Electrophysiological demonstration of Na+/Ca2+ exchange in bovine articular chondrocytes

Altered fluxes of Ca2+ across the chondrocyte membrane have been proposed as one pathway by which mechanical load can modulate cartilage turnover. In many cells, Na+/Ca2+ exchange (NCX) plays a key role in Ca2+ homeostasis, and recent studies have suggested it is operative in articular chondrocytes. In this study, an electrophysiological characterisation of NCX in articular bovine chondrocytes has been performed, using the whole-cell patch clamp technique, and the effects of inhibitors and the transmembrane electrochemical gradients of Na+ and Ca2+ on NCX function have been assessed. A Ni2+-sensitive current (I(NCX)) which exhibited outward rectification, was elicited by a voltage ramp protocol. The current was also attenuated by the NCX inhibitors benzamil and KBR7943, without significant differences between the effect of these two compounds upon outward and inward currents. The Ni2+-sensitive current was modulated by changes in extracellular and pipette Na+ and Ca2+ in a manner characteristic of I(NCX). Measured values for the reversal potential differed significantly from those predicted for an exchanger stoichiometry of 3Na+ : 1Ca2+, implying that accumulation of intracellular Ca2+ (from influx or release from stores) or more than one transport mode is occurring. These results demonstrate the operation of NCX in articular chondrocytes and suggest that changes in its turnover rate, as might occur in response to mechanical load, may modify cell composition and thereby dictate cartilage turnover.     

Intracellular Ca(2+) dynamics and sarcomere length in single ventricular myocytes

The measurements of the sarcomere length in dissociated cardiac ventricular myocytes are discussed using mainly our own experimental data. The striation periodicity of these unloaded cells was found to be that which is to be expected of a myocyte free of the ultrastructural constraints imposed upon it by the normal syncytial matrix of the ventricular wall. The sarcomere length and [Ca(2+)] relationship was consistent as expected from the intact tissue, when it was measured soon after partial rupturing the cell membrane. Miniature fluctuations of individual sarcomere length were demonstrated during rest, which was augmented by the Ca(2+) overload. The [Ca(2+)] could be estimated from the measurements of sarcomere length during the positive staircase of contraction. The usefulness of the optical measurement of sarcomere pattern was indicated.     

Biological and environmental effects on fine-scale seed dispersal of an invasive tree in a secondary subtropical forest

Dispersal abilities of invading species emerge from the interaction between the species and some features of the target community. Ligustrum lucidum is a tree species invading different ecosystems. Major spatial patterns of Ligustrum invasions and their ecological consequences have been analyzed, but no study addressed the dispersal process at a fine scale, assessing the effects of different biological and environmental factors. Ligustrum lucidum is an ornithochoric species. The structure of the environment determines bird movements and thus affects seed dispersal. We used inverse modeling to analyze bird-mediated dispersal of L. lucidum seeds in a secondary Yungas forest and surrounding crop-fields. We assessed the effects of egestion mode (regurgitation and defecation) and tree density (as an environment character) on seed dispersal. Seed dispersal presented different spatial patterns depending on the egestion mode. Tree density was positively associated with the number of regurgitated dispersed seeds and negatively associated with the number of defecated dispersed seeds. In both cases, dispersal distance increased in open areas, but absence of perches inhibited seed arrival. Thus, spread of L. lucidum is facilitated in open areas with some trees; inside the native forest, short distance dispersal facilitates the gradual invasion by this exotic species. Our results suggest that processes like crop abandonment and forest succession, which are active in subtropical montane systems, may facilitate L. lucidum invasion. Our seed dispersal models should be combined with actual distribution maps of L. lucidum to identify areas vulnerable to new invasions.     

Effect of magnesium and iron on the hydration and hydrolysis of guar gum

The effect that magnesium and iron have on the hydration and hydrolysis of guar gum at pH 12 was studied as a function of viscosity. It was found that small concentrations of magnesium do not affect the dissolution ratio of guar but significantly decrease hydrolysis at high temperatures. These results suggest that Mg(OH)(2) forms an adduct with the polysaccharide that prevents thermal hydrolysis of the guar. Viscosity measurements recorded in the presence of iron at pH 12 show that ferric iron inhibits hydration or dissolution of guar and may accelerate chain scission of fully hydrated guar when solutions are heated in an autoclave at 121 degrees C.     

Identification of a QTL decreasing yield in barley linked to Mlo powdery mildew resistance

A molecular marker map, including Mlo mildew resistance, of the spring barley cross Derkado (Mlo-resistant) × B83-12/21/5 (Mlo-susceptible) was scanned for yield QTLs to determine whether the association of Mlo resistance with reduced yield was due to linkage or pleiotropy. Over the mapped portion of the genome of the cross, the QTL with the greatest effect upon yield was located within a 22 cM region between mlo and the simple sequence repeat HVM67 on chromosome 4(4H). The association of Mlo resistance with lower yield was therefore due to a repulsion linkage. Analysis of yield component characters revealed QTL alleles for reduced grain number and earlier heading date in the same region, also associated with Mlo resistance. Genotyping of a range of cultivars and sources of Mlo resistance with the HVM67 simple sequence repeat showed that the Derkado HVM67 allele was rare as it was found only in one other cultivar and four land-races or sources of disease resistance. Grannenlose Zweizeilige, the source, and Salome, the carrier of Mlo resistance in Derkado, have the same HVM67 genotype, although Salome was a mixture of two genotypes. The entire mlo-HVM67 chromosomal segment from Grannenlose Zweizeilige is therefore thought to have been transmitted to Derkado, possibly through joint selection for Mlo resistance and early heading. L92, synonym EP79, was another source of Mlo resistance with the same HVM67 allele as Derkado but recombination must have occurred during the breeding of Atem as it possesses a different HVM67 allele which is present in all the other Mlo sources and cultivars surveyed. Abbreviations: GN, grains per main stem ear; HD, heading date; MSTGW, thousand grain weight derived from GN and MSY; MSY, yield of grain on the main stem; PY, yield of grain from the whole plot; sCIM, simplified compound interval mapping; SIM, simple interval mapping; SPY, single plant yield; S-SAP, sequence-specific amplification polymorphism; TGW, thousand grain weight derived from bulk of plot seed; TN, number of fertile stems per plant.     

Genetic map of the opp (Oligopeptide permease) locus of Salmonella typhimurium.

The uptake of peptides by Salmonella typhimurium is mediated by three apparently independent transport systems. One of these systems, the oligopeptide permease, is encoded by a genetic locus (opp) which has been mapped at 34 min on the S. typhimurium chromosomal map. We accurately mapped the location of opp by cotransduction frequencies and by deletion analysis and show that the gene order for this region of the chromosome is cysB-trp-tonB-opp-galU-tdk. All opp mutants, independently isolated by a variety of means, mapped at this one locus, between tonB and galU. Spontaneous and transposon Tn10-generated deletions were used to construct a fine-structure genetic map of opp. Evidence is presented which indicates that opp covers a 5- to 6-kb segment of DNA and is therefore likely to consist of more than one gene.     

Prostaglandin synthesis by enterocyte microsomes of rabbit small intestine

We studied the prostaglandin (PG) synthetic capacity of microsomes of a relatively pure population of rabbit enterocytes and determined ideal conditions for product synthesis. The epithelial cells were freed from the basement membrane by a combination of calcium chelation and mechanical vibration, and 100,000 X g microsomes were prepared. These microsomes were found to synthesize PG from exogenously added arachidonic acid. The ideal conditions for the reaction were a microsomal protein concentration of 1.0 mg/ml, an arachidonic acid concentration of 33 uM, a reaction mixture pH of 8.0-9.5 and with epinephrine 1.5 mM added as a cofactor. The product yields increased linearly with time up to 30 min. of incubation and were inhibited by 100 uM indomethacin. Under the above ideal conditions enterocyte microsomes yielded the following products expressed as pmole/mg protein/20 min. incubation: PGF2 alpha 98 +/- 7, PGE2 48 +/- 9, PGD2 28 +/- 7, TxB2 40 +/- 5, 6 Keto PGF1 alpha 15 +/- 6.     

中国的炭疽杆菌DNA分型及其地理分布

炭疽广泛分布于中国各地,特别是西部地区,并经常造成人畜疾病,在一项合作研究中,用多位点VNTR分析（MLVA）对从1952-1998年自中国主要地理流行区域分离的病人,病畜和土壤等来源的炭疽杆菌进行了基因分型,MLVA分析结果揭示了21种新的基因型,其等位基因组合在以前世界范围分离物的研究中未曾发现,此外,分离物的分群显示,A3b组是地理上最广泛分布的基因组,说明该组可能是中国的“地方流行株”。而来自古丝绸之路重要贸易中心新疆的大量分离株其基因型特别分散。