type mucosa with no significant dysplasia (20%) and Barrett's gastric type mucosa (12%). There was a significant positive correlation between PCNA labelling indices and TGF alpha expression in Barrett's mucosa (p less than 0.01). In glands showing high grade dysplasia, TGF alpha immunoreactivity was seen in the same regions of the glands as PCNA immunoreactivity, indicating the possibility of involvement of TGF alpha in (pre) neoplastic proliferation in Barrett's oesophagus.

RUBIDIUM, a program for computer-aided assignment of two-dimensional NMR spectra of polypeptides

Taking advantage of the rule-based expert system technology, a program named RUBIDIUM (Rule-Based Identification In 2D NMR Spectrum) was developed to accomplish the automatic 1H NMR resonance assignments of polypeptides. Besides noise elimination and peak selection capabilities, RUBIDIUM detects the cross-peak patterns of amino acid residues in the COSY spectrum, assigning these patterns to amino acid types, performing sequential assignments using combined COSY/NOESY spectra, and finally, achieving the total assignment of the 1H NMR spectrum.

Heterogeneous calcium currents and transmitter release in cultured mouse spinal cord and dorsal root ganglion neurons

1. Calcium currents and transmitter release were studied in cocultures of fetal mouse neurons from the ventral half of the spinal cord (VH neurons) and from dorsal root ganglion (DRG neurons). The effects of BayK 8644 and omega-conotoxin on calcium currents and transmitter release were compared. 2. The presence of low voltage-activated (LVA) calcium current in both VH and DRG neurons is variable. Some cells exhibit only high voltage-activated (HVA) currents, whereas others show both HVA and LVA currents. 3. BayK 8644 did not affect LVA currents but strongly augmented both steady and transient components of the HVA calcium conductance. 4. omega-Conotoxin GVIA reduces both transient and steady components of the HVA but does not abolish either component even after 3 h of application. 5. Calcium currents that were resistant to omega-contoxin were augmented by BayK 8644. 6. Synaptic transmission between pairs of spinal cord neurons from the ventral half of the spinal cord (VH-VH connections) or between dorsal root ganglion neurons and VH neurons (DRG-VH connections) were studied with two-cell recording and stimulation techniques. 7. In approximately 70% of VH-VH connections and 50% of DRG-VH connections, BayK 8644 or its active optical isomer failed to affect transmitter output. Substantial augmentation of the remainder of the connections could be reliably produced by the dihydropyridines. Raised calcium in the extracellular medium produced augmentation of synaptic connections in all cases. BayK 8644 produced substantial, consistent augmentation of voltage-sensitive calcium channels in both VH and DRG neurons. 8. The toxin, omega-conotoxin, produced no consistent effect on excitatory or inhibitory postsynaptic potentials (EPSPs or IPSPs) elicited in VH neurons by stimulation of nearby VH neurons. VH EPSPs elicited by stimulation of nearby DRG neurons were reduced to approximately 50% of control values after 10 min of omega-conotoxin perfusion. Spontaneous and evoked synaptic activity could be recorded in VH neurons as long as 2 h after cultures were incubated in 0.5 microM omega-conotoxin. omega-Conotoxin produced a modest reduction in HVA currents in both VH and DRG neurons. 9. BayK 8644 did not produce consistent augmentation of transmission at the frog neuromuscular junction. omega-Conotoxin produced total blockade of transmission in this preparation. 10. We conclude that neither sustained nor inactivating high-threshold voltage-sensitive (HVA) calcium channels sensitive to BayK 8644 or omega-conotoxin such as those measured in the neuronal cell bodies are responsible for action-potential-evoked transmitter release from the majority of VH neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Chitin utilization by marine bacteria. A physiological function for bacterial adhesion to immobilized carbohydrates

Chitin turnover is essential for recycling carbon and nitrogen in marine ecosystems. A key step in this process is the adhesion of marine bacteria to chitin-containing particulates. Vibrio species were therefore surveyed for their ability to bind to immobilized carbohydrates, and one, Vibrio furnissii, adhered to glycosides of three sugars, N-acetylglucosamine (the preferred ligand), D-mannose, and D-glucose. A single Ca(2+)-requiring lectin is responsible for binding to the three sugars. Cells adhering to the chitin analogue divided at the same rate as cells in liquid culture. The first progeny of adherent cells continued to bind to the beads, but the population gradually shifted to a large fraction of free swimming cells, a process that may be necessary for colonization. Metabolic energy is required for cell adhesion to the glycosides, and transient (or no) adhesion occurred in incomplete growth media. The results were explained by studying met and pro mutants. Both the initiation and maintenance of lectin-mediated adhesion requires continuous protein synthesis; expression of lectin activity is a major priority of these cells and functions under conditions adequate for minimal protein synthesis, but insufficient to support cell growth. The adhesion/deadhesion apparatus is apparently used to continuously monitor the nutrient status of the environment, i.e. as a nutrient sensorium. In incomplete medium, cells deadhere, presumably to migrate to a more favorable environment.

Chitin utilization by marine bacteria. Degradation and catabolism of chitin oligosaccharides by Vibrio furnissii

Chemotaxis of the marine bacterium Vibrio furnissii to chitin oligosaccharides has been described (Bassler, B. L., Gibbons, P. J., Yu, C., and Roseman, S. (1991) J. Biol. Chem. 266, 24268-24275). Some steps in catabolism of the oligosaccharides are reported here. GlcNAc, (GlcNAc)2, and (GlcNAc)3 are very rapidly consumed by intact cells, about 320 nmol of GlcNAc equivalents/min/mg of protein. (GlcNAc)4 is utilized somewhat more slowly. During these processes, there is virtually no release of hydrolysis products by the cells. The oligosaccharides enter the periplasmic space (via specific porins?) and are hydrolyzed by a unique membrane-bound endoenzyme (chitodextrinase) and an exoenzyme (N-acetyl-beta-glucosaminidase; beta-Glc-NAcidase). The genes encoding these enzymes have been cloned and expressed in Escherichia coli. The chitodextrinase cleaves soluble oligomers, but not chitin, to the di- and trisaccharides, while the periplasmic beta-GlcNAcidase hydrolyzes the GlcNAc termini from the oligomers. The end products in the periplasm, GlcNAc and (GlcNAc)2 (possibly (GlcNAc)3) are catabolized as follows. (a) Disaccharide pathway, A (GlcNAc)2 permease is apparently expressed by Vibrio furnissii. Translocated (GlcNAc)2 is rapidly hydrolyzed by a soluble, cytosolic beta-GlcNAcidase, and the GlcNAc is phosphorylated by an ATP-dependent, constitutive kinase to GlcNAc-6-P. (b) Monosaccharide pathway, Periplasmic GlcNAc is taken up by Enzyme IINag of the phosphoenolpyruvate:glycose phosphotransferase system, yielding GlcNAc-6-P, the common intermediate for both pathways. Finally, GlcNAc-6-P----Ac- + GlcNH2-6-P----Fru-6-P + NH3. (GlcNAc)2 is probably the "true" inducer of the chitin degradative enzymes described in this report and, depending on its concentration in the growth medium, differentially induces the periplasmic and cytosolic beta-GlcNAcidases. The disaccharide pathway appears to be the most important when the cells are confronted with low concentrations of the oligomers (e.g. in chemotaxis swarm plates). The relative activities of the induced enzymes suggest that the rate-limiting steps in oligosaccharide catabolism are the glycosidase activities in the periplasm.

Chitin utilization by marine bacteria. Chemotaxis to chitin oligosaccharides by Vibrio furnissii

The adhesion/deadhesion apparatus of the marine bacterium Vibrio furnissii (Yu, C., Lee, A., Bassler, B. L., and Roseman, S. (1991) J. Biol. Chem. 266, 24260-24267) probably catalyzes the first step in colonizing chitin. Evidence is presented here for a second step, chemotaxis to chitin hydrolysis products. V. furnissii swarms toward chitin oligomers (GlcNAc)n, n = 1-6, at initial concentrations as low as 10 microM. A modified capillary assay was used for quantitation; the cells exhibit low level constitutive taxis to GlcNAc but not to the oligosaccharides. A mutant defective in the GlcNAc receptor (IINag of the phosphotransferase system) showed inducible taxis to the oligosaccharides. Two (or more) independently inducible receptors with overlapping specificities recognize (GlcNAc)n, n = 2-4. (GlcNAc)5 and (GlcNAc)6 were inactive in the capillary assay; expression of this receptor(s) apparently require special induction conditions. The (GlcNAc)n, n = 1-4, chemoreceptors of V. furnissii may be the most potent reported for bacteria. L-Amino acids were weak, constitutive attractants; glutamine, not known to be an attractant in other bacteria, was the most effective amino acid. The most potent receptor in Escherichia coli, Tar (aspartate), is not expressed in V. furnissii. The chemotactic responses were greatly affected by growth and induction conditions and the presence of nutrients in the assay media. Taxis to GlcNAc and GlcNAc oligomers was optimally induced by growth in lactate medium containing 0.6 mM sugar, while growth on the sugar per se resulted in poor taxis. Chemotaxis to the sugars increased 2- to 3-fold when the cells were starved. Nutrients in the assay medium, especially compounds that feed into or are part of the Krebs cycle, were potent inhibitors of taxis to the sugars and Gln. With the exception of isocitrate, inhibition of taxis correlated with the rate of oxidation of these compounds. The results suggest a link between catabolism and taxis in this organism, i.e. interactions or "cross-talk" between systems that are regulated by protein phosphorylation (Stock, J. A., Ninfa, A. J., and Stock, A. M. (1989) Microbiol. Rev. 53, 450-490).

Camptothecin overcomes MDR1-mediated resistance in human KB carcinoma cells

In order to understand the high efficacy of camptothecin derivatives against human colon tumor xenografts in nude mice, we have studied the transport properties of camptothecin derivatives across cellular membranes of MDR1-overexpressing cells. MDR1 overexpression was shown to have little effect on camptothecin cytotoxicity; camptothecin was equally cytotoxic to both the drug-sensitive parental cell line, KB 3-1, and its multidrug-resistant derivative, KB V1. The ability of camptothecin to overcome MDR1-mediated resistance is most likely due to unimpaired accumulation of camptothecin in MDR1 cells as suggested from the following experiments: (a) cytotoxicity of camptothecin against KB V1 cells was not altered by the known MDR1-reversing agent, verapamil; (b) camptothecin was ineffective as compared with vinblastine in competing with [3H]azidopine for photoaffinity labeling of MDR1; (c) camptothecin was equally efficient in trapping cellular topoisomerase I molecules on chromosomal DNA in the form of cleavable complexes in both KB 3-1 and KB V1 cells. The mechanism by which camptothecin overcomes MDR1-mediated resistance has been further studied using a number of uncharged and charged camptothecin derivatives. In contrast to the uncharged camptothecin derivatives, such as 9-amino-camptothecin and 10,11-methylenedioxy-camptothecin, the charged camptothecin derivative, topotecan, showed reduced cytotoxicity against MDR1-overexpressing KB V1 cells. The reduced cytotoxicity of topotecan in KB V1 cells was due to the overexpression of MDR1 in KB V1 cells since verapamil restored both topotecan accumulation and cytotoxicity. These results suggest that the charge on camptothecin can affect the drug's sensitivity to MDR1. The possible effect of membrane permeability in determining drug selectivity of MDR1 is discussed.

The conformation of echinomycin in DMSO solution

The conformation of the antibiotic echinomycin in DMSO solution has been determined from two-dimensional NMR and distance geometry calculation with distance constraints. Five converged conformations were calculated with NOE distance constraints followed by restraint energy minimization.

Common cis-acting region responsible for transcriptional regulation of Bradyrhizobium japonicum hydrogenase by nickel, oxygen, and hydrogen

Bradyrhizobium japonicum expresses hydrogenase in microaerophilic free-living conditions in the presence of nickel. Plasmid-borne hup-lacZ transcriptional fusion constructs were used to study the regulation of the hydrogenase gene. The hydrogenase gene was transcriptionally induced under microaerobic conditions (0.1 to 3.0% partial pressure O2). The hydrogenase gene was not transcribed or was poorly transcribed in strictly anaerobic conditions or conditions above 3.0% O2. Hydrogen gas at levels as low as 0.1% partial pressure induced hydrogenase transcription, and a high level of transcription was maintained up to at least 10% H2 concentration. No transcription was observed in the absence of H2. Hydrogenase was regulated by H2, O2, and Ni when the 5'-upstream sequence was pared down to include base number -168. However, when the upstream sequence was pared down to base number -118, the regulatory response to O2, H2, and Ni levels was negated. Thus, a common cis-acting regulatory region localized within 50 bp is critical for the regulation of hydrogenase by hydrogen, oxygen, and nickel. As a control, the B. japonicum hemA gene which codes for delta-aminolevulinic acid synthase was also fused to the promoterless lacZ gene, and its regulation was tested in the presence of various concentrations of O2 and H2. hemA-lacZ transcription was not dependent on levels of Ni, O2, or H2. Two different hup-lacZ fusions were tested in a Hup- background, strain JH47; these hup-lacZ constructs in JH47 demonstrated dependency on nickel, O2, and H2, indicating that the hydrogenase protein itself is not a sensor for regulation by O2, H2, or nickel.

Calcium, network activity, and the role of NMDA channels in synaptic plasticity in vitro

Functionally effective neuronal circuits are constructed through a competitive process that requires patterned neuronal activity elicited by structured input from the environment. To explore the mechanisms of this activity-dependent synaptic restructuring, we have developed an in vitro preparation of mouse spinal cord neurons maintained in a 3-chambered cell-culture system. Sensory afferents that received chronic electrical stimulation for 3-5 d developed stronger synaptic connections than unstimulated afferents converging onto the same postsynaptic spinal cord neuron. Exposure to 100 microM DL-2-amino-5-phosphonovaleric acid (APV), an antagonist of the NMDA channel, during the stimulation period prevented the competitive advantage associated with electric stimulation. However, when APV was applied with a higher concentration of calcium (3 mM), activity-dependent synaptic plasticity was no longer inhibited by the NMDA receptor antagonist. This reversal of APV block of the plasticity was not impaired by reducing transmitter release with 3 mM magnesium (in addition to 3 mM calcium and APV). A suppressant effect of APV on spontaneous activity was observed, which was attributed to loss of the NMDA component of the EPSP. Activity-dependent plasticity was also blocked if spontaneous activity was suppressed with dilute tetrodotoxin (TTX; 5-10 nM), a dosage that reduces excitability of neurons but is insufficient to block sodium-dependent action potentials. These experiments bring into question how NMDA channel activation is involved in the processes of synaptic remodeling during development. The data suggest that postsynaptic activity is required for synaptic remodeling, but this activity need not involve NMDA receptor activation specifically for activity-evoked synaptic plasticity. Instead, the mechanism for plasticity appears to operate through calcium-dependent processes in general.

Two-dimensional NMR studies and secondary structure of cobrotoxin in aqueous solution

The 1H-NMR spectra of cobrotoxin, a neurotoxic protein isolated from Formosan cobra Naja naja atra, have been studied by two-dimensional NMR techniques. Of 62 amino acid residues in cobrotoxin, the complete assignments of 58 residues have been made. The resonances from several of the remaining residues have been identified but not yet specifically assigned. The secondary structure of an antiparallel triple- and double-stranded beta-sheet has also been determined by observing the NOE.

A circulatory model for combined nitroprusside-dopamine therapy in acute heart failure

A computer model was developed to approximate the hemodynamic responses of dopamine and nitroprusside in acute left ventricular pump failure. The model is intended to aid the design of a multiple drug infusion system. A non-linear electrical analog model with baroreflex feedback was used to simulate the circulatory system. Heart failure was represented by a reduction in left ventricular inotropy. Pharmacodynamic relationships between the drugs studied and several elements of the system were incorporated into the model to simulate the overall drug responses which include secondary interactions between vascular components. Despite several shortcomings, the model showed good agreement with experimental and clinical data.