Alteration of Ca2+ dependence of neurotransmitter release by disruption of Ca2+ channel/syntaxin interaction

Presynaptic N-type calcium channels interact with syntaxin and synaptosome-associated protein of 25 kDa (SNAP-25) through a binding site in the intracellular loop connecting domains II and III of the alpha1 subunit. This binding region was loaded into embryonic spinal neurons of Xenopus by early blastomere injection. After culturing, synaptic transmission of peptide-loaded and control cells was compared by measuring postsynaptic responses under different external Ca2+ concentrations. The relative transmitter release of injected neurons was reduced by approximately 25% at physiological Ca2+ concentration, whereas injection of the corresponding region of the L-type Ca2+ channel had virtually no effect. When applied to a theoretical model, these results imply that 70% of the formerly linked vesicles have been uncoupled after action of the peptide. Our data suggest that severing the physical interaction between presynaptic calcium channels and synaptic proteins will not prevent synaptic transmission at this synapse but will make it less efficient by shifting its Ca2+ dependence to higher values.     

Folding dynamics and mechanism of beta-hairpin formation

Protein chains coil into alpha-helices and beta-sheet structures. Knowing the timescales and mechanism of formation of these basic structural elements is essential for understanding how proteins fold. For the past 40 years, alpha-helix formation has been extensively investigated in synthetic and natural peptides, including by nanosecond kinetic studies. In contrast, the mechanism of formation of beta structures has not been studied experimentally. The minimal beta-structure element is the beta-hairpin, which is also the basic component of antiparallel beta-sheets. Here we use a nanosecond laser temperature-jump apparatus to study the kinetics of folding a beta-hairpin consisting of 16 amino-acid residues. Folding of the hairpin occurs in 6 micros at room temperature, which is about 30 times slower than the rate of alpha-helix formation. We have developed a simple statistical mechanical model that provides a structural explanation for this result. Our analysis also shows that folding of a beta-hairpin captures much of the basic physics of protein folding, including stabilization by hydrogen bonding and hydrophobic interactions, two-state behaviour, and a funnel-like, partially rugged energy landscape.     

Overexpression of the Bcl-2 protein increases the half-life of p21Bax

Bcl-2 and Bax are homologous proteins which can heterodimerize with each other. These proteins have opposing effects on cell survival when overexpressed in cells, with Bcl-2 blocking and Bax promoting apoptosis. Here we demonstrate that gene transfer-mediated elevations in Bcl-2 protein levels result in a marked increase in the steady-state levels of endogenous p21Bax protein as determined by immunoblotting in the Jurkat T-cell and 697 pre-B-cell leukemia cell lines, but not in several other cell lines including CEM T-cell leukemia, 32D.3 myeloid progenitor, PC12 pheochromocytoma, and NIH-3T3 fibroblasts. Steady-state levels of p21Bax protein were also elevated in the lymph nodes of Bcl-2 transgenic mice in which a BCL-2 transgene is expressed at high levels in B-cells. Northern blot analysis of BCL-2-transfected and control-transfected Jurkat and 697 leukemia cells revealed no Bcl-2-induced alterations in the steady-state levels of BAX mRNAs. In contrast, L-[35S]methionine pulse-chase analysis indicated a marked increase in the half-life (t1/2) of the p21Bax protein in BCL-2-transfected 697 cells compared to control-transfected cells (t1/2 > 24 h versus approximately 4 h), whereas the rate of Bax degradation was unaltered in Bcl-2-transfected CEM cells. The results demonstrate that levels of the proapoptotic p21Bax protein can be post-translationally regulated by Bcl-2, probably in a tissue-specific fashion, and suggest the existence of a feedback mechanism that may help to maintain the ratio of Bcl-2 to Bax protein in physiologically appropriate ranges.     

Transbrachial endovascular exclusion of an axillary artery pseudoaneurysm with PTFE-covered stents

PURPOSE: Endovascular exclusion of arterial injuries associated with arteriovenous fistulas and pseudoaneurysms has only recently been described using various stent-graft prostheses. This report details a transbrachial technique used to exclude an axillary artery pseudoaneurysm developing at the axillary anastomosis of an axillofemoral graft. METHODS AND RESULTS: Thin-walled polytetrafluoroethylene was expanded with an angioplasty balloon catheter and used to cover standard Palmaz stents. Two covered stents were delivered under fluoroscopic guidance via open brachial artery access to the site, resulting in complete exclusion of the pseudoaneurysm. Follow-up duplex scanning confirmed aneurysm exclusion 3 months postprocedure. CONCLUSIONS: This technique can be applied in arteries of different sizes and lengths, using currently available materials. However, the long-term behavior of these devices in the arterial tree must be determined before their widespread use can be recommended for most indications.     

An analysis of automatic teller machine usage by older adults: a structured interview approach

Sex differences in the activity of aromatase cytochrome P450 (CYP19) in the rat brain have been reported during pre- and postnatal development. It is unclear, however, whether these differences are reflected by corresponding differences in specific mRNA levels. To address this question, we have examined aromatase mRNA levels in specific regions of male and female rat brains by means of in situ hybridization (ISH). At prenatal stages of development, i.e. at gestational day 18 (GD18) and GD20, aromatase mRNA was detected in several preoptic, hypothalamic and limbic brain regions. Semiquantitative analysis of aromatase mRNA did not reveal sex differences in any of these regions. In contrast, clear-cut sex differences were determined at postnatal day (PN) 2; male animals expressed significantly more aromatase mRNA in the bed nucleus of stria terminalis (BST) and the sexually dimorphic nucleus of the preoptic area (SDN). Smaller but still significant differences (females > males) were obtained in the medial preoptic area (MPO). At PN6, sex differences of aromatase mRNA signals (males > females) were still present in the BST, but were no longer detectable in the SDN and the MPO. At PN15 and in adult animals, aromatase mRNA levels were similar in BST and medical amygdaloid nucleus of male and female rats. Since aromatase mRNA expression decreases during postnatal development, no ISH signals could be detected anymore in MPO, SDN and ventromedial hypothalamic nucleus. Our results are consistent with the concept that differential regulation of aromatase mRNA expression might be important for the establishment of different neuronal circuitry in male and female animals.     

Daily repetitive transcranial magnetic stimulation (rTMS) improves mood in depression

Converging evidence points to hypofunction of the left prefrontal cortex in depression. Repetitive transcranial magnetic stimulation (rTMS) activates neurons near the surface of the brain. We questioned whether daily left prefrontal rTMS might improve mood in depressed subjects and report a pilot study of such treatment in six highly medication-resistant depressed inpatients. Depression scores significantly improved for the group as a whole (Hamilton Depression Scores decreased from 23.8 +/- 4.2 (s.d.) at baseline to 17.5 +/- 8.4 after treatment; t = 3.03, 5DF, p = 0.02, two-tailed paired t-test). Two subjects showed robust mood improvement which occurred progressively over the course of several weeks. In one subject, depression symptoms completely remitted for the first time in 3 years. Daily left prefrontal rTMS appears to be safe, well tolerated and may alleviate depression.     

Somatic mutations in the thyrotropin receptor gene and not in the Gs alpha protein gene in 31 toxic thyroid nodules

Studies on frequency and distribution pattern of TSH receptor (TSHR) and Gs alpha protein (gsp) mutations in toxic thyroid nodules (TTNs) reported conflicting results, most likely also related to the different screening methods applied and the investigation of only part of exon 10 of the TSHR. Therefore, we screened a consecutive series of 31 TTNs for both TSHR and gsp mutations by direct sequencing of exon 9 and the entire exon 10 of the TSHR gene and exons 7-10 of the gsp gene. Somatic TSHR mutations were identified in 15 of 31 TTNs. TSHR mutations were localized in the third intracellular loop (Asp619Gly and Ala623Val), the sixth transmembrane segment (Phe631Leu and Thr632Ile, Asp633Glu) and the second extracellular loop (Ile568Thr). One mutation was found in the extracellular TSHR domain (Ser281Asn). Two new TSHR mutations were identified. One involves codon 656 in the third extracellular loop (Val656Phe). The other new mutation is a 27-bp deletion in the third intracellular loop resulting in deletion of 9 amino acids at codons 613-621. Transient expression of the new TSHR mutations in COS-7 cells demonstrated their constitutive activity. No mutation was found in exons 7-10 of the gsp gene. This finding was confirmed by an allele-specific PCR for mutations in gsp codons 201 (Arg-->His, Cys) and 227 (Gln-->His, Arg). Our data indicate that constitutively activating TSHR mutations can be found in 48% of TTNs and thus currently represent the most frequent molecular mechanism known in the etiopathogenesis of TTNs. Moreover, the absence of gsp mutations in our series argues for an only minor role of these mutations in TTNs. Constitutive activation of the TSHR by a deletion in a region that might be involved in G protein coupling of the TSHR offers new insights into TSHR activation.     

Fabrication of plastic microfluid channels by imprinting methods

Microfluidic devices have been fabricated on poly(methyl methacrylate) substrates by two independent imprinting techniques. First-generation devices were fabricated using a small-diameter wire to create an impression in plastics softened by low-temperature heating. The resulting devices are limited to only simple linear channel designs but are readily produced at low cost. Second-generation devices with more complex microchannel arrangements were fabricated by imprinting the plastic substrates using an inverse three-dimensional image of the device micromachined on a silicon wafer. This micromachined template may be used repeatedly to generate devices reproducibly. Fluorescent analtyes were used to demonstrate reproducible electrophoretic injections. An immunoassay was also performed in an imprinted device as a demonstration of future applications.     

The satellite RNA of barley yellow dwarf virus-RPV is supported by beet western yellows virus in dicotyledonous protoplasts and plants

The subgroup II luteovirus barley yellow dwarf virus-RPV (BYDV-RPV) acts as a helper virus for a satellite RNA (satRPV RNA). The subgroup II luteovirus beet western yellows virus (BWYV) and the ST9-associated RNA (ST9a RNA), a BWYV-associated RNA that encodes a polymerase similar to those of subgroup I luteoviruses, were assayed for their ability to support replication of satRPV RNA. SatRPV RNA was replicated in tobacco protoplasts in the presence of BWYV RNA or a mixture of BWYV plus the ST9a RNA, but not in the presence of ST9a RNA alone. ST9a RNA stimulated BWYV RNA accumulation which, in turn, increased the accumulation of satRPV RNA. SatRPV RNA was encapsidated in BWYV capsids primarily as circular monomers, which differs from the linear monomers found in BYDV (RPV + PAV) particles. SatRPV RNA was transmitted to Capsella bursa-pastoris plants by aphids only in the presence of BWYV and ST9a RNA. SatRPV RNA reduced accumulation of both BWYV helper and ST9a nonhelper RNAs in plants but did not affect symptoms. The replication of satRPV RNA only in the presence of subgroup II luteoviral RNAs but not in the presence of RNAs with subgroup I-like polymerase genes, in both monocotyledonous and dicotyledonous hosts, suggests that the specificity determinants of satRPV RNA replication are contained within the polymerase genes of supporting viruses rather than in structural genes or host plants.