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While the ocean's large-scale overturning circulation is thought to have been significantly different under the climatic conditions of the Last Glacial Maximum (LGM), the exact nature of the glacial circulation and its implications for global carbon cycling continue to be debated. Here we use a global array of ocean-atmosphere radiocarbon disequilibrium estimates to demonstrate a ∼689±53 14C-yr increase in the average residence time of carbon in the deep ocean at the LGM. A predominantly southern-sourced abyssal overturning limb that was more isolated from its shallower northern counterparts is interpreted to have extended from the Southern Ocean, producing a widespread radiocarbon age maximum at mid-depths and depriving the deep ocean of a fast escape route for accumulating respired carbon. While the exact magnitude of the resulting carbon cycle impacts remains to be confirmed, the radiocarbon data suggest an increase in the efficiency of the biological carbon pump that could have accounted for as much as half of the glacial-interglacial CO2 change.

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We have cloned a novel member of the tandem pore K+ channel family from human brain cDNA. The novel cDNA encodes a 330-residue polypeptide of predicted molecular mass 36 kDa. We have named the channel TASK-5 owing to its sequence homology with TASK-1 and TASK-3. TASK-5 mRNA is expressed in pancreas, liver, kidney, lung, ovary, testis and heart. However, expression of TASK-5 in heterologous systems failed to elicit ionic currents. Removal of a putative endoplasmic reticulum retention sequence did not alter this finding and the distribution of channel proteins in HEK293 cells was similar for both TASK-1 and TASK-5. We tested whether TASK-5 could form heteromers with TASK-1. We show a mutant form of TASK-1 (H98N) to have a radically reduced sensitivity to acidification. Proton sensitivity could be rescued by injecting equimolar amounts of wild-type and mutant TASK-1 cRNA into Xenopus oocytes; the effect was that expected if half the channels formed are heteromers. Co-expression of TASK-5 with TASK-1 H98N does not affect the proton sensitivity of mutant TASK-1; thus TASK-5 appears not to form heteromers with TASK-1. Nonetheless, TASK-5 may require some other, unidentified partner subunit to form functional channels in the plasma membrane or it may form a channel in an intracellular organelle.

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The biodegradability of bisphenol A (BPA) was assessed in surface waters from seven different rivers across the United States and Europe. Rapid biodegradation of BPA was observed in all rivers following lag phases ranging from 2 to 4 d. Biodegradation half-lives for BPA were typically less than 2 d following the lag phase. Mineralization of BPA was observed in all river waters, with average carbon dioxide yields of approximately 76% of the theoretical maximum (range 59-103%) at the end of the incubation period (< or = 18 d). Short half-lives (0.5 to 3 d) were noted for BPA biodegradation in river waters regardless of geographic location, sampling site (i.e., upstream vs downstream of wastewater outfalls), sediment addition (< or = 0.05%), and initial test chemical concentration (50-5,500 microgram/L). Subsequent studies conducted at environmentally relevant concentrations (0.05 and 0.5 microgram/L) also indicated short half-lives (3-6 d) for BPA and support the extrapolation of the half-lives measured in this study over a wide range of environmental concentrations. The fact that BPA was degraded rapidly in surface waters taken from diverse locations in the United States and Europe as well as in studies recently conducted in Japan suggests that BPA degrading microorganisms are widely distributed in nature. These observations provide clear evidence that BPA is not persistent in the aquatic environment.

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A channel was identified in cell-attached recordings in rat hippocampal neurones maintained in culture. This channel, which was highly active at the resting membrane potential, was present in most (73 %) patches studied. The channel was characterized by long duration openings and a high open probability (Po, mean value 0.73 at -70 mV) at negative patch potentials with mild voltage dependence over the range -40 to -120 mV. It showed inward rectification. There were up to five active channels in cell-attached recordings in experiments where the cells were bathed in sodium-containing Locke solution. The single channel conductances in cell-attached recordings with 140 or 40 mM K+ in the patch pipette were 26 and 12 pS, respectively. The channel was therefore selective for K+ over Na+. The channel was not permeable to Rb+ ions. The single channel conductance was 24 pS in excised inside-out patches bathed in symmetrical K+ (140 mM) solutions. Examination of the channel kinetics revealed that both the open and closed time distributions could be fitted by the sum of three exponentials, there being no pronounced voltage sensitivity between -60 and -120 mV. The 26 pS K+ channel was insensitive to extracellular TEA, apamin, 4-AP and dequalinium. Neither was it sensitive to intracellular Ca2+. Extracellular Ba2+ was effective in reversibly blocking the channel, the IC50 being 2.0 mM. There was no obvious effect of bath application of the K+ channel opener, lemakalim, or a cAMP analogue. This channel appears to contribute a significant proportion (at least 30 %) of the resting conductance in these neurones.

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We have conducted single-channel patch-clamp experiments in skin fibroblasts maintained in culture. Two different cell lines, a mouse 3T3-L1 cell line and a human B17 cell line, were selected for these pilot studies. Recordings were made from both cell-attached and excised inside-out patches at room temperature. In the case of the 3T3-L1 cells, the success rate in obtaining good seals (> 1Gomega) was low, and channel openings in either cell-attached or excised patches were rare. We have, however, identified a channel in a cell-attached configuration with a slope conductance of 39 pS in symmetrical K+ solutions. In the case of the human B17 cells, good quality seals were more readily obtained. One principal type of channel opening was identified. In cell-attached patches, the prevalent type of channel in symmetrical K+ solutions had a conductance of 187 pS. This channel was activated by strong depolarization, and there was usually more than one active channel in the patch. It was blocked by extracellular tetraethylammonium (20 mM), and persisted when external Cl- was replaced by aspartate. In excised inside-out patches bathed in symmetrical K+, this channel was activated by an increase in Ca+ applied to the intracellular face. A large conductance channel (175 pS) was also observed in excised inside-out patches, with a reverse physiological K+ gradient. This channel had a reversal potential > 40 mV and appeared not to be voltage-dependent under these recording conditions (2 mM Ca(2+)i). We conclude that the channel we have identified in these cells belongs to the maxi-K+ channel class.

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Sixteen synthetic or plant-derived coumarins of dietary importance with different patterns of substitution were tested for their capacity to scavenge superoxide and for their cytotoxicity. Superoxide was generated by human polymorphonuclear leukocytes stimulated by phorbol myristate acetate and was measured using the reduction of ferricytochrome c or of nitrobule tetrazolium (NBT). Eleven of the coumarins, all lacking dihydroxy substitution, did not scavenge superoxide. Of the remaining five, the most potent scavenger was fraxetin (7,8-dihydroxy-6-methoxycoumarin) with an IC50 (concentration producing 50% inhibition) of 2.3 microM in the cytochrome assay and 5.8 microM using NBT. The other four coumarins (all containing ortho-dihydroxy catechol functions, and found previously to be pro-oxidant in cell-free systems by virtue of reduction of ferric to ferrous ions), themselves rapidly reduced cytochrome c. Therefore their effects on superoxide were measured using NBT, yielding IC50 values in the range 8.5 to 82.0 microM. Fraxetin and the other active and inactive coumarins were not directly cytotoxic at 100 microM to leukocytes or to erythrocytes, as shown by their failure to cause release of cytosolic lactate dehydrogenase or to cause haemolysis, respectively. However, all five dihydroxylated pro-oxidant coumarins were toxic to NS20Y neuroblastoma cells in 24 hr culture, whereas the other eleven coumarins were nontoxic. We conclude that 7,8-dihydroxylated coumarins such as fraxetin are agents which are not themselves directly cytotoxic and are capable of direct scavenging of superoxide anion radicals, an action which might be protective at sites of leukocyte activation during inflammation. However, in the presence of free ferric ions they may exert potentially damaging pro-oxidant actions, including cytotoxicity. This series of compounds provides a useful basis for structure-activity studies designed to achieve separation or combination of these properties.

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Workers who do not recover as expected from job-related injuries are frequently disabled not by organic complications of their injuries but by a problem that the patient may not acknowledge and the physician may not recognize and deal with. The family physician should be skilled in detecting nonorganic causes of disability and in intervening appropriately to maintain a therapeutic relationship between the patient and the health care providers.

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The incidence of recombinational DNA repair and inducible mutagenic DNA repair has been examined in Escherichia coli and 11 related species of enterobacteria. Recombinational repair was found to be a common feature of the DNA repair repertoire of at least 6 genera of enterobacteria. This conclusion is based on observations of (i) damage-induced synthesis of RecA-like proteins, (ii) nucleotide hybridization between E. coli recA sequences and some chromosomal DNAs, and (iii) recA-negative complementation by plasmids showing SOS-inducible expression of truncated E. coli recA genes. The mechanism of DNA damage-induced gene expression is therefore sufficiently conserved to allow non-E. coli regulatory elements to govern expression of these cloned truncated E. coli recA genes. In contrast, the process of mutagenic repair, which uses umuC+ umuD+ gene products in E. coli, appeared less widespread. Little ultraviolet light-induced mutagenesis to rifampicin resistance was detected outside the genus Escherichia, and even within the genus induced mutagenesis was detected in only 3 out of 6 species. Nucleotide hybridization showed that sequences like the E. coli umuCD+ gene are not found in these poorly mutable organisms. Evolutionary questions raised by the sporadic incidence of inducible mutagenic repair are discussed.

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A plasmid-encoded E. coli lexA+ gene was introduced into 6 species of Enterobacteria. Ultraviolet light-sensitization occurred in all species except P. rettgeri, and 4 organisms showed reduced inducibility of RecA-like proteins. The mechanism of lexA+ control of the SOS response therefore appears common to several species.

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