Distribution of neurons with high-affinity uptake sites for GABA in the myenteric plexus of the guinea-pig,rat and chicken

The occurrence of neurons possessing high-affinity uptake sites for GABA was studied in the myenteric plexus of the guinea-pig ileum, caecum, and proximal and distal colon, the rat proximal colon, and the chicken gizzard with the use of 3H-GABA and autoradiography. Experiments were carried out on plexuses that had been freshly isolated from the gut wall or on isolated plexuses that had been maintained as explant cultures for 7 to 14 days. Scattered neurons selectively labelled with 3H-GABA were found in the myenteric plexuses from all the areas examined. The results suggest that GABAergic neurons are widely distributed in the enteric nervous system.     

Changes in phosphatidylinositol and phosphatidic acid in stimulated human neutrophils: Relationship to calcium mobilization,aggregation and superoxide radical generation

Human neutrophils aggregate and release mediators of inflammation, such as active oxygen species and lysosomal enzymes, when exposed to the chemoattractant, fMet-Leu-Phe, or the tumor promotor, phorbol myristate acetate. In order to ‘stage’ events which may lead to such neutrophil responses, we determined the temporal relationship between stimulus-induced changes in the endogenous phospholipids phosphatidylinositol (PI) and phosphatidic acid, the mobilization of calcium, and the onset of aggregation and generation of superoxide anion during the initial 2 min of cell activation. Within 5 s after addition of fMet-Leu-Phe (10^?7 M) neutrophils accumulated phosphatidic acid and the levels of PI decreased, as determined by two-dimensional thin-layer chromatography and phosphorus determinations. By 5 s, phosphatidic acid levels rose approximately 3.5-fold and at 15 s the loss of PI exceeded the quantity of phosphatidic acid generated. In response to phorbol myristate acetate (1 μg/ml), however, changes in PI or phosphatidic acid were not observed until after 60 s. Accumulation of phosphatidic acid in fMet-Leu-Phe-stimulated cells was not inhibited by chelation of extracellular calcium. Neutrophils exposed to either fMet-Leu-Phe or phorbol myristate acetate also showed rapid decrements in fluorescence of cell-associated chlorotetracycline (used as an indirect probe of mobilization of intracellular membrane-associated calcium) and took up ⁴⁵Ca²⁺ from the extracellular medium (under 60 s). The results indicate that changes in calcium mobilization, together with the alterations in phospholipid metabolism (under 5 s) anteceded aggregation and the generation of O^?₂ (10–15 s) induced by fMet-Leu-Phe. In contrast, when neutrophils were exposed to phorbol myristate acetate, changes in PI and phosphatidic acid (over 60 s) were observed after the mobilization of calcium (under 5 s) and the onset of O^?₂ generation and aggregation (30–35 s).     

Structure of the human erythrocyte blood group P1 glycosphingolipid.

A glycosphingolipid with blood group P1 activity was extracted from an acetone powder of human erythrocyte stroma with chloroform-methanol. It was purified by chromatography on columns of silicic acid and by preparative thin-layer chromatography of the fully acetylated and deacetylated glycolipid. The purified glycolipid contained galactose, N-acetylglucosamine, and glucose in a molar ratio of 3:1:1. Treatment of the P1 glycolipid with fig alpha-galactosidase released a single galactosyl residue and destroyed the blood group activity, and the alpha-galactosidase product had the same chromatographic mobility as paragloboside. Substitution sites on the neutral sugars of the P1 glycolipid and the alpha-galactosidase product were established by identification of methylated alditol acetates, and substitution on N-acetylglucosamine was determined by identification of methyl glycoside derivatives. The terminal nonreducing disaccharide of the P1 glycolipid is Gal(alpha, 1 leads to 4)Gal. N-Acetylglucosamine was identified as the next sugar in sequence by mass spectrometric analysis of the permethylated P1 glycolipid. On the assumption that the glucose residue is linked to ceramide, we propose the following structure for the P1 glycolipid: Gal(alpha, 1 leads to 4)Gal(beta, 1 leads to 4)Glc-NAc(beta, 1 leads to 4)Glc-Cer.     

Correlation of Ultrastructure in Azotobacter vinelandii with Nitrogen Source for Growth

Azotobacter synthesizes an extensive internal membranous nework when grown with air (N₂), i.e., under conditions when these bacteria fix nitrogen. Very slight quantities of internal membrane, concentrated mainly about the cell periphery, are formed when Azotobacter grows with fixed nitrogen, i.e., ammonia and amino acids. Compared to cells growing with ammonia, cells utilizing atmospheric nitrogen as the sole nitrogen source are smaller in size and volume, grow one-third slower, and lack detectable poly-β-hydroxybutyrate.     

Purification of Avian Myeloblastosis Virus DNA Polymerase by Affinity Chromatography on Polycytidylate-Agarose

Polycytidylic acid [poly(rC)] covalently linked to cyanogen bromide-activated agarose is an effective affinity matrix for the RNA-dependent DNA polymerase from avian myeloblastosis virus. Poly(rC)-agarose is capable of binding large quantities of avian myeloblastosis DNA polymerase, which is then eluted by using a linear KCl gradient of increasing concentration. The DNA polymerase isolated from crude, detergent-disrupted virions by a single pass through columns of poly(rC)-agarose appears nearly homogeneous (approximately 90% pure) as determined by sodium dodecyl sulfate-polyacrylamide disc gel electrophoresis. Complete recovery of input enzymatic activity was obtained. Results suggest that polyribonucleotide columns may provide a high-yield, rapid method for the purification of oncornaviral DNA polymerase.     

Lipid composition of subcellular particles of human blood platelets

Human platelets can be fractionated into three main subcellular components: granules, membranes, and a soluble fraction. In this study we determined the phospholipid and neutral lipid content of the granules and membranes. Quantitative relationships between lipids and protein were examined. The fatty acid and aldehyde composition of individual phospholipids and neutral lipids was also determined. Whole platelets had a lower lipid to protein ratio than did the subcellular particles, but the basic lipid composition of the granules, membranes, and platelets was similar. The phospholipid composition of platelets and subcellular fractions was found to differ only in that granules had a lower percentage of lecithin. Each of the phospholipid classes displayed a distinctive fatty acid pattern which was the same in all fractions and in whole platelets. The major neutral lipid was free cholesterol. Cholesteryl esters, triglycerides, and free fatty acids were minor components. The molar ratio of cholesterol to phospholipid in the platelet membranes was lower than that of brain myelin and erythrocyte ghosts. Some differences in fatty acid composition of the neutral lipids of platelet fractions were found. A special lipid composition or constituent that would correlate with platelet function has not been found.     

Selection, Generalized Transmission and the Evolution of Modifier Genes. I. the Reduction Principle

Modifier gene models are used to explore the evolution of features of organisms, such as the genetic system, that are not directly involved in the determination of fitness. Recent work has shown that a general "reduction principle" holds in models of selectively neutral modifiers of recombination, mutation, and migration. Here we present a framework for models of modifier genes that shows these reduction results to be part of a more general theory, for which recombination and mutation are special cases. The deterministic forces that affect the genetic composition of a population can be partitioned into two categories: selection and transmission. Selection includes differential viabilities, fertilities, and mating success. Imperfect transmission occurs as a result of such phenomena as recombination, mutation and migration, meiosis, gene conversion, and meiotic drive. Selectively neutral modifier genes affect transmission, and a neutral modifier gene can evolve only by generating association with selected genes whose transmission it affects. We show that, in randomly mating populations at equilibrium, imperfect transmission of selected genes allows a variance in their marginal fitnesses to be maintained. This variance in the marginal fitnesses of selected genes is what drives the evolution of neutral modifier genes. Populations with a variance in marginal fitnesses at equilibrium are always subject to invasion by modifier genes that bring about perfect transmission of the selected genes. It is also found, within certain constraints, that for modifier genes producing what we call "linear variation" in the transmission processes, a new modifier allele can invade a population at equilibrium if it reduces the level of imperfect transmission acting on the selected genes, and will be expelled if it increases the level of imperfect transmission. Moreover, the strength of the induced selection on the modifier gene is shown to range up to the order of the departure of the genetic system from perfect transmission.