Evidence for a functional membrane barrier in the transition zone between the flagellum and cell body of Chlamydomonas eugametos gametes

Evidence is presented which supports the concept of a functional membrane barrier in the transition zone at the base of each flagellum of Chlamydomonas eugametos gametes. This makes it unlikely that agglutination factors present on the surface of the cell body can diffuse or be transported to the flagellar membrane. The evidence is as follows: 1) The glycoprotein composition of the flagellar membrane is very different to that of the cell-body plasma membrane. 2) The flagella of gametes treated with cycloheximide, tunicamycin or , -dipyridyl become non-agglutinable but the source of agglutination factors on the cell body is not affected. 3) Even under natural conditions when the flagella are non-agglutinable, for example in vis-à-vis pairs or in appropriate cell strains that are non-agglutinable in the dark, the cell bodies maintain the normal complement of active agglutinins. 4) When flagella of living cells are labeled with antibodies bound to fluorescein, the label does not diffuse onto the cell-body surface. 5) When gametes fuse to form vis-à-vis pairs, the original mating-type-specific antigenicity of each cell body is slowly lost (probably due to the antigens diffusing over both cell bodies), while the specific antigenicity of the flagellar surface is maintained. Even when the flagella of vis-à-vis pairs are regenerated from cell bodies with mixed antigenicity, the antigenicity of the flagella remains matingtype-specific. 6) Evidence is presented for the existence of a pool of agglutination factors within the cell bodies but not on the outer surface of the cells.Abbreviations and symbols CHI cycloheximide - GTC guaniline thiocyanate - mt ⁺/mt ^- mating type plus or minus - PAS Periodic-acid-Schiff reagent - SDS sodium dodecyl sulphate     

Modulating effects of naturally occurring indoles on SCE induction depend largely on the type of mutagen

The modulating effects of pretreatment of cultured cells with indole-3-carbinol (I3C) and indole-3-acetonitrile (I3A) on the induction of sister-chromatid exchanges (SCEs) by mutagens from different chemical classes were investigated. Cultured primary chick embryo hepatocytes were treated for different periods with I3C (25 micrograms/ml) and with I3A (35 micrograms/ml). Treatment with I3C resulted in a 3-fold increase in ethoxyresorufine-O-deethylase (Erod) activity and a 2-fold increase in ethoxycoumarine-O-deethylase (Etco) activity. Treatment with I3A resulted in a 1.6-fold increase in Erod activity and a 2-fold increase in Etco activity. Pretreatment of cultured primary chick embryo hepatocytes with I3C resulted in a 30-45% decrease in the number of SCEs induced by benzo[a]pyrene (B(a)P) and dimethylnitrosamine (DMN) in co-cultured V79 Chinese hamster cells. No decrease in SCE induction was observed for 2-aminoanthracene (2AA) and the direct-acting alkylating agent ethyl methanesulphonate (EMS). In contrast, when dibromoethane (DBE) was tested pretreatment with I3C resulted in an increase in SCE induction. Pretreatment with I3A again resulted in a 20-40% decrease in SCE induction for B(a)P whereas no decrease was observed for DMN, 2AA and EMS. The results of this study indicate that the type of effect of indole pretreatment largely depends on the type of mutagen selected.     

A fluorescence quenching technique for the measurement of paramagnetic ion concentrations at the membrane/water interface. Intrinsic and X537A-mediated cobalt fluxes across lipid bilayer membranes

We have characterized the quenching of N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)phosphatidylethanolamine by Co2+ in egg phosphatidylcholine (PC) lipid bilayer vesicles. The quenching constant obtained is 59 M-1. We demonstrate one use of this fluorescence quenching technique by measuring intrinsic and X537A-mediated transmembrane Co2+ fluxes in large unilamellar PC vesicles. The intrinsic rate constant for Co2+ flux we measure is 3 X 10(-6) S-1. We confirm that the neutral Co approximately (X537A)2 complex is the main component of the X537A-mediated cobalt flux. Since this method measures the concentration of Co2+ at the site of the fluorophore, it is generally applicable to the measurement of paramagnetic ion concentrations in the region of the membrane/water interface.     

Processing of a chimeric protein in chloroplasts is different in transgenic maize and tobacco plants

Transgenic maize (Zea mays L.) and tobacco (Nicotiana tabacum Petit Havana SR1) plants have been generated, which overproduce a mitochondrial Nicotiana plumbaginifolia manganese superoxide dismutase (MnSOD) in chloroplasts. For this, the mature MnSOD-coding sequence was fused to a chloroplast transit peptide from a Pisum sativum ribulose-1,5-bisphosphate carboxylase (Rubisco) gene and expression of the chimeric gene was driven by the cauliflower mosaic virus (CaMV) 35S promoter. The transgenic MnSOD gene product was correctly targeted to the chloroplasts both in maize and tobacco. However, despite the use of the CaMV 35S promoter, the MnSOD was predominantly localized in the chloroplasts of the bundle sheath cells of maize. Furthermore, the transit peptide was cleaved off at a different position in maize and tobacco.     

A radiometric technique for measuring nicotinamide adenine dinucleotide in femtomole quantities: methodology and application.

A radiometric technique for measuring as little as 1 × 10^?13 moles (100 femtomoles) of nicotinamide adenine dinucleotide (NAD) is presented. Alcohol dehydrogenase (ADH) (EC 1.1.1.1) is used to oxidize 1-[³H]-ethanol to acetaldehyde in the presence of NAD. The [³H]-NAD so produced is used to reduce pyruvate to [³H]-lactate in the presence of lactic acid dehydrogenase (LDH) (EC 1.1.1.27). In this manner, [³H]-lactate is generated, and NAD is regenerated, permitting the reactions to cycle.After a suitable incubation period, unreacted 1-[³H]-ethanol and acetaldehyde in the reaction mixture are evaporated. Nonvolatile [³H]-lactate is quantitated in a scintillation spectrometer. The applicability of the technique to the measurement of NAD in isolated islets of Langerhans is presented.     

Indomethacin reversal of ethanol-induced suppression of ovine fetal breathing movements and relationship to prostaglandin E2

The effects of indomethacin on the ethanol-induced suppression of fetal breathing movements and fetal arterial plasma and cerebrospinal fluid (CSF) PGE2 concentrations and maternal arterial plasma PGE2 concentration were determined in the near-term fetal lamb. Eight conscious instrumented pregnant ewes (between 130 and 133 days of gestation; term, 147 days) received 1-h maternal intravenous infusion of 1 g ethanol/kg total body weight, and the fetus received 6-h intravenous infusion of indomethacin (1 mg/h per kg fetal body weight) commencing 30 min later. Serial fetal and maternal arterial blood samples (n = 8) and fetal CSF samples (n = 5) were collected at selected times throughout the 12-h study for the determination of PGE2 concentration. Fetal breathing movements were monitored continuously throughout the experimental period. Maternal ethanol infusion resulted in initial suppression (P less than 0.05) of fetal breathing movements for 2 h below pretreatment value, followed by a rapid increase in the incidence of fetal breathing movements after the onset of fetal indomethacin treatment. Fetal and maternal plasma PGE2 concentrations and fetal CSF PGE2 concentration were increased (P less than 0.05) above the pre-infusion value during the administration of ethanol and 1 h thereafter. Fetal indomethacin treatment suppressed (P less than 0.05) to undetectable levels fetal plasma and CSF PGE2 concentrations, which then became similar (P greater than 0.05) to pretreatment by 12 h. There was a positive correlation between fetal plasma and CSF PGE2 concentrations. There was an inverse correlation between the incidence of fetal breathing movements and fetal CSF PGE2 concentration.(ABSTRACT TRUNCATED AT 250 WORDS)     

Review: Helicobacter pylori in pediatrics

Despite a decrease in the prevalence of Helicobacter pylori infection, it still poses a significant health burden worldwide. This review summarizes important pediatric studies on H pylori published from April 2018 to March 2019. Epidemiologic studies have reported different prevalences in different parts of the world and have mainly confirmed traditional risk factors. Several studies on pathophysiology attempted to identify risk markers in childhood for gastric cancer development later in life. One of the most interesting studies evaluated the relationship between eosinophilic esophagitis and H pylori infection; however, an inverse relationship was not confirmed. The high resistance of H pylori and, consequently, low eradication rates, is still a major concern and susceptibility testing before treatment has again been highlighted. Potassium‐competitive acid blockers are promising new acid‐suppressant drugs but their role in H pylori eradication schemes is still to be determined.