bluuebunny/crossref_metadata_2025 huggingface dataset:
Building youth–adult partnerships for community change: Lessons from the Youth Leadership Institute
Authors: Libby Margaret , Rosen Matt , Sedonaen Maureen
Published: November 2004

This article explores the way one youth leadership development organization has used youth–adult partnerships (Y‐APs) as a practice to support youth participation in community‐change efforts in the San Francisco Bay Area and throughout California. The authors describe how Y‐APs are used in two principal areas of the Youth Leadership Institute's work: training and philanthropy. The authors also present a set of lessons learned through over 12 years of Y‐AP practice. Based on this experience, they highlight the importance of organizational pathways for leadership development, the necessity of advance preparation by youth and adults, the need to moderate program intensity, and the difficulty of sustaining Y‐APs in a resource‐scarce environment. © 2005 Wiley Periodicals, Inc. J Comm Psychol 33: 111–120, 2005.
Developing social capital through participation in organized youth programs: Qualitative insights from three programs
Authors: Jarrett Robin L. , Sullivan Patrick J. , Watkins Natasha D.
Published: November 2004

Organized youth programs can serve as a context in which youth are connected to resource‐bearing adults in the community who promote the development of social capital. This article explores the process of how this happens and what types of resources are gained by youth. Qualitative interviews were conducted with adolescents in three youth programs over a three‐ to four‐month period. Two key findings emerged. First, relationships with community adults were found to develop in stages, with youth moving from a stage of suspicion and distrust, to a stage of facilitated contact, to a stage of meaningful connection. Second, these relationships provided youth with access to adult resources, such as information, assistance, exposure to adult worlds, support, and encouragement. The three programs facilitated this process of social capital development by linking youth to suitable adults, structuring youth–adult activities around common goals, and coaching youth on these interactions. © 2005 Wiley Periodicals, Inc. J Comm Psychol 33: 41–55, 2005.
Metastability of
Helicobacter pylori bab
adhesin genes and dynamics in Lewis b antigen binding
Authors: Bäckström Anna , Lundberg Carina , Kersulyte Dangeruta , Berg Douglas E. , Borén Thomas , Arnqvist Anna
Published: November 2004

Heterogeneity among
Helicobacter pylori
strains in gastric epithelial adherence is postulated to contribute to pathogen fitness in the physiologically diverse human population.
H. pylori
adherence to ABO and Lewis b (Leb) blood group antigens in the human stomach is mediated by the blood group antigen-binding adhesin BabA. Approximately 70% of Swedish and U.S.
H. pylori
clinical isolates exhibit Leb binding, but here we show that the
babA
gene is present in each of 10 Leb-nonbinding strains. Fluorescence microscopy identified occasional bacterial cells with a Leb-binding phenotype in populations of Leb-nonbinding strains. Thus, nonbinding seemed to be a metastable phenotype. To model metastable transition into the virulence-associated Leb-binding mode, Leb-binding clones were isolated from nonadherent strains by panning with Leb-magnetic beads and characterized. Strain 17875 has two
babA
genes,
babA1
(silent) and
babA2
(expressed). We found that a
babA2
-cam derivative of strain 17875 regained Leb binding by recombination of the formerly silent
babA1
gene into the expressed and partially homologous
babB
locus. The chimeric BabB/A adhesin binds Leb with an affinity similar to that of wild-type BabA adhesin, but its expression level was lower and was subject to phase variation through slipped-strand mispairing. Equivalent results were obtained with strain NCTC11638. We propose that adhesin metastability and heterogeneity contributes to bacterial fitness and results in some clones having potential for periodic activation and deactivation of virulence appropriate for intensity of the host response to infection.
Correction of kinetic and stability defects by tetrahydrobiopterin in phenylketonuria patients with certain phenylalanine hydroxylase mutations
Authors: Erlandsen Heidi , Pey Angel L. , Gámez Alejandra , Pérez Belén , Desviat Lourdes R. , Aguado Cristina , Koch Richard , Surendran Sankar , Tyring Stephen , Matalon Reuben , Scriver Charles R. , Ugarte Magdalena , Martínez Aurora , Stevens Raymond C.
Published: November 2004

Phenylketonuria patients harboring a subset of phenylalanine hydroxylase (PAH) mutations have recently shown normalization of blood phenylalanine levels upon oral administration of the PAH cofactor tetrahydrobiopterin [(6
R
)-
l
-
erythro
-5,6,7,8-tetrahydrobiopterin (BH
4
)]. Several hypotheses have been put forward to explain BH
4
responsiveness, but the molecular basis for the corrective effect(s) of BH
4
has not been understood. We have investigated the biochemical, kinetic, and structural changes associated with BH
4
-responsive mutations (F39L, I65T, R68S, H170D, E178G, V190A, R261Q, A300S, L308F, A313T, A373T, V388M, E390G, P407S, and Y414C). The biochemical and kinetic characterization of the 15 mutants studied points toward a multifactorial basis for the BH
4
responsiveness; the mutants show residual activity (>30% of WT) and display various kinetic defects, including increased
K
m
(BH
4
) and reduced cooperativity of substrate binding, but no decoupling of cofactor (BH
4
) oxidation. For some, BH
4
seems to function through stabilization and protection of the enzyme from inactivation and proteolytic degradation. In the crystal structures of a phenylketonuria mutant, A313T, minor changes were seen when compared with the WT PAH structures, consistent with the mild effects the mutant has upon activity of the enzyme both
in vitro
and
in vivo
. Truncations made in the A313T mutant PAH form revealed that the N and C termini of the enzyme influence active site binding. Of fundamental importance is the observation that BH
4
appears to increase Phe catabolism if at least one of the two heterozygous mutations has any residual activity remaining.
Dynamical resonance can account for seasonality of influenza epidemics
Authors: Dushoff Jonathan , Plotkin Joshua B. , Levin Simon A. , Earn David J. D.
Published: November 2004

Influenza incidence exhibits strong seasonal fluctuations in temperate regions throughout the world, concentrating the mortality and morbidity burden of the disease into a few months each year. The cause of influenza's seasonality has remained elusive. Here we show that the large oscillations in incidence may be caused by undetectably small seasonal changes in the influenza transmission rate that are amplified by dynamical resonance.
Synthesis of galmic: A nonpeptide galanin receptor agonist
Authors: Ceide Susana Conde , Trembleau Laurent , Haberhauer Gebhard , Somogyi Laszlo , Lu Xiaoying , Bartfai Tamas , Rebek Julius
Published: November 2004

Galanin is a neuropeptide with a wide variety of biological functions. Few nonpeptide ligands, capable of activating galanin receptors, are available today. Based on known pharmacophores of galanin and the tripeptidomimetic galnon, a combinatorial library was formulated, synthesized, and screened against the galanin receptor. An active compound, galmic, was identified and testedin vitroandin vivofor its affinity and efficacy at galanin receptors. The present work describes the total synthesis of galmic, the synthesis of its oxazole precursors, the coupling of the building blocks into a linear trimer, and the macrolactamization reaction.
Halogen bonds in biological molecules
Authors: Auffinger Pascal , Hays Franklin A. , Westhof Eric , Ho P. Shing
Published: November 2004

Short oxygen–halogen interactions have been known in organic chemistry since the 1950s and recently have been exploited in the design of supramolecular assemblies. The present survey of protein and nucleic acid structures reveals similar halogen bonds as potentially stabilizing inter- and intramolecular interactions that can affect ligand binding and molecular folding. A halogen bond in biomolecules can be defined as a short CX···OYinteraction (CXis a carbon-bonded chlorine, bromine, or iodine, and OYis a carbonyl, hydroxyl, charged carboxylate, or phosphate group), where theX···O distance is less than or equal to the sums of the respective van der Waals radii (3.27 Å for Cl···O, 3.37Å for Br···O, and 3.50 Å for I···O) and can conform to the geometry seen in small molecules, with the CX···O angle ≈165° (consistent with a strong directional polarization of the halogen) and theX···OYangle ≈120°. Alternative geometries can be imposed by the more complex environment found in biomolecules, depending on which of the two types of donor systems are involved in the interaction: (i) the lone pair electrons of oxygen (and, to a lesser extent, nitrogen and sulfur) atoms or (ii) the delocalized π -electrons of peptide bonds or carboxylate or amide groups. Thus, the specific geometry and diversity of the interacting partners of halogen bonds offer new and versatile tools for the design of ligands as drugs and materials in nanotechnology.
The human Rad9–Rad1–Hus1 checkpoint complex stimulates flap endonuclease 1
Authors: Wang Wensheng , Brandt Patrick , Rossi Marie L. , Lindsey-Boltz Laura , Podust Vladimir , Fanning Ellen , Sancar Aziz , Bambara Robert A.
Published: November 2004

The toroidal damage checkpoint complex Rad9–Rad1–Hus1 (9-1-1) has been characterized as a sensor of DNA damage. Flap endonuclease 1 (FEN1) is a structure-specific nuclease involved both in removing initiator RNA from Okazaki fragments and in DNA repair pathways. FEN1 activity is stimulated by proliferating cell nuclear antigen (PCNA), a toroidal sliding clamp that acts as a platform for DNA replication and repair complexes. We show that 9-1-1 also binds and stimulates FEN1. Stimulation is observed on a variety of flap, nick, and gapped substrates simulating repair intermediates. Blocking 9-1-1 entry to the double strands prevents a portion of the stimulation. Like PCNA stimulation, 9-1-1 stimulation cannot circumvent the tracking mechanism by which FEN1 enters the substrate; however, 9-1-1 does not substitute for PCNA in the stimulation of DNA polymerase β. This suggests that 9-1-1 is a damage-specific activator of FEN1.
Structural analysis of the inactive state of the
Escherichia coli
DNA polymerase clamp-loader complex
Authors: Kazmirski Steven L. , Podobnik Marjetka , Weitze Tanya F. , O'Donnell Mike , Kuriyan John
Published: November 2004

Clamp-loader complexes are heteropentameric AAA
+
ATPases that load sliding clamps onto DNA. The structure of the nucleotide-free
Escherichia coli
clamp loader had been determined previously and led to the proposal that the clamp-loader cycles between an inactive state, in which the ATPase domains form a closed ring, and an active state that opens up to form a “C” shape. The crystal structure was interpreted as being closer to the active state than the inactive state. The crystal structure of a nucleotide-bound eukaryotic clamp loader [replication factor C (RFC)] revealed a different and more tightly packed spiral organization of the ATPase domains, raising questions about the significance of the conformation seen earlier for the bacterial clamp loader. We describe crystal structures of the
E
.
coli
clamp-loader complex bound to the ATP analog ATPγS (at a resolution of 3.5 Å) and ADP (at a resolution of 4.1 Å). These structures are similar to that of the nucleotide-free clamp-loader complex. Only two of the three functional ATP-binding sites are occupied by ATPγS or ADP in these structures, and the bound nucleotides make no interfacial contacts in the complex. These results, along with data from isothermal titration calorimetry, molecular dynamics simulations, and comparison with the RFC structure, suggest that the more open form of the
E
.
coli
clamp loader described earlier and in the present work corresponds to a stable inactive state of the clamp loader in which the ATPase domains are prevented from engaging the clamp in the highly cooperative manner seen in the fully ATP-loaded RFC-clamp structure.
Molecular modeling of family GH16 glycoside hydrolases: Potential roles for xyloglucan transglucosylases/hydrolases in cell wall modification in the poaceae
Authors: Strohmeier Marco , Hrmova Maria , Fischer Markus , Harvey Andrew J. , Fincher Geoffrey B. , Pleiss Jürgen
Published: November 2004

Family GH16 glycoside hydrolases can be assigned to five subgroups according to their substrate specificities, including xyloglucan transglucosylases/hydrolases (XTHs), (1,3)‐β‐galactanases, (1,4)‐β‐galactanases/κ‐carrageenases, “nonspecific” (1,3/1,3;1,4)‐ β‐d‐glucan endohydrolases, and (1,3;1,4)‐β‐d‐glucan endohydrolases. A structured family GH16 glycoside hydrolase database has been constructed (http://www.ghdb.uni‐stuttgart.de) and provides multiple sequence alignments with functionally annotated amino acid residues and phylogenetic trees. The database has been used for homology modeling of seven glycoside hydrolases from the GH16 family with various substrate specificities, based on structural coordinates for (1,3;1,4)‐β‐d‐glucan endohydrolases and a κ‐carrageenase. In combination with multiple sequence alignments, the models predict the three‐dimensional (3D) dispositions of amino acid residues in the substrate‐binding and catalytic sites of XTHs and (1,3/1,3;1,4)‐β‐d‐glucan endohydrolases; there is no structural information available in the databases for the latter group of enzymes. Models of the XTHs, compared with the recently determined structure of a Populus tremulos × tremuloides XTH, reveal similarities with the active sites of family GH11 (1,4)‐β‐d‐xylan endohydrolases. From a biological viewpoint, the classification, molecular modeling and a new 3D structure of the P. tremulos × tremuloides XTH establish structural and evolutionary connections between XTHs, (1,3;1,4)‐β‐d‐glucan endohydrolases and xylan endohydrolases. These findings raise the possibility that XTHs from higher plants could be active not only on cell wall xyloglucans, but also on (1,3;1,4)‐β‐d‐glucans and arabinoxylans, which are major components of walls in grasses. A role for XTHs in (1,3;1,4)‐β‐d‐glucan and arabinoxylan modification would be consistent with the apparent overrepresentation of XTH sequences in cereal expressed sequence tags databases.
Solvation and the hidden thermodynamics of a zinc finger probed by nonstandard repair of a protein crevice
Authors: Lachenmann Marcel J. , Ladbury John E. , Qian Xiuqi , Huang Kun , Singh Rupinder , Weiss Michael A.
Published: November 2004

The classical Zn finger contains a phenylalanine at the crux of its three architectural elements: a β‐hairpin, an α‐helix, and a Zn2+‐binding site. Surprisingly, phenylalanine is not required for high‐affinity Zn2+ binding, but instead contributes to the specification of a precise DNA‐binding surface. Substitution of phenylalanine by leucine leads to a floppy but native‐like structure whose Zn affinity is maintained by marked entropy–enthalpy compensation (Δ ΔH −8.3 kcal/mol and −TΔ ΔS 7.7 kcal/mol). Phenylalanine and leucine differ in shape, size, and aromaticity. To distinguish which features correlate with dynamic stability, we have investigated a nonstandard finger containing cyclohexanylalanine at this site. The structure of the nonstandard finger is similar to that of the native domain. The cyclohexanyl ring assumes a chair conformation, and conformational fluctuations characteristic of the leucine variant are damped. Although the nonstandard finger exhibits a lower affinity for Zn2+ than does the native domain (Δ ΔG −1.2 kcal/mol), leucine‐associated perturbations in enthalpy and entropy are almost completely attenuated (Δ ΔH −0.7 kcal/mol and −TΔ ΔS −0.5 kcal/mol). Strikingly, global changes in entropy (as inferred from calorimetry) are in each case opposite in sign from changes in configurational entropy (as inferred from NMR). This seeming paradox suggests that enthalpy–entropy compensation is dominated by solvent reorganization rather than nominal molecular properties. Together, these results demonstrate that dynamic and thermodynamic perturbations correlate with formation or repair of a solvated packing defect rather than type of physical interaction (aromatic or aliphatic) within the core.
Infrequent cavity‐forming fluctuations in HPr from Staphylococcus carnosus revealed by pressure‐ and temperature‐dependent tyrosine ring flips
Authors: Hattori Mineyuki , Li Hua , Yamada Hiroaki , Akasaka Kazuyuki , Hengstenberg Wolfgang , Gronwald Wolfram , Kalbitzer Hans Robert
Published: November 2004

Infrequent structural fluctuations of a globular protein is seldom detected and studied in detail. One tyrosine ring of HPr from Staphylococcus carnosus, an 88‐residue phosphocarrier protein with no disulfide bonds, undergoes a very slow ring flip, the pressure and temperature dependence of which is studied in detail using the on‐line cell high‐pressure nuclear magnetic resonance technique in the pressure range from 3 MPa to 200 MPa and in the temperature range from 257 K to 313 K. The ring of Tyr6 is buried sandwiched between a β‐sheet and α‐helices (the water‐accessible area is less than 0.26 nm2), its hydroxyl proton being involved in an internal hydrogen bond. The ring flip rates101∼105 s−1 were determined from the line shape analysis of Hδ1, δ2 and Hε1,ε2 of Tyr6, giving an activation volume ΔV‡ of 0.044 ± 0.008 nm3 (27 mL mol−1), an activation enthalpy ΔH‡ of 89 ± 10 kJ mol−1, and an activation entropy ΔS‡ of 16 ± 2 JK−1 mol−1. The ΔV‡ and ΔH‡ values for HPr found previously for Tyr and Phe ring flips of BPTI and cytochrome c fall within the range of ΔV‡ of 28 to 51 mL mol−1 and ΔH‡ of 71 to 155 kJ mol−1. The fairly common ΔV‡ and ΔH‡ values are considered to represent the extra space or cavity required for the ring flip and the extra energy required to create a cavity, respectively, in the core part of a globular protein. Nearly complete cold denaturation was found to take place at 200 MPa and 257 K independently from the ring reorientation process.
Specific recognition of a dsDNA sequence motif by an immunoglobulin VH homodimer
Authors: Jin Hulin , Sepúlveda Jorge , Burrone Oscar R.
Published: November 2004

Anti‐DNA antibodies have the potential to be applied in vast fields of fundamental as well as medical research. They are found in autoimmune diseases, such as systemic lupus erythemotosus. In most cases, anti‐dsDNA antibodies do not present sequence specificity and are of low affinity. The dominant role of VH domains in DNA recognition induced us to search for binders based on VH dimers (VHD), previously reported to bind different protein antigens. We screened a phage displayed homo‐VHD library against a 19‐bp dsDNA sequence. A sequence‐specific binder was selected, which recognizes the terminal located CTGC motif with a Kd of 250 nM. Association of the two identical VH domains of the molecule was shown to be essential for binding.
Biochemical properties of V91G calmodulin: A calmodulin point mutation that deregulates muscle contraction in Drosophila
Authors: Wang Bo , Martin Stephen R. , Newman Rhonda A. , Hamilton Susan L. , Shea Madeline A. , Bayley Peter M. , Beckingham Kathleen M.
Published: November 2004

A mutation (Cam7) to the single endogenous calmodulin gene of Drosophila generates a mutant protein with valine 91 changed to glycine (V91G D‐CaM). This mutation produces a unique pupal lethal phenotype distinct from that of a null mutation. Genetic studies indicate that the phenotype reflects deregulation of calcium fluxes within the larval muscles, leading to hypercontraction followed by muscle failure. We investigated the biochemical properties of V91G D‐CaM. The effects of the mutation on free CaM are minor: Calcium binding, and overall secondary and tertiary structure are indistinguishable from those of wild type. A slight destabilization of the C‐terminal domain is detectable in the calcium‐free (apo‐) form, and the calcium‐bound (holo‐) form has a somewhat lower surface hydrophobicity. These findings reinforce the indications from the in vivo work that interaction with a specific CaM target(s) underlies the mutant defects. In particular, defective regulation of ryanodine receptor (RyR) channels was indicated by genetic interaction analysis. Studies described here establish that the putative CaM binding region of the Drosophila RyR (D‐RyR) binds wild‐type D‐CaM comparably to the equivalent CaM‐RyR interactions seen for the mammalian skeletal muscle RyR channel isoform (RYR1). The V91G mutation weakens the interaction of both apo‐ and holo‐D‐CaM with this binding region, and decreases the enhancement of the calcium‐binding affinity of CaM that is detectable in the presence of the RyR target peptide. The predicted functional consequences of these changes are consonant with the in vivo phenotype, and indicate that D‐RyR is one, if not the major, target affected by the V91G mutation in CaM.
Cognitive Approaches to Schizophrenia: Theory and Therapy
Authors: Beck Aaron T. , Rector Neil A.
Published: November 2004

A theoretical analysis of schizophrenia based on a cognitive model integrates the complex interaction of predisposing neurobiological, environmental, cognitive, and behavioral factors with the diverse symptomatology. The impaired integrative function of the brain, as well as the domain-specific cognitive deficits, increases the vulnerability to aversive life experiences, which lead to dysfunctional beliefs and behaviors. Symptoms of disorganization result not only from specific neurocognitive deficits but also from the relative paucity of resources available for maintaining a set, adhering to rules of communication, and inhibiting intrusion of inappropriate ideas. Delusions are analyzed in terms of the interplay between active cognitive biases, such as external attributions, and resource-sparing strategies such as jumping to conclusions. Similarly, the content of hallucinations and the delusions regarding their origin and characteristics may be understood in terms of biased information processing. The interaction of neurocognitive deficits, personality, and life events leads to the negative symptoms characterized by negative social and performance beliefs, low expectancies for pleasure and success, and a resource-sparing strategy to conserve limited psychological resources. The comprehensive conceptualization creates the context for targeted psychological treatments.
Essential role of p53 in silica-induced apoptosis
Authors: Wang Liying , Bowman Linda , Lu Yongju , Rojanasakul Yon , Mercer Robert R. , Castranova Vince , Ding Min
Published: November 2004

Occupational exposure to mineral dusts, such as silica, has been associated with progressive pulmonary inflammation, lung cancer, and fibrosis. However, the mechanisms involved in this process are poorly understood. Because p53 is a key transcription factor regulating many important apoptosis-related genes, we hypothesized that p53 may play a key role in silica-induced apoptosis and that abnormal regulation of p53 by silica may contribute to development of lung cancer as well as silicosis. We used both in vitro and in vivo studies to test this hypothesis. Treatment of JB6 cells carrying a p53-luciferase reporter plasmid with silica caused dose-dependent p53 transactivation. Western blot indicates that silica not only stimulated p53 protein expression but also caused p53 phosphorylation at Ser392. TUNEL and DNA fragmentation analysis show that silica caused apoptosis in both JB6 cells and wild-type p53 ( p53+/+) fibroblasts but not in p53-deficient ( p53−/−) fibroblasts. Similar results were obtained by in vivo studies. Intratracheal instillation of mice with silica induced apoptosis in the lung of p53+/+ mice, whereas this induction was significantly inhibited in p53−/− mice. Confocal image analysis indicates that most apoptotic cells induced by silica were alveolar macrophages. These results demonstrate for the first time that silica induces p53 transactivation via induction of p53 protein expression and phosphorylation of p53 protein and that p53 plays a crucial role in the signal transduction pathways of silica-induced apoptosis. This finding may provide an important link in understanding the molecular mechanisms of silica-induced carcinogenesis and pathogenesis in the lung.
Capsazepine, a vanilloid antagonist, abolishes tonic responses induced by 20-HETE on guinea pig airway smooth muscle
Authors: Rousseau É , Cloutier Martin , Morin Caroline , Proteau Sonia
Published: November 2004

The aim of this study was to delineate the mode of action of 20-hydroxy-eicosatetraenoic acid (20-HETE) in airway smooth muscle (ASM) cells. ASM metabolizes arachidonic acid by various enzymatic pathways, including the cytochrome P-450 (CYP-450) ω-hydroxylase, which leads to the production of 20-HETE, a bronchoconstrictive eicosanoid. The present study demonstrated that 20-HETE induced concentration-dependent tonic responses in ASM, whereas transient responses were recorded in Ca2+-free solution, suggesting an intracellular Ca2+release process. 20-HETE inotropic responses were abolished by 36 μM 2-aminoethoxydiphenyl borate or 1 μM thapsigargin but were insensitive to 10 μM ryanodine, indicating that inositol triphosphate receptors likely control the release of intracellular Ca2+. Sustained tension, which required Ca2+entry, was partially blocked by 1 μM nifedipine (an L-type) and 100 μM Gd3+(a nonselective cationic channel blocker). Moreover, in the absence of selective 20-HETE receptor antagonists, 20-HETE tonic responses were inhibited in a concentration-dependent manner (0.1–10 μM) by capsazepine, a well-characterized vanilloid receptor antagonist. Capsazepine was also observed to reverse cumulative responses to 20-HETE and capsaicin, a TRPV1 agonist. In addition, capsazepine pretreatment largely modified the sustained inotropic responses to 20-HETE, suggesting that 20-HETE cross-reacted with TRPV1 receptors with a low affinity (μM) or that its specific receptor was inhibited by the vanilloid antagonist. Data obtained using RHC-80267, ONO-RS-082, and eicosatetraynoic acid, respective inhibitors of diacylglycerol-lipase, phospholipase A2, and CYP-450 ω-hydroxylase, reveal that intracellular arachidonic acid production and its 20-HETE metabolite may be responsible for the activation of nonselective cationic channels and tonic responses.
Muscle contraction-blood flow interactions during upright knee extension exercise in humans
Authors: Lutjemeier Barbara J. , Miura Akira , Scheuermann Barry W. , Koga Shunsaku , Townsend Dana K. , Barstow Thomas J.
Published: November 2004

To test for evidence of a muscle pump effect during steady-state upright submaximal knee extension exercise, seven male subjects performed seven discontinuous, incremental exercise stages (3 min/stage) at 40 contractions/min, at work rates ranging to 60–75% peak aerobic work rate. Cardiac cycle-averaged muscle blood flow (MBF) responses and contraction-averaged blood flow responses were calculated from continuous Doppler sonography of the femoral artery. Net contribution of the muscle pump was estimated by the difference between mean exercise blood flow (MBFM) and early recovery blood flow (MBFR). MBFM rose in proportion with increases in power output with no significant difference between the two methods of calculating MBF. For stages 1 and 5, MBFM was greater than MBFR; for all others, MBFM was similar to MBFR. For the lighter work rates ( stages 1–4), there was no significant difference between exercise and early recovery mean arterial pressure (MAP). During stages 5–7, MAP was significantly higher during exercise and fell significantly early in recovery. From these results we conclude that 1) at the lightest work rate, the muscle pump had a net positive effect on MBFM, 2) during steady-state moderate exercise ( stages 2–4) the net effect of rhythmic muscle contraction was neutral (i.e., the impedance due to muscle contraction was exactly offset by the potential enhancement during relaxation), and 3) at the three higher work rates tested ( stages 5–7), any enhancement to flow during relaxation was insufficient to fully compensate for the contraction-induced impedance to muscle perfusion. This necessitated a higher MAP to achieve the MBFM.
Postactivation potentiation influences differently the nonlinear summation of contractions in young and elderly adults
Authors: Baudry Stéphane , Klass Malgorzata , Duchateau Jacques
Published: November 2004

The force enhancement of a twitch after a maximal conditioning muscle contraction [i.e., postactivation potentiation (PAP)] is reduced with aging, but its influence on the summation of force in response to repetitive stimulation at different frequencies is not known. The purpose of this work was to compare the electrically evoked mechanical responses of the tibialis anterior muscle between young and elderly adults after a 6-s maximal voluntary contraction (MVC). The results showed that, immediately after the conditioning MVC, twitch torque and its maximal rate of development and relaxation were significantly enhanced in both groups, but the magnitude of potentiation was greater in young (148.0 ± 14.2, 123.7 ± 16.5, and 185.4 ± 36.5%, respectively) compared with elderly adults (87.4 ± 15.2, 63.8 ± 9.9, and 62.9 ± 11.0%, respectively). This age-related difference in potentiation of the twitch disappeared completely 1 min after the conditioning MVC. The potentiation of torque and speed-related parameters in response to two- and three-pulse trains, delivered at a constant interval of 10 ms (100 Hz), was less than for a single pulse for both groups. In young adults, the magnitude of PAP on the successive individual mechanical contributions within a train of stimuli declined progressively such that the third contribution did not differ significantly from the same contribution before the conditioning MVC. In contrast, the second and third contributions did not potentiate ( P > 0.05) in elderly adults. Although these contributions did potentiate significantly at a lower frequency of stimulation (20 Hz) in the two groups, the difference in PAP between young and elderly adults still persisted. This overall attenuation of potentiation with aging, however, appears to have a moderate influence on the decrement of the muscular performance.
An expanded latch-bridge model of protein kinase C-mediated smooth muscle contraction
Authors: Hai Chi-Ming , Kim Hak Rim
Published: November 2004

A thin-filament-regulated latch-bridge model of smooth muscle contraction is proposed to integrate thin-filament-based inhibition of actomyosin ATPase activity with myosin phosphorylation in the regulation of smooth muscle mechanics. The model included two latch-bridge cycles, one of which was identical to the four-state model as proposed by Hai and Murphy ( Am J Physiol Cell Physiol 255: C86–C94, 1988), whereas the ultraslow cross-bridge cycle has lower cross-bridge cycling rates. The model-fitted phorbol ester induced slow contractions at constant myosin phosphorylation and predicted steeper dependence of force on myosin phosphorylation in phorbol ester-stimulated smooth muscle. By shifting cross bridges between the two latch-bridge cycles, the model predicts that a smooth muscle cell can either maintain force at extremely low-energy cost or change its contractile state rapidly, if necessary. Depending on the fraction of cross bridges engaged in the ultraslow latch-bridge cycle, the model predicted biphasic kinetics of smooth muscle mechanics and variable steady-state dependencies of force and shortening velocity on myosin phosphorylation. These results suggest that thin-filament-based regulatory proteins may function as tuners of actomyosin ATPase activity, thus allowing a smooth muscle cell to have two discrete cross-bridge cycles with different cross-bridge cycling rates.
Thrombin and histamine induce stiffening of alveolar epithelial cells
Authors: Trepat Xavier , Grabulosa Mireia , Buscemi Lara , Rico Fèlix , Farré Ramon , Navajas Daniel
Published: November 2004

The mechanical properties of alveolar epithelial cells play a central role in maintaining the physical integrity of the alveolar epithelium. We studied the viscoelastic properties of alveolar epithelial cells (A549) in response to thrombin and histamine with optical magnetic twisting cytometry. Ferrimagnetic beads coated with Arg-Gly-Asp (RGD)-peptide or acetylated low-density lipoprotein were bound to cell surface receptors and subsequently twisted in an oscillatory magnetic field (0.1–100 Hz). The cell storage (G′) and loss (G″) moduli were computed from twisting torque and bead displacement. In measurements with RGD-coated beads, thrombin (0.5 U/ml) induced a rapid and sustained threefold increase in G′ and G″ at ∼100 s after challenge. Histamine (100 μM) induced a rapid but transient twofold increase in G′ and G″ with maximum values 60 s after challenge. Posttreatment with cytochalasin D abolished thrombin-induced cell stiffening. G′ increased with frequency following a power law with exponent 0.214. G″ increased proportionally to G′ up to 10 Hz but showed a steeper rise at higher frequencies. Thrombin caused a fall in the power-law exponent (0.164). In measurements with acetylated low-density lipoprotein-coated beads, minor changes (<20%) were observed in G′ and G″ after the addition of thrombin and histamine. F-actin staining revealed that thrombin and histamine induced a profound reorganization of the actin cytoskeleton at the cell periphery and formation of actin bundles. In the mechanically dynamic environment of the lung, cell stiffening induced by thrombin and histamine increases centripetal tension, which could contribute to alveolar barrier dysfunction.
Geniohyoid muscle properties and myosin heavy chain composition are altered after short-term intermittent hypoxic exposure
Authors: Pae Eung-Kwon , Wu Jennifer , Nguyen Daniel , Monti Ryan , Harper Ronald M.
Published: November 2004

Patients with obstructive sleep apnea (OSA) often exhibit fatigued or inefficient upper airway dilator and constrictor muscles; an upper airway dilator, the geniohyoid (GH) muscle, is a particular example. Intermittent hypoxia (IH) is a frequent concomitant of OSA, and it may trigger muscle fiber composition changes that are characteristic of a fatigable nature. We examined effects of short-term IH on diaphragmatic and GH muscle fiber composition and fatigue properties by exposing 24 rats to alternating 10.3% O2-balance N2 and room air every 480 s (240 s duty cycle) for a total duration of 5, 10, 15, 20, or 30 h. Sternohyoid fiber composition was also examined. Control animals were exposed to room air on the same schedule. Single-fiber analyses showed that GH muscle fiber types changed completely from myosin heavy chain (MHC) type 2A to MHC type 2B after 10 h of exposure, and the conversion was maintained for at least 30 h. Sternohyoid muscle fibers showed a delayed transition from MHC type 2A/2B to MHC type 2B. In contrast, major fiber types of the diaphragm were not significantly altered. The GH muscles showed similar tension-frequency relationships in all groups, but an increased fatigability developed, proportional to the duration of IH treatment. We conclude that short-term IH exposure alters GH muscle composition and physical properties toward more fatigable, fast-twitch types and that it may account for the fatigable upper airway fiber types found in sleep-disturbed breathing.
Theoretical and empirical derivation of cardiovascular allometric relationships in children
Authors: Sluysmans Thierry , Colan Steven D.
Published: November 2004

Basic fluid dynamic principles were used to derive a theoretical model of optimum cardiovascular allometry, the relationship between somatic and cardiovascular growth. The validity of the predicted models was then tested against the size of 22 cardiovascular structures measured echocardiographically in 496 normal children aged 1 day to 20 yr, including valves, pulmonary arteries, aorta and aortic branches, pulmonary veins, and left ventricular volume. Body surface area (BSA) was found to be a more important determinant of the size of each of the cardiovascular structures than age, height, or weight alone. The observed vascular and valvar dimensions were in agreement with values predicted from the theoretical models. Vascular and valve diameters related linearly to the square root of BSA, whereas valve and vascular areas related to BSA. The relationship between left ventricular volume and body size fit a complex model predicted by the nonlinear decrease of heart rate with growth. Overall, the relationship between cardiac output and body size is the fundamental driving factor in cardiovascular allometry.
Mit(h)ra(s) and the Myths of the Sun
Authors: Sick David
Published: November 2004

The extent of the connection between Indo-Iranian Mitra/Mithra and Roman Mithras has been vehemently debated for the last thirty years. One of the several problems in outlining the history of Mit(h)ra(s) has been the definition of the Iranian Mithra. In particular, the process by which he becomes a solar deity in the postAvestan period needs clarification. This study considers the history of Mithra with regard to solar mythology; it describes a set of myths from the traditions of two neighbors to Iran — Greece and India. In this set of myths, the Sun is the guardian of contracts and cattle; the ritual of sacrifice relates these two wards, as cattle are victims in the ritual, which may be understood as a contract between gods and humans. With this mythic system recovered from the oldest Greek and Indic texts, the history of Iranian Mithra is reviewed with the intent of interpreting that god: he has assumed the role typically assigned to the Sun in a similar mythic complex. Themes in the myth and cult of Roman Mithras are suggested for comparison.
Chronic Myelogenous Leukemia and Myeloproliferative Disease
Authors: O'Brien Stephen , Tefferi Ayalew , Valent Peter
Published: November 2004

In Section I, Dr. Stephen O’Brien reviews the latest data on the clinical use of imatinib (STI571, Gleevec, Glivec) in CML. His review focuses on the use of imatinib in newly diagnosed chronic phase patients and summarizes cytogenetic and molecular response data, as well as use of the agent at high doses and in combination with other drugs. A brief summary of the prospective international Phase III studies that are currently ongoing is also provided, and the issues of resistance and definition of suboptimal therapeutic response are also covered. Finally, therapeutic decision-making and treatment strategy are considered.

In Section II, Dr. Ayalew Tefferi considers the latest developments in the biology and therapy of myeloid metaplasia/myelofibrosis. Dr. Tefferi covers what is currently understood of the biology of the disease and reviews established therapies for the condition as well as novel agents that are being used in clinical trials. The development of optimal management strategies for the disease is considered.

In Section III, Dr. Peter Valent reviews the classification of mast cell proliferative disorders and covers the clinical and pathological presentation of this group of neoplasms. He reviews the state-of-the-art regarding the molecular biology of mastocytosis along with diagnostic criteria and novel treatment concepts.
Amyloidosis and Waldenström’s Macroglobulinemia
Authors: Gertz Morie A. , Merlini Giampaolo , Treon Steven P.
Published: November 2004

Primary systemic amyloidosis is an immunoglobulin light chain disorder that is 1/5th as common as multiple myeloma. Amyloidosis is regularly seen in the practice of a hematologist and has recently undergone major advances in terms of the ability to evaluate responses as well as new therapeutic options that were not available when this topic was covered as an education session at the American Society of Hematology meeting 5 years ago. Waldenström macroglobulinemia (WM) is rarer than amyloidosis (1500 per year WM versus 3000 per year amyloid in the US), and recent consensus panels have established the definition of the disease, the diagnostic criteria, criteria for initiation of therapy and a new classification scheme. In this session, new developments in amyloid and macroglobulinemia, from suspicion of the diagnosis to treatment, are covered.

In Section I, Dr. Morie Gertz answers four specific questions: (1) When should amyloidosis be suspected? (2) How does one heighten ones index of suspicion for amyloid? (3) How is the diagnosis confirmed and the type classified as primary? (4) What is the prognosis and how is it accurately assessed? Recent findings on cardiac biomarkers, presenting features and use of the free light chain assay are reviewed. Staging for amyloid and recently proposed criteria of response and progression are covered.

In Section II, Dr. Giampaolo Merlini comprehensively reviews therapy of amyloidosis from the use of standard melphalan/prednisone to the recently described standard dose therapies including dexamethasone, thalidomide/dexamethasone, melphalan/dexamethasone and IV melphalan/dexamethasone. An extensive discussion of the role of high-dose therapy with stem cell reconstitution follows and includes patient selection, predictors of immediate morbidity and mortality, and survival expectation. Finally, a therapeuitc strategy is proposed.

In Section III, Drs. Steven Treon and Giampaolo Merlini review the most current information on WM. The consensus panel results and recommendations of the clinical pathologic definition of WM, the prognostic markers and the indications to initiate therapy in WM, the uniform response criteria in WM and available treatments for the disease are reviewed. Drs. Treon and Merlini cover recently published treatment protocols that use rituximab, purine nucleoside analogs, and alkylating agents. The current data on thalidomide, alpha interferon, and high-dose therapy are also covered.
Marrow Failure
Authors: Bagby Grover C. , Lipton Jeffrey M. , Sloand Elaine M. , Schiffer Charles A.
Published: November 2004

New discoveries in cell biology, molecular biology and genetics have unveiled some of the pathophysiological mysteries of some of the bone marrow failure syndromes. Many of these discoveries have revealed why these syndromes show so much clinical overlap and some hold the potential for influencing the development of new therapies. In children and adults with pancytopenia and hypoplastic bone marrows proper differential diagnosis requires that some attention be directed toward defining molecular and cellular pathogenetic mechanisms because, once identified, some of these mechanisms will clearly suggest rational therapeutic approaches, treatment options that should be avoided, or both.

In Section I, Drs. Jeffrey Lipton and Grover Bagby review the approach to diagnosis and management of patients with the inherited bone marrow failure syndromes, Fanconi anemia, dyskeratosis congenita, Diamond-Blackfan anemia, and the Shwachman-Diamond syndrome. Extraordinary progress has been made in identifying the genes bearing pathogenetically relevant mutations in these disorders, but slower progress has been made in defining the precise functions of the proteins these genes encode in normal cells, in part because it is increasingly obvious that the proteins are multifunctional. In practice, it is clear that in patients with dyskeratosis congenita and Fanconi anemia, the diagnosis must be considered not only in children but in adults as well.

In Section II, Dr. Elaine Sloand outlines a very practical and evidence-based approach to diagnosis and management of acquired hypoplastic states emphasizing overlap between non-clonal and clonal hematopoiesis is such conditions. The pathogenesis of T lymphocyte–mediated marrow failure is presented as a clear-cut rationale for use of immunosuppressive therapy and stem cell transplantation. Practical management of patients with refractory disease with and without evidence of clonal evolution (either paroxysmal nocturnal hemoglobinuria [PNH] or myelodysplasia [MDS]) is presented.

In Section III, the challenge of hypoplastic MDS is reviewed by Dr. Charles Schiffer. After reviewing the most up-to-date classification scheme, therapeutic options are reviewed, focusing largely on agents that have most recently shown some promising activity, including DNA demethylating agents, thalidomide and CC5013, arsenic trioxide, and immunosuppressive therapy. Here are also outlined the rationale and the indications for choosing allogeneic bone marrow transplantation, the only therapy with known curative potential.
Sickle Cell Disease
Authors: Buchanan George R. , DeBaun Michael R. , Quinn Charles T. , Steinberg Martin H.
Published: November 2004

Much progress has been made during the past several decades in gaining understanding about the natural history of sickle cell disease and management approaches aimed at treating or even preventing certain disease complications. The characterization of the human genome now offers the opportunity to understand relationships regarding how gene polymorphisms as well as how environmental factors affect the sickle cell disease phenotype, i.e., the individual patient’s overall clinical severity as well as their specific organ function. This chapter explores some of these recent advances in knowledge.

In Section I, Dr. Michael DeBaun characterizes the problem of silent stroke in sickle cell disease, comparing and contrasting its clinical and neuroimaging features with overt stroke. Combined, these events affect virtually 40% of children with sickle cell anemia. New understanding of risk factors, associated clinical findings, and imaging technologies are impacting substantially on treatment options. The appreciable cognitive dysfunction and other sequelae of silent infarct demand more effective treatments and ultimate prevention.

In Section II, Dr. Charles Quinn addresses the conundrum of why some patients with sickle cell disease do well whereas others fare poorly. Some risk factors have been known for years, based upon careful study of hundreds of patients by the Cooperative Study for Sickle Cell Disease and investigators studying the Jamaican newborn cohort. Other prognostic measures have only recently been defined. Dr. Quinn devotes special attention to stroke and chest syndrome as organ-related complications but also describes attempts to measure overall disease severity and to predict survival. Recently, investigators have attempted to predict factors responsible for early mortality in children and following onset of pulmonary hypertension in adults.

In Section III, Dr. Martin Steinberg reviews pharmacologic approaches to sickle cell disease and the rationale for their use. In addition to the inhibition of hemoglobin S polymerization, newer targets have been defined during the past one to two decades. These include the erythrocyte membrane, changes in the red cell intracellular content (especially loss of water), endothelial injury, and free radical production. Hydroxyurea treatment attracted the greatest interest, but many uncertainties remain about its long-term benefits and toxicities. Newer “anti-sickling” agents such as decitabine and short-chain fatty acids also receive attention. Prevention of red cell dehydration, “anti-endothelial” therapy, and marshaling the potentially beneficial effects of nitric oxide are other new and exciting approaches.