A theoretical model for water flux through the artery wall

A two layer model for water flux through the artery is studied using a mathematical model based on the theory for the consolidation of water saturated soils. The matrix is considered to be constituted by two layers with different permeabilities and different elastic constants and the two systems of equations are coupled with the condition of continuity of pressure, total stress, solid displacement and fluid seepage velocity at the interface. The luminal pressure is considered to be harmonic in time. Exact solutions are obtained for displacements and pressures in both the layers. For large consolidation times, large pressure gradients are found to exist near the boundaries and at the interface. The heterogeneous model may not only be useful to understand the mechanics of transport in the physiological system but it will also help the bioengineers to choose proper implant materials to design artificial vascular organs for the purpose of prosthesis.     

Five genetic loci involved in the synthesis of acidic exopolysaccharides are closely linked in the genome of Rhizobium sp strain NGR234

Summary R-prime plasmids were constructed from a derivative of Rhizobium strain NGR234 (ANU280) and were shown to contain overlapping genomic DNA segments involved in biosynthesis of exopolysaccharides (EPS). The R-primes originally constructed carried the mutant allele from Tn5-induced EPS-deficient (Exo^–) mutant ANU2811. This plasmid-located mutant allele was dominant to the corresponding wild-type allele as merodiploid strains were Exo^–. Exo⁺ revertants occurred at a low rate (1×10^-7) and these were shown to result from double reciprocal recombination events, which led to the isolation of R-prime plasmids carrying functional wild-type exo alleles. R-prime plasmids that carry overlapping segments of DNA from parental strain ANU280 complemented 28 of the 30 group 2 Exo^– mutants of strain ANU280. Complementation of these Exo^– mutants also restored their symbiotic abilities of effective nodulation. Subsequent in vivo recombination between the wild-type alleles located on the R-prime and the corresponding mutated allele on the genome, was used to generate a new family of R-primes, which carried mutations in the exo genes. The 30 group 2 Exo^– mutants were classified into 7 distinct genetic groups based upon complementation and physical mapping data. Five of the seven exo loci were gentically linked and located on a 15-kb region of DNA. Mutations at two loci were dominant only when the mutations were R-prime plasmid-located while a mutation at a second locus was cis-dominant to two other exo loci. At least five genes involved in the synthesis of acidic exopolysaccharide synthesis have been identified.     

Molecular cloning,characterization and expression of a nitrofuran reductase gene ofescherichia coli

Mini-mu derivatives carrying plasmid replicons can be used to clone genesin vivo. This method was adopted to generate phasmid clones which were later screened for their ability of restore nitrofurantoin sensitivity of a nitrofuran-resistant host by eliciting nitroreductase activity. One phasmid-derived clone (pAJ101) resulted in considerable increase in nitroreductase activity when introduced into a nitrofurantoin-resistant mutant ofEscherichia coli with reduced nitroreductase activity. Subsequently, a 1.8 kb fragment obtained from pAJ101 by partial digestion with 5au3A, was subcloned into pUC18 to yield pAJ102. The nitroreductase activity attributable to pAJ102 was capable of reducing both nitrofurantoin and nitrofurazone. The polypeptides encoded by pAJ102 were identified by the minicell method. A large, well-defined band corresponding to 37 kDa and a smaller, less-defined band corresponding to 35 kDa were detected. Tnl000 mutagenesis was used to delineate the coding segment of the 1.8 kb insert of pAJ102. A 0.8 kb stretch of DNA was shown to be part of the nitroreductase gene. The gene was mapped at 19 min on theEscherichia coli linkage map.     

Inhibitors of nitrofuran reduction in Escherichia coli: evidence for their existence, partial purification, binding of nitrofurantoin in vitro, and implications for nitrofuran resistance

Nitrofurantoin (NF)-resistant mutants of Escherichia coli were isolated as described previously (18). One of the mutants (SSJ-2) was found to possess NF reductase activity equal to that of its parent (E. coli KL16). Two NF-resistant transductional derivatives, SSJ-2A and SSJ-2B, were isolated using SSJ-2 as the donor. SSJ-2 was found to be a double mutant carrying two mutations, nfnA and nfnB, while SSJ-2A (nfnA) and SSJ-2B (nfnB) carried these mutations individually. Heated extracts from SSJ-2A and SSJ-2B were found to inhibit the reduction of NF by unheated extracts of the NF-sensitive strain E. coli KL16 in vitro. Unheated extracts of these mutants reduced NF poorly relative to E. coli KL16. The poor reduction of NF by unheated extracts of SSJ-2A and SSJ-2B was greatly stimulated by heated extracts of SSJ-2B and SSJ-2A, respectively, and also by heated extracts of E. coli KL16. When heated extracts of SSJ-2A and SSJ-2B were mixed in a particular ratio and added to unheated extracts of E. coli KL16 they lost their inhibitory activity. Two proteins, designated inhibitor A and inhibitor B, have been partially purified from heated extracts of SSJ-2B and SSJ-2A, respectively. Their respective molecular weights, as determined by gel chromatography, were 37,000 and 20,500. The two inhibitors bound nitrofurantoin in vitro, and the NF-binding ability was lost when mixed in the molar ration of 3/1 (B/A). These observations were rationalized in terms of a hypothesis which explains (i) maximal NF reduction in wild-type cells, (ii) maximal NF reduction of nfnA-nfnB- double mutant, and (iii) poor NF reduction in nfnA- or nfnB- single mutants. The possible role of these inhibitors in nitrofurantoin resistance is also discussed.     

Identification of the peptides of the crystals of Bacillus thuringiensis var israelensis involved in the mosquito larvicidal activity

Tryptic digestion of the proteins from the purified crystals of B.thuringiensis var israelensis resulted in the decline of high molecular weight peptides without the loss of mosquito larvicidal activity, measured after immobilization of the digests with DEAE- Sephadex A 50 beads. Amongst the peptides generated (less than 44 kDa), a 21 kDa peptide was immunoreactive to the crystal antiserum. Analysis of the peptides released from spores of the toxic (Cry+) and non-toxic (Cry-) strains has revealed a pattern in which only the 26kDa peptide was missing in the Cry-strain. Sporulation and crystal formation were dissociated by the addition of the antibiotic netropsin, which could also inhibit the crystal assembly, without considerable decrease of the larvicidal activity and retention of the 26kDa peptide. These results implicate the 26kDa peptide in the larvicidal action.     

Monitoring ovulation and implantation in the cynomolgus macaque (Macaca fascicularis) through evaluations of urinary estrone conjugates and progesterone metabolites: a technique for the routine evaluation of reproductive parameters

Investigations were undertaken to determine the applicability of recently reported specific radioimmunoassays for urinary estrone conjugates and progesterone metabolites for monitoring ovarian function in the cynomolgus macaque (Macaca fasciularis) and other macaque species. Mean estrone conjugate measurements appear to accurately reflect the preovulatory estrogen peak in both conceptive (n = 5) and nonconceptive (n = 6) cycles, as well as to indicate early pregnancy through increases which are significantly elevated by Day + 15 (p less than 0.049) post estrone conjugates peak. The mean luteal phase levels of these progesterone metabolites are significantly elevated by Day + 14 (p less than 0.012) in conceptive cycles when compared to the mean values for nonconceptive cycles.     

Enhancement of in vivo cell-mediated immune responses by three distinct cytokines

The ability of recombinant/purified cytokines to augment delayed-type hypersensitivity (DTH) responses was investigated. Suboptimal doses of haptenized SC were treated in vitro with purified or recombinant derived cytokines and tested for their ability to enhance DTH in vivo. With the use of this protocol, it was shown that both human and mouse rIL-6, as well as mouse rTNF-alpha, potentiated DTH in a dose-dependent manner. In accordance with these data, IL-6/TNF-alpha-containing supernatant from long term nonlymphoid cell lines also possessed the ability to augment DTH. By using the same protocol, we have also identified T cell hybridomas that produce DTH-augmenting activity constitutively. The hybridoma-derived factor, termed the T cell enhancing factor (TCEF), was functionally distinguishable from the defined cytokines IL-1 through IL-6, IFN-gamma, and TNF by bioassay. Furthermore, RNA derived from the hybridoma failed to hybridize with cDNA probes specific for IL-1 to IL-6, IFN-gamma, TNF-alpha, and granulocyte-macrophage CSF. Further characterization of the serum-free conditioned media derived from the hybridoma indicated that the TCEF was a soluble acid labile glycoprotein (Mr greater than 30,000). Finally, we investigated the cellular requirements for DTH augmentation by IL-6, TNF-alpha, and TCEF; all are dependent upon the presence of T cells in the immunizing inoculum. We propose that these cytokines play a critical role in the development of DTH responses in vivo.     

Free Radical Formation by Ultrasound in Aqueous Solutions. A Spin Trapping Study

Our recent spin trapping studies of free radical generation by ultrasound in aqueous solutions are reviewed. The very high temperatures and pressures induced by acoustic cavitation in collapsing gas bubbles in aqueous solutions exposed to ultrasound lead to the thermal dissociation of water vapor into H atoms and OH radicals. Their formation has been confirmed by spin trapping. Sonochemical reactions occur in the gas phase (pyrolysis reactions), in the gas-liquid interfacial region, and in the bulk of the solution (radiation-chemistry reactions). The high temperature gradients in the interfacial regions lead to pyrolysis products from non-volatile solutes present at sufficiently high concentrations. The sonochemically generated radicals from carboxylic acids, amino acids, dipeptides. sugars, pyrimidine bases. nucleosides and nucleo-tides were identified by spin trapping with the non-volatile spin trap 3.5-dibromo-2.6-dideuterio-4-nitrosobenzenesulfonate. At low concentrations of the non-volatile solutes. the spin-trapped radicals produced by sonolysis are due to H atom and OH radical reactions. At higher concentrations of these non-volatile solutes, sonolysis leads to the formation of additional radicals due to pyrolysis processes (typically methyl radicals). A preferred localization of non-volatile surfactants (compared to analogous non-surfactant solutes) was demonstrated by the detection of pyrolysis radicals at 500-fold lower concentrations. Pyrolysis radicals were also found in the sonolysis of aqueous solutions containing only certain nitrone spin traps. The more hydrophobic the spin trap, the lower the concentration at which the pyrolysis radicals can be observed. The effect of varying the temperature of collapsing transient cavities in aqueous solutions of different rare gases and of N₂O on radical yields and on cell lysis of mammalian cells was investigated.