Presynaptic alpha2-receptors regulate reverse Na+/Ca2+-exchange and transmitter release in Na+-loaded peripheral sympathetic nerves

Electrical depolarisation-(2 Hz, 1 ms)-induced [3H]noradrenaline ([3H]NA) release has been measured from the isolated main pulmonary artery of the rabbit in the presence of uptake blockers (cocaine, 3 x 10(-5) M; corticosterone, 5 x 10(-5) M). Substitution of most of the external Na+ by Li+ (113 mM; [Na+]0: 25 mM) slightly potentiated the axonal stimulation-evoked release of [3H]NA in a tetrodotoxin (TTX, 10(-7) M) sensitive manner. The reverse Na+/Ca2+-exchange inhibitor KB-R7943 (3 x 10(-5) M) failed to inhibit the stimulation-evoked release of [3H]NA, but increased the resting outflow of neurotransmitter. The 'N-type' voltage-sensitive Ca2+-channel (VSCC) blocker omega-conotoxin (omega-CgTx) GVIA (10(-8) M) significantly and irreversibly inhibited the release of [3H]NA on stimulation (approximately 60-70%). The 'residual release' of NA was abolished either by TTX or by reducing external Ca2+ from 2.5 to 0.25 mM. The 'residual release' of NA was also blocked by the non-selective VSCC-blocker neomycin (3 x 10(-3) M). Correlation was obtained between the extent of VSCC-inhibition and the transmitter release-enhancing effect of presynaptic alpha2-receptor blocker yohimbine (3 x 10(-7) M). When the release of [3H]NA was blocked by omega-CgTx GVIA plus neomycin, yohimbine was ineffective. Inhibition of the Na+-pump by removal of K+ from the external medium increased both the resting and the axonal stimulation-evoked release of [3H]NA in the absence of functioning VSCCs (i.e., in the presence of neomycin and after omega-CgTx treatment). Under these conditions the stimulation-evoked release of NA was abolished either by TTX or by external Ca2+-removal (+1 mM EGTA). Similarly, external Li+ (113 mM) or the reverse Na+/Ca2+ exchange blocker KB-R7943 (3 x 10(-5) M) significantly inhibited the stimulation-induced transmitter release in 'K+-free' solution. KB-R7943 decreased the resting outflow of NA as well. Under conditions in which the Na+-pump was inhibited in the absence of functioning VSCCs, yohimbine (3 x 10(-7) M) further enhanced the release of neurotransmitter, while l-noradrenaline (l-NA, 10(-6) M), an agonist of presynaptic alpha2-receptors, inhibited it. The yohimbine-induced enhancement of NA-release was abolished by Li+-substitution and significantly inhibited by KB-R7943 application. It is concluded that after blockade of VSCCs brief depolarising pulses may reverse Na+/Ca2+-exchange and release neurotransmitter in Na+-loaded sympathetic nerves. Further, similar to that of VSCCs, the reverse Na+/Ca2+-exchange may also be regulated by presynaptic alpha2-receptors.     

Solid-phase synthesis of an N-(phenylalkyl)cinnamide library via Horner-Wadsworth-Emmons reaction

A readily automated solid-phase approach to the synthesis of diverse N-(phenylalkyl)cinnamides, analogues of the NR2B antagonist 2, is described. The procedure utilizes polymer supported N-(phenylalkyl)amines, (diethylphosphono)acetic acid and a wide range of commercially available hydroxybenzaldehydes. The key step, a Horner-Wadsworth-Emmons reaction is achieved under mild conditions and was found to be general for a large number of benzaldehydes. A 225-member focused library was synthesized using a Tecan Combitec synthesizer.     

Integrative analysis of cell cycle control in budding yeast

The adaptive responses of a living cell to internal and external signals are controlled by networks of proteins whose interactions are so complex that the functional integration of the network cannot be comprehended by intuitive reasoning alone. Mathematical modeling, based on biochemical rate equations, provides a rigorous and reliable tool for unraveling the complexities of molecular regulatory networks. The budding yeast cell cycle is a challenging test case for this approach, because the control system is known in exquisite detail and its function is constrained by the phenotypic properties of >100 genetically engineered strains. We show that a mathematical model built on a consensus picture of this control system is largely successful in explaining the phenotypes of mutants described so far. A few inconsistencies between the model and experiments indicate aspects of the mechanism that require revision. In addition, the model allows one to frame and critique hypotheses about how the division cycle is regulated in wild-type and mutant cells, to predict the phenotypes of new mutant combinations, and to estimate the effective values of biochemical rate constants that are difficult to measure directly in vivo.     

Servers for sequence-structure relationship analysis and prediction

We describe several algorithms and public servers that were developed to analyze and predict various features of protein structures. These servers provide information about the covalent state of cysteine (CYSREDOX), as well as about residues involved in non-covalent cross links that play an important role in the structural stability of proteins (SCIDE and SCPRED). We also discuss methods and servers developed to identify helical transmembrane proteins from large databases and rough genomic data, including two of the most popular transmembrane prediction methods, DAS and HMMTOP. Several biologically interesting applications of these servers are also presented. The servers are available through http://www.enzim.hu/servers.html.     

The new TNM classification of malignant melanoma

The identification of increasingly powerful prognostic factors has led to sequential modifications of the cutaneous melanoma staging system. The American Joint Committee on Cancer (AJCC) recently proposed major revision of tumor node metastasis (TNM) categories and stage groupings for melanoma. The authors summarize the main characteristics of this new TNM classification of malignant melanoma. The importance of the novel technique - sentinel node biopsy - in the management of malignant melanoma is discussed.     

Subcellular localization and N-glycosylation of human ABCC6, expressed in MDCKII cells

Mutations in the gene coding for a human ABC transporter protein, ABCC6 (MRP6), are responsible for the development of pseudoxanthoma elasticum. Here, we demonstrate that human ABCC6, when expressed by retroviral transduction in polarized mammalian (MDCKII) cells, is exclusively localized to the basolateral membrane. The human ABCC6 in MDCKII cells was found to be glycosylated, in contrast to the underglycosylated form of the protein, as expressed in Sf9 cells. In order to localize the major glycosylation site(s) in ABCC6, we applied limited proteolysis on the fully glycosylated and underglycosylated forms, followed by immunodetection with region-specific antibodies for ABCC6. Our results indicate that Asn15, which is located in the extracellular N-terminal region of human ABCC6, is the only N-glycosylation site in this protein. The polarized mammalian expression system characterized here provides a useful tool for further examination of routing, glycosylation, and function of the normal and pathological variants of human ABCC6.     

Effect of 2,4-dichlorophenol on DPPC/water liposomes studied by X-ray and freeze-fracture electron microscopy

The effect of 2,4-dichlorophenol (DCP) was studied on the fully hydrated 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC)--water liposomes. The structure and the thermotropic phase behaviour of the liposomes was examined in the presence of DCP (DCP/DPPC molar ratio, varied from 2x10(-2) up to 1) using small- and wide-angle X-ray scattering (SAXS, WAXS) and freeze-fracture electron microscopy. The structural behaviour of the DPPC/DCP/water system was strongly dependent on the concentration of the DCP. In the pretransition range the DCP molecules (at 2x10(-2) DCP/DPPC molar ratio) induced the interdigitated phase beside the parent (gel and rippled gel) phases, locally which can be form at higher DCP concentration. When the DCP/DPPC molar ratio was increased the pretransition disappeared and the main transition was shifted to lower temperatures. In the molar ratio range from 2x10(-1) up to 5x10(-1), a coexistence of different phases was observed in the wide temperature range from 20 up to 40 degrees C. With a further increase of the DCP/DPPC molar ratio (6x10(-1) to 1) only the interdigitated gel phase occurred below 25 degrees C. A schematic phase diagram of DPPC/DCP/water system was constructed to summarise the results.     

Cost-effective PET investigations in oncology

The authors have reviewed the financial considerations of oncological FDG PET examinations by the guidelines of the Health Care Financing Administration (USA). By critical assessment of large number of clinical investigations,the cost-effectiveness of FDG PET scans has been confirmed in the following cases: differential diagnosis of solitary pulmonary nodule, diagnosis,staging and restaging of non-small cell lung cancer, colorectal cancer, malignant lymphomas, melanoma malignum, esophageal neoplasms and cancers of the head and neck. The role of this method in breast cancer is currently under intensive investigation. Due to the correct staging, PET examinations in these indications enable the clinicians to choose the optimal treatment ensuring the maximum probability of recovery and being cost-effective as unnecessary medical interventions become avoidable.     

Ribozyme inhibition of alphavirus replication

A model system to examine the expression and antiviral activity of trans-acting ribozymes in mammalian cells has been developed and evaluated. Hairpin ribozymes were engineered to cleave a specific site, identified by a combinatorial activity-based selection method, within genomic and subgenomic RNA species of Sindbis virus. Transiently transfected cells expressed moderate levels of ribozyme (approximately 50,000 molecules/cell) with predominant nuclear localization and a short half-life (23 min). Stable cell lines expressed ribozymes at modest levels (approximately 2,000 molecules/cell). Ribozyme-mediated RNA cleavage activity was detected in cell extracts. Clonal cell lines were challenged with recombinant Sindbis virus, and viral replication was examined using plaque formation and green fluorescent protein assays. Significant inhibition of viral replication was observed in cells expressing the active antiviral ribozyme, and lower levels of inhibition in control cells expressing inactive or irrelevant ribozymes. These findings are consistent with a model in which inhibition of viral replication occurs via ribozyme cleavage of viral RNAs, suggesting that ribozymes may represent useful antiviral agents.