Author Correction: 2600-years of stratospheric volcanism through sulfate isotopes.

The authors became aware of a mistake in the data and axis labeling in Fig. 2 in the original version of the Article. Specifically, the authors mistakenly copied and pasted a formula for background correction instead of the actual values.

2600-years of stratospheric volcanism through sulfate isotopes.

High quality records of stratospheric volcanic eruptions, required to model past climate variability, have been constructed by identifying synchronous (bipolar) volcanic sulfate horizons in Greenland and Antarctic ice cores. Here we present a new 2600-year chronology of stratospheric volcanic events using an independent approach that relies on isotopic signatures (ΔS and in some cases ΔO) of ice core sulfate from five closely-located ice cores from Dome C, Antarctica. The Dome C stratospheric reconstruction provides independent validation of prior reconstructions.

Laboratory study of nitrate photolysis in Antarctic snow. II. Isotopic effects and wavelength dependence.

Atmospheric nitrate is preserved in Antarctic snow firn and ice. However, at low snow accumulation sites, post-depositional processes induced by sunlight obscure its interpretation. The goal of these studies (see also Paper I by Meusinger et al.

Laboratory study of nitrate photolysis in Antarctic snow. I. Observed quantum yield, domain of photolysis, and secondary chemistry.

Post-depositional processes alter nitrate concentration and nitrate isotopic composition in the top layers of snow at sites with low snow accumulation rates, such as Dome C, Antarctica. Available nitrate ice core records can provide input for studying past atmospheres and climate if such processes are understood. It has been shown that photolysis of nitrate in the snowpack plays a major role in nitrate loss and that the photolysis products have a significant influence on the local troposphere as well as on other species in the snow.

Analysis of oxygen-17 excess of nitrate and sulfate at sub-micromole levels using the pyrolysis method.

Rationale: The oxygen-17 excess (Δ(17)O) of nitrate and sulfate contains valuable information regarding their atmospheric formation pathways. However, the current pyrolysis method to measure Δ(17)O requires large sample amounts (>4 µmol for nitrate and >1 µmol for sulfate). We present a new approach employing a Gas Bench interface which cryofocuses O2 produced from sample pyrolysis, enabling the analysis of sub-micromole size samples.

Isotopic composition of atmospheric nitrate in a tropical marine boundary layer.

Long-term observations of the reactive chemical composition of the tropical marine boundary layer (MBL) are rare, despite its crucial role for the chemical stability of the atmosphere. Recent observations of reactive bromine species in the tropical MBL showed unexpectedly high levels that could potentially have an impact on the ozone budget. Uncertainties in the ozone budget are amplified by our poor understanding of the fate of NOx (= NO + NO2), particularly the importance of nighttime chemical NOx sinks.

Oxygen isotope exchange with quartz during pyrolysis of silver sulfate and silver nitrate.

Rationale: Triple oxygen isotopes of sulfate and nitrate are useful metrics for the chemistry of their formation. Existing measurement methods, however, do not account for oxygen atom exchange with quartz during the thermal decomposition of sulfate. We present evidence for oxygen atom exchange, a simple modification to prevent exchange, and a correction for previous measurements.

Measurement of the 17O-excess (Δ17O) of tropospheric ozone using a nitrite-coated filter.

Rationale: The (17)O-excess (Δ(17)O) of tropospheric ozone (O(3)) serves as a useful marker in studies of atmospheric oxidation pathways; however, due to the complexity and expense of currently available analytical techniques, no systematic sampling campaign has yet been undertaken and natural variations in Δ(17)O(O(3)) are therefore not well constrained.

Methods: The nitrite-coated filter method is a new technique for O(3) isotope analysis that employs the aqueous phase NO(2)(-) + O(3) → NO(3)(-) + O(2) reaction to obtain quantitative information on O(3) via the oxygen atom transfer to nitrate (NO(3)(-)). The triple-oxygen isotope analysis of the NO(3)(-) produced during this reaction, achieved in this study using the bacterial denitrifier method followed by isotope-ratio mass spectrometry (IRMS), directly yields the Δ(17)O value transferred from O(3).

Effect of nicotine on fibroblast beta 1 integrin expression and distribution in vitro.

Background: Integrins are a family of transmembrane cell surface glycoproteins, and those with the beta 1-subunit function in both cell-to-cell and cell-to-substrate adhesion. The purpose of this study was to determine nicotine's effect on the expression and distribution of the beta 1 integrin subunit on the human gingival fibroblast cell surface.

Methods: Pure nicotine was diluted in medium to the following concentrations: 0 (control), 0.

Exocellular phospholipase C activity from a Propionibacterium acnes strain isolated from a periodontal pocket.

The culture supernatant of a strain of Propionibacterium acnes was investigated for its phospholipase (PL) activity. The microorganism was isolated from a periodontal pocket of a patient with periodontal disease. Supernatants from cultures of this microorganism were used as a source to obtain enzymes.

Effects of an aminomethacrylate on epithelial cell lipid metabolism.

Methacrylates can affect cell functions by surfactant-like effects or by altering cell lipid composition. Dimethylaminoethyl methacrylate (DMAEMA), an activator widely used in visible-light polymerized dental resins has been shown to elute readily into aqueous environments. The current study examined the metabolism of this material by oral epithelial cells (HCP) and its subsequent effects on cell lipids.

Binding and uptake of N-nitrosonornicotine by oral epithelial cells.

N-nitrosonornicotine (NNN), a significant nitrosamine component of tobacco binds to and is taken up by cells prior to its activation by intracellular enzymes. A variety of factors may affect the binding of substances to a cell including the cell type, medium composition and the cell membrane lipid composition. This study examines the binding and uptake of NNN to various cell types and relates these to the cells' lipid composition.

In vivo effects of Sn-1,2-dioctanoylglycerol, TPA and A23187 on hamster cheek pouch epithelium.

Cheek pouches of male Syrian golden hamsters were topically treated with a single dose of TPA (.5 microgram), calcium ionophore A23187 (75 micrograms) or Sn-1,2-dioctanoylglycerol (DiC8) (500 micrograms) dissolved in 0.25 ml acetone.

Phorbol ester binding to oral epithelial cells in the presence of retinoic acid or N-nitrosonornicotine.

Although the specific mechanisms by which phorbol ester tumour promoters exert their various effects are not known, their actions are mediated by cell membrane receptors which contain lipids as major components of the receptor complex. Since cell modulators such as retinoic acid (RA) and nitrosonornicotine (NNN) can alter cell lipids, the binding of a phorbol ester to cells was examined at time intervals when lipid changes mediated by these modulators occur. Epithelial cells prepared from hamster cheek pouches were treated with all-trans RA or NNN for varying periods of time, then specific binding of phorbol esters was investigated.

Oral epithelial cell lipid synthesis in the presence of retinoic acid or nitrosonornicotine.

The current study examines the effects of N-nitrosonornicotine (NNN) and all trans-retinoic acid (RA) on the synthesis and composition of lipids of oral epithelial cells grown in culture. Cells were exposed to NNN, RA or methylene chloride (the vehicle for the NNN and RA) and the lipids labelled with [14C]-acetate. Lipids were extracted from the cells, separated by paper chromatography, located by autoradiography, and acetate incorporation determined by liquid scintillation spectrometry.

A simplified method for culture of oral epithelial cells.

In order to facilitate studies on oral mucosa a simplified method for the culture of oral epithelial cells from adult hamsters was developed. Cheek pouches were excised and epithelial cells isolated by collagenase digestion. These were grown in CM-V medium containing spermine in order to inhibit overgrowth of the epithelial cells by fibroblasts.

The effects of retinoic acid on [14C]acetate incorporation into lipids of normal and transformed hamster fibroblasts.

This study examined the effects of retinoic acid (RA) on [14C]acetate incorporation and fatty acid composition of hamster embryo fibroblasts (HEF) and two cell lines derived from the same inbred strain but transformed by herpes simplex-2 virus (HSV) or polyoma virus (HFT). Cells were exposed to all trans RA, or dimethylsulfoxide (DMSO), the vehicle for RA, and the lipids labeled with [14C]acetate. Lipids were extracted from the cells, separated by paper chromatography, located by autoradiography, and acetate incorporation determined by liquid scintillation spectrometry.

Effects of 12-0-tetradecanoyl-phorbol-13-acetate on oral epithelium in vitro.

TPA, a tumor promotor whose initial site of action is the cell membrane, was examined for its actions on hamster oral mucosa using light and scanning electron-microscopic procedures. Hamster cheek-pouch explants were cultured in vitro, then treated for 72 h with 1.6 X 10(-8) M TPA.

Effects of calcium ions on hamster cheek pouch epithelium grown in vitro.

Epithelial outgrowths from hamster cheek pouch explants were cultured for 14 days in media containing calcium concentrations of 0.05 mM, 0.075 mM, 0.

Phospholipase A activity in supernatants from cultures of Bacteroides melaninogenicus.

The phospholipase A activity in culture supernatants of two strains of Bacteroides melaninogenicus is described. The enzyme utilize phosphatidylcholine as substrate and produce mainly lysophosphatidylcholine and free fatty acids. The activities are Ca2+-independent, are not affected by the presence of a chelating agent, have a broad pH range (5-9) and an optimum temperature for activity of approx.

Effects of retinoic acid on the differentiation of hamster cheek pouch epithelium grown in vitro.

Recently our laboratories have successfully attained preferential epithelial outgrowths from hamster cheek pouch explants. This has allowed us to systematically analyze oral epithelial cell differentiation as weel las examine the modulatory effects of various physiologic and pharmacologic agents in this epithelial cell system. The objective of the current investigation was to study the effects of various doses of retinoic acid (RA) on the epithelial outgrowths of hamster cheek pouch.