Regional assignment of five genes on human chromosome 19

A human-mouse hybrid segregant HM76Dd40-6 with new characteristics was derived from the hybrid cell line HM76Dd containing human chromosome 19 as the only human chromosome. Three virus sensitivities located on human chromosome 19 (PVS, E11S and RDRC) were lost in HM76Dd40-6, while six other genes (C3, LDLR, EF2, GPI, PEPD and MANB) were retained. Cytogenetic analysis and in situ hybridization using human or mouse repeated sequences as probes showed that the region q13.1-qter of human chromosome 19 had been replaced by a fragment of mouse chromosome. Our results permit further regional assignment for the following five genes on human chromosome 19: GPI in the region cen-q12, MANB in p13.2-q12, E11S and RDRC in q13.1-qter, and EF2 in pter-q12.     

Two affinity states of M1 muscarine receptors

1. The binding of oxotremorine-M to M1 muscarine receptors was examined by measuring competition between the agonist and 3H-pirenzepine, using rabbit hippocampal membranes suspended in 20 mM Tris buffer containing 1 mM Mn2+. 2. Both ligands interacted with a single class of receptors. The receptors could assume two affinity states for oxotremorine-M, with equal numbers of high-affinity (KH) and low-affinity (KL) sites. 3. KH interconverted reversibly to KL in the absence of divalent cations and interconverted reversibly to a state similar to KL in the presence of guanyl 5'-yl imidodiphosphate. 4. The results are compatible with a model in which a pair of receptor molecules can be stabilized by a guanine nucleotide-binding "G protein" and have one site each of KH and KL affinity.     

Correlation Between Degradation of Bacteriophage T2 Deoxyribonucleic Acid and the Resistance of Escherichia coli to Infection

The ability of certain strains of Escherichia coli to degrade T2 deoxyribonucleic acid to acid-soluble fragments is correlated with their high capacity to survive T2 infection.     

Actions of Excitatory Amino Acids on Somatostatin Release from Cortical Neurons in Primary Cultures

L-Glutamate, N-methyl-D-aspartic acid (NMDA), quisqualate, and kainate were found to increase endogenous somatostatin release from primary cultures of rat cortical neurons in a dose-dependent manner. The rank order of potency calculated from the dose-response curves was quisqualate greater than glutamate = NMDA greater than kainate, with EC50 values of 0.4, 20, and 40 microM, respectively. Alanine, glutamine, and glycine did not modify the release of somatostatin. The stimulation of somatostatin release elicited by L-glutamate was Ca2+ dependent, was decreased by Mg2+, and was blocked by DL-amino-5-phosphonovaleric acid (APV) and thienylphencyclidine (TCP), two specific antagonists of NMDA receptors. The NMDA stimulatory effect was strongly inhibited by APV in a competitive manner (IC50 = 50 microM) and by TCP in a noncompetitive manner (IC50 = 90 nM). The release of somatostatin induced by the excitatory amino acid agonists was not blocked by tetrodotoxin (1 microM), a result suggesting that tetrodotoxin-sensitive, sodium-dependent action potentials are not involved in the effect. Somatostatin release in response to NMDA was potentiated by glycine, but the inhibitory strychnine-sensitive glycine receptor did not appear to be involved. Our data suggest that glutamate exerts its stimulatory action on somatostatin release essentially through an NMDA receptor subtype.     

Fatty acid composition as a taxonomic characteristic for Microcystis and other coccoid cyanobacteria (blue-green alga) isolates

The taxonomic importance of fatty acid composition at genus and sub-genus level was evaluated by analysing the fatty acid composition of fourteen different Microcystis isolates and seven additional members of the order Chroococcales. Fatty acid composition proved to be consistent within isolates. Isolates were clustered into two major groups, namely A and B. Group B contained all the Microcystis isolates and was further divided into subgroups of varying similarity indicating the existence of different taxa. The Microcystis isolates were characterised by a high content of polyunsaturated fatty acids (27–44%) and a low content of palmitoleate. The test organisms were arranged in a scheme indicating their possible phylogenetic relationship based on fatty acid composition and other phenotypic characteristics. According to our data the toxic strains, represented by different isolates, of Microcystis appear as a distinct group. Furthermore two dubious species namely Microcystis incerta and a Synechocystis sp. could clearly be reasigned to different genera. The results demonstrated that fatty acid composition is an effective taxonomic tool in clarifying taxonomical problems of Microcystis isolates. Department of Microbiology, University of the Orange Free State     

Factors involved in capillary growth in the heart

Growth of capillaries in the heart occurs under physiological circumstances during endurance exercise training, exposure to high altitude and/or cold, and changes in cardiac metabolism or heart rate elicited by modification of thyroid hormone levels. Capillary growth in all these conditions can be linked with increased coronary blood flow, decreased heart rate, or both. This paper brings evidence that, although increased blood flow due to long-term administration of coronary vasodilators results in capillary growth, a long-term decrease in heart rate induced by electrical bradycardial pacing in rabbits and pigs, or by chronic administration of a bradycardic drug, alinidine, in rats, stimulates capillary growth with little or no change in coronary blood flow. Decreased heart rate results in increased capillary wall tension, increased end-diastolic volume and increased force of contraction, and thus stretch of the capillary wall. This could lead to release of various growth factors possibly stored in the capillary basement membrane. Correlation was found between capillary density (CD) and the levels of low molecular endothelial cell stimulating angiogenic factor (ESAF) both in rabbit and pig hearts with CD increased by pacing. There was no relation between expression of mRNA for basic fibroblast growth factor and CD in sham-operated and paced rabbit hearts. In contrast, mRNA for TGFß was increased in paced hearts, and the possible role of this factor in the regulation of capillary growth induced by bradycardia is discussed.     

Renal sodium-d-glucose cotransport system. Involvement of tyrosine residues in sodium-transporter interaction

Using brush-border membrane vesicles isolated from calf kidney cortex the effect of tyrosine-reactive reagents on sodium-dependent d-glucose transport was investigated. Treatment of the membranes for 60 min with NBD-Cl (7-chloro-4-nitrobenzo-2-oxa-1,3-diazole), N-acetylimidazole or tetranitromethane decreased d-glucose uptake 50, 70 and 40%, respectively. Tracer exchange experiments revealed that the inhibition of transport is due to a direct modification of the sodium-d-glucose cotransport system. The modification by NBD-Cl decreases the apparent V_max of the transport system with respect to its interaction with sodium. In addition, the rate of inactivation of the transport system by NBD-Cl is reduced in the presence of high concentrations of sodium. The results indicate that tyrosine residues play an essential role in sodium-d-glucose cotransport and are probably involved in the binding and/or transport of sodium by the sodium-d-glucose cotransport system.     

Tissue- and species-specific expression of cytochrome c oxidase isozymes in vertebrates

Cytochrome c oxidase was isolated from brown fat tissue of the rat and compared with the isozymes from rat liver and heart, which differ at least in subunits VIa and VIII. ELISA titrations of COX from the three tissues with monospecific antisera to all 13 subunits of the rat liver enzyme showed differences between the three enzymes. The N-terminal amino-acid sequence analysis of subunits VIa and VIII from SDS-PAGE gel bands of the three enzymes indicates the occurrence of three different isozymes in the rat. N-terminal amino-acid sequence analysis of subunits VIa and VIII from cytochrome c oxidase of bovine and human heart demonstrates also species-specific differences in the expression of the 'liver-type' and 'heart-type' of subunits VIa and VIII.     

Biological properties of human melanoma cells in culture

Summary Three human melanoma cell lines derived from one primary and two metastatic tumors from three different patients were characterized for growth properties usually associated with malignant transformation; these include cell morphology, growth rate, saturation density, growth in semisolid media, colony-forming ability on contact-inhibited monolayers of normal fibroblasts and epithelial cells, and tumorigenicity in immunosuppressed mice. Variations in expression of aberrant properties were evident among the lines. One of the metastatic lines satisfied all the parameters of malignancy tested and the other showed a number of these properties, whereas the primary essentially fulfilled only one. These results suggest that cultured melanoma cells reflect the clinical variability often observed among melanoma patients and the metastatic melanoma seems to display a higher degree of malignant transformation than the primary. THis work was supported in part by USPHS Grant No. 5 T01 AI00332-06 from the National Institutes of Health, Contract E73-2001-N01-CP-3-3237 from the Virus Cancer Program of the National Cancer Institute, and USPHS Grant No. 0H00714-02 from the National Institute for Occupational Safety and Health.