Time-dependent changes of calcium influx and efflux rates in rabbit skeletal muscle sarcoplasmic reticulum

Unfractionated and low buoyant density sarcoplasmic reticulum vesicles released calcium spontaneously after ATP- or acetyl phosphate-supported calcium uptake when internal Ca²⁺ was stabilized by the use of 50 mM phosphate as calcium-precipitating anion. This spontaneous calcium release could not be attributed to falling Ca²⁺ concentration outside the vesicles (Ca₀²⁺), substrate depletion, ADP accumulation, nonspecific membrane deterioration or the attainment of a high vesicular calcium content. Instead, spontaneous calcium release was directly proportional to Ca₀²⁺ at the time that calcium content was maximal. A causal relationship between high Ca₀²⁺ and spontaneous calcium release was suggested by the finding that elevation of Ca₀²⁺ from less than 1 μM to 3–5 μM increased the rate and extent of calcium release.The spontaneous calcium release was due both to acceleration of calcium efflux and slowing of calcium influx that was not accompanied by a significant change in the rate of ATP hydrolysis. Neither reversal of the transmembrane KCl gradient nor incubation with cation and proton ionophores abolished the spontaneous calcium release. The persistence of calcium release under conditions where the membrane was permeable to both anions and cations makes it unlikely that this phenomenon is due to a changing transmembrane potential.     

Simulation of grana stacking in a model membrane system. Mediation by a purified light-harvesting pigment-protein complex from chloroplasts

An isolated light-harvesting pigment-protein complex contains polypeptides which bind chlorophyll a and b. The individual complexes can be purified from detergent-solubilized membranes. The isolated light-harvesting complex, when dialyzed to remove detergents, was examined by freeze-fracture electron microscopy. The material consisted of planar sheets of 80-Å subunits which interacted via an edge-to-edge contact. Addition of cations caused the planar light-harvesting complex sheets to become tightly appressed in multilamellar stacks, with distinct subunits still visible within each lamellar sheet. A transition of particle organization from random to crystalline occurred in parallel with the cation-induced lamellar association. Treatment of the dialyzed light-harvesting complex subunits with low levels of the proteolytic enzyme trypsin removed a 2000 molecular weight segment of the major polypeptide of the light-harvesting complex and blocked all subsequent cation-induced changes in structural organization of the isolated light-harvesting complex lamellar sheets.To gain further evidence for mechanisms of cation effects upon the organization of the light-harvesting complex in native membranes, the light-harvesting complex was incorporated into uncharged (phosphatidylcholine) lipid vesicles. The protein complexes spanned the lipid bilayer and were arranged in either a random pattern or in hexagonal crystalline lattices. Addition of either monovalent or divalent cations to ‘low-salt’ (20 mM monovalent cation) vesicles containing light-harvesting complex caused extensive regions of membrane appression to appear. It is concluded that this cation-induced membrane appression is mediated by surface-exposed segments of the light-harvesting complex since (a) phosphatidylcholine vesicles themselves did not undergo cation-induced aggregation, and (b) mild trypsin digestion of the surface-exposed regions of the light-harvesting complex blocked cation-induced lamellar appression. The particles in the appressed vesicle membranes tended to form long, linear arrays of particles, with occasional mixed quasi-crystalline arrays with an angular displacement near 72°. Surface-mediated interactions among light-harvesting complex subunits of different membranes are, therefore, related to changes in structural organization and interaction of the particles within the lipid phase of the membrane.Numerous previous studies have implicated the involvement of the light-harvesting complex in mediating grana stocking in intact chloroplast membranes. The data presented herein provide a simulation of the membrane appression phenomena using a single class of chloroplast-derived membrane subunits. The data demonstrate that specific surface-localized regions of the light-harvesting complex are involved in membrane-membrane interactions.     

Examination of host-taxon,environment, and distance effects on leaf fungal endophytes in the dominant woody genus,Metrosideros, on Oʻahu

Fungal endophyte (FE) communities can be shaped by environmental conditions and/or host-plant affinities. Hawaiʻi's landscape-dominant woody genus Metrosideros (Myrtaceae) comprises several vegetatively distinct taxa that are non-randomly distributed across environments, and their FE communities are poorly known. We examined the relative importance of Metrosideros taxon and environment (elevation) on FE communities on Oʻahu. ITS1 rDNA barcoding and sequencing of 113 trees detected a richness of 1,637 FEs representing 5 phyla, 223 genera, and 200 species. Variation in FE diversity was significantly explained by host taxon and site with considerable overlap in FE communities among taxa. FE communities did not vary between pubescent and glabrous taxa or across elevations, possibly due to the relatively narrow range of environmental conditions represented on Oʻahu relative to taller islands. A significant pattern of isolation by distance in FE composition was detected both among and within sites, consistent with restricted dispersal of FEs across the island.     

胭脂红景天引种至西藏日喀则其渗透调节物质及保护酶活性的变化

胭脂红景天叶片呈胭脂红色,花开红色,具有极强的耐寒性和耐旱性,是优良的城市绿化植物。为了扩大胭脂红景天的应用范围,丰富恶劣生境的绿化材料,本试验对从哈尔滨引种到西藏日喀则表现良好的胭脂红景天进行了生理适应性研究。结果表明,随着栽植时间的延长,胭脂红景天叶片中丙二醛含量逐渐升高,但增加的幅度较小,脯氨酸含量先降低后升高,SOD、POD、CAT等保护酶的活性均呈先升高后降低的趋势。胭脂红景天可以通过增加体内渗透调节物质含量和提高保护酶活性来调节自身的生理代谢,适应日喀则地区高辐射、干旱等条件。     

Behavioural crypsis in a South African galaxiid fish induced by predatory and non-predatory heterospecifics

This study investigated recognition of, and behavioural responses to, predatory and non-predatory heterospecifics by a small cryptically coloured fish species, Galaxias ‘nebula’. Nebula recognised and differentiated between predatory and non-predatory heterospecifics and altered its behaviour facultatively. With both predatory and non-predatory fishes, the proportion of time spent motionless increased, whereas refugia use was affected only by predators and neither heterospecific affected the time spent active. Although nebula appeared to face no conflict, in that their responses to predatory and non-predatory heterospecifics varied in the same direction and differed only in intensity, the presence of both heterospecifics together induced responses midway between those for each heterospecific separately. Non-predatory heterospecifics thus modified nebula's responses towards predators, potentially making time available for other essential activities such as foraging. This modified predator response may aid its survival in an increasingly threatened habitat.     

Study of PE and iPP orientations on the surface of carbon nanotubes by using molecular dynamic simulations

In this study, the early stage of interfacial crystallisation behaviour of low molecular weight polyethylene (PE) and isotactic polypropylene (iPP) oligomer on the surface of carbon nanotubes (CNTs) with different diameters, chiralities and topography structures was studied using MD simulations. We started to simulate the effect of CNTs chirality and diameter on PE molecular chain orientation, and then the effect of CNTs topography structure on PE and iPP molecular chain orientation was investigated. Finally, some experiments were carried out to prove the simulated results. Our study shows that for CNTs with a diameter comparable with the radius of gyration (R_g) of a polymer chain, an easy orientation of PE chains along CNTs axis is observed for all the systems of the CNTs with different chiralities due to a geometric confinement effect. For CNTs with a much larger diameter, multiple orientation of PE chains is induced on its surface due to the lattice matching between graphite lattice and PE molecular chains. In this case, the chirality of CNTs dominates the orientation of graphite lattice, which determines the orientation of PE chains arrangement on CNTs surface. More importantly, it was found that the groove structure formed by CNT bundles is very useful for the stabilisation of polymer chain, and thus facilitates the orientation of molecular chain along the long axis of CNTs. As a result, a novel nanohybrid shish–kebab (NHSK) structure with CNTs acting as central shish while polymer lamellae as kebab can be successfully obtained for both PE with zigzag conformation and iPP with helical conformation. This simulation result was well supported by the experimental observation. Our study could provide not only a deep understanding of the origin of the polymer chain orientation on CNTs surface but also the guidance for the preparation of polymer/CNTs nanocomposites with novel NHSK structure.     

METAMORPHOSIS OF THE LARVA OF THE POLYCHAETE ARENICOLA CRISTATA. MORPHOLOGY OF THE ‘HOUR-GLASS’ STAGE

The constricted ‘waist’ of the metamorphosing larva of the polychaete Arenicola cristata is described, using light and electron microscopy. The constriction is shown to be the consequence of the discharge and collapse of a post-trochal ring of epithelial cells which remain as functional components of the post-metamorphic juvenile. Morphological differentiation of neuro-effector and interneuronal contacts is initiated at this time. Muscular and neural changes are discussed in terms of their role in effecting metamorphosis.     

The ‘other side’ of embedded ness: A case‐study of the interplay of economy and ethnicity

As interest in ethnics and their entrepreneurial activities has grown in recent years, sociologists have come to emphasize the importance of ethnic social structures as the source of actions propelling business growth. In a sign of convergence with the ‘new economic sociology’, recent literature suggests that embeddedness in ethnic networks and communities leads to cooperative, if not conformist, behaviour among ethnic economic actors. This article looks at the ‘other side’ of embeddedness, through a case‐study of African‐American, Caribbean, Korean and white construction contractors in New York City. I argue that, in construction, the embeddedness of economic behaviour in ongoing social relations among a myriad of social actors impedes access to outsiders. Embeddedness contributes to the liabilities of newness that all neophytes encounter, breeding a preference for established players with track records. However, the convergence of economic and ethnic ties has a further baneful effect, since outsiders also fall outside those networks that define the industrial community. While African‐American, Caribbean and Korean outsiders all experience these barriers in similar ways, they differ in the adaptive strategies that they have pursued. African Americans appear to be most disadvantaged, in part because they have been the most exposed to the social closure that results from the mobilization of white ethnics’ social capital. By contrast, Caribbeans and Koreans entered the labour market in societies where racial domination played little or no role in labour market outcomes ‐ a considerable asset since construction skills are transferable from one society to another. The Koreans appear to be the most embedded in ethnic networks, through which they secure jobs and skilled labour, though class factors play a role here as well and even the Koreans must reach out beyond the ethnic community for a clientele. By contrast, ethnic solidarity operates less powerfully among the black contractors, who are tied to a community where intra‐ethnic diversity and internal competition have grown as a result of immigration. In the absence of an ethnic market, black'entrepreneurs turn to the state, whose requirements and dependence on union labour expose black builders to risks from which their Korean counterparts are sheltered.