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 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A procedure has been developed for measuring the steady state rate of permeation of commercial solvents through living human skin. To get the most consistent results, it was necessary with some solvents to normalize the solvent permeation rate of a given skin sample with its [3H]water permeation rate. For other solvents this was not necessary, so the un-normalized data were used. High [3H]water permeation rate also was used as a criterion for "defective" skin samples that gave erroneous permeability rates, especially for solvents having slow permeability. The linearity of the steady state data was characterized by calculation of the "percent error of the slope." The following permeability rates (g/m2h) of single solvents were measured: dimethyl sulfoxide (DMSO), 176; N-methyl-2-pyrrolidone, 171; dimethyl acetamide, 107; methyl ethyl ketone, 53; methylene chloride, 24; [3H]water, 14.8; ethanol, 11.3; butyl acetate, 1.6; gamma-butyrolactone, 1.1; toluene, 0.8; propylene carbonate, 0.7; and sulfolane, 0.2. The effect of [3H]water saturation on the shape of the presteady state portion of the permeation curve was determined and found to be very dependent on the solvent. The permeability of mixtures of DMSO and octyl acetate were measured. No octyl acetate was detected and the permeability of DMSO was proportional to its mole fraction in the mixture. The effect of two hours of solvent exposure on the viability of skin (based on DNA synthesis) was measured and found to be very dependent on the solvent.
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PMID:Permeability of commercial solvents through living human skin. 761 4

Single-channel currents through GABA- and glycine-activated chloride channels of post-natal tissue-cultured hippocampal neurons were measured to determine their anion selectivity and their concentration dependence of permeation. Current-voltage relations for both agonists displayed rectification with single-channel conductance increasing at positive potentials. Permeabilities determined from reversal potentials were maximal for anions with a diameter of about 4 A. Larger diameter anions had lower permeabilities, consistent with an approximate pore diameter of 6 A for both agonist-activated channels. The permeability for anions of similar size was greatest for those ions with a more symmetrical charge distribution (e.g. NO3- > Bicarbonate-). The permeability sequence was SCN- > NO3- > I- > Br- > Cl- > Formate- > Acetate- > Bicarbonate- > Gluconate- > F- > Phosphate-, whereas the conductance sequence for anion efflux was Cl- > Br- > NO3- > I- > SCN- > Formate- > Acetate- > Bicarbonate- > Gluconate- > F- > Phosphate-. These results suggest that the ions interact with sites within the channel, with hydration forces contributing an important component to the barrier for ion entry into the channel. The spherically symmetrical halides displayed an exponential relation between relative permeability and hydration energy. Concentration dependence of conductance for Cl- channels in symmetrical Cl- solutions with agonist in the pipette showed an increase at positive potentials and a decrease at negative potentials. GABA- and glycine-activated channels also exhibited anomalous mole-fraction effects in a mixture of Cl- and SCN-. These results suggest that both agonist-activated channels act as multi-ion pathways and have similar permeation characteristics.
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PMID:Anion permeation in GABA- and glycine-gated channels of mammalian cultured hippocampal neurons. 769 Apr 84

Gas chromatography was employed to quasi-continuously determine the amount of carbon dioxide that evolved from carbonate apatite specimens during sintering. Assuming that the carbonate in the specimens decomposed to carbon dioxide on a mole-for-mole basis, the determination of the carbon dioxide evolved allowed for the determination of the amount of carbonate that remained in the specimens during different stages of sintering. Previously, this measurement could be carried out only after sintering was completed. Comparison of data obtained from specimens compacted isostatically at 600 MPa for sintering with powder specimens indicated that the amount of carbonate remaining in the sintered apatite mass strongly depended on heating rates, heating temperatures, and holding-time intervals.
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PMID:Pyrolysis-gas chromatography of carbonate apatites used for sintering. 858 14

A distinctive feature of the voltage-dependent chloride channels ClC-0 (the Torpedo electroplaque chloride channel) and ClC-1 (the major skeletal muscle chloride channel) is that chloride acts as a ligand to its own channel, regulating channel opening and so controlling the permeation of its own species. We have now studied the permeation of a number of foreign anions through ClC-1 using voltage-clamp techniques on Xenopus oocytes and Sf9 cells expressing human (hClC-1) or rat (rClC-1) isoforms, respectively. From their effect on channel gating, the anions presented in this paper can be divided into three groups: impermeant or poorly permeant anions that can not replace Cl- as a channel opener and do not block the channel appreciably (glutamate, gluconate, HCO3-, BrO3-); impermeant anions that can open the channel and show significant block (methanesulfonate, cyclamate); and permeant anions that replace Cl- at the regulatory binding site but impair Cl- passage through the channel pore (Br-, NO3-, ClO3-, I-, ClO4-, SCN-). The permeability sequence for rClC-1, SCN- approximately ClO4- > Cl- > Br- > NO3- approximately ClO3- > I- >> BrO3- > HCO3- >> methanesulfonate approximately cyclamate approximately glutamate, was different from the sequence determined for blocking potency and ability to shift the Popen curve, SCN- approximately ClO4- > I- > NO3- approximately ClO3- approximately methanesulfonate > Br- > cyclamate > BrO3- > HCO3- > glutamate, implying that the regulatory binding site that opens the channel is different from the selectivity center and situated closer to the external side. Channel block by foreign anions is voltage dependent and can be entirely accounted for by reduction in single channel conductance. Minimum pore diameter was estimated to be approximately 4.5 A. Anomalous mole-fraction effects found for permeability ratios and conductance in mixtures of Cl- and SCN- or ClO4- suggest a multi-ion pore. Hydrophobic interactions with the wall of the channel pore may explain discrepancies between the measured permeabilities of some anions and their size.
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PMID:Permeation and block of the skeletal muscle chloride channel, ClC-1, by foreign anions. 956 3

The driving force for Cl- secretion in the salivary acinar cell is believed to be provided by the secondary active uptake of Cl- by Na+ dependent basolateral transporters. The energy cost of primary fluid secretion should therefore reflect the ratio of Na+ entry per mole of Cl- secreted. In the present study, we measured oxygen consumption (QO2) and fluid secretion in perfused mandibular and parotid glands from the rat, and estimated the energy cost of fluid secretion as the ratio of deltaQO2/delta(fluid secretion). During acetylcholine stimulation, the energy cost of fluid secretion by secretory endpieces was higher in the parotid gland than in the mandibular gland. The excess energy cost in the parotid gland may be attributable to other costs than the fluid and electrolyte transport. During bicarbonate-free perfusion in the mandibular gland, bumetanide abolished fluid secretion and QO2 decreased by ca 35%. The remaining QO2 was attributed to Na+ transport activity by basolateral antiports. Assuming values for the energy costs of each transporter and applying these to the total energy cost of the endpieces, the fraction of the total Na+ flux due to Na+/K+/2Cl- cotransport in Na+ handling was estimated to be 0.67. On the other hand, during perfusion with bicarbonate, after subtraction of the bumetanide-sensitive QO2 and the QO2 for antiports, about 19 microl/g/min of QO2 remained, which may be due to activation of Na+/HCO3- cotransport. Thus the inclusion of bicarbonate in the perfusate appears to alter the relative contributions of the various Na+-dependent basolateral transporters to total Na+ handling.
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PMID:Energy consumption associated with fluid and electrolyte transport in the mandibular and parotid glands. 982 7

It has recently been noted that a diversity of hyperthermophilic microorganisms have the ability to reduce Fe(III) with hydrogen as the electron donor, but the reduction of Fe(III) or other metals by these organisms has not been previously examined in detail. When Pyrobaculum islandicum was grown at 100 degrees C in a medium with hydrogen as the electron donor and Fe(III)-citrate as the electron acceptor, the increase in cell numbers of P. islandicum per mole of Fe(III) reduced was found to be ca. 10-fold higher than previously reported. Poorly crystalline Fe(III) oxide could also serve as the electron acceptor for growth on hydrogen. The stoichiometry of hydrogen uptake and Fe(III) oxide reduction was consistent with the oxidation of 1 mol of hydrogen resulting in the reduction of 2 mol of Fe(III). The poorly crystalline Fe(III) oxide was reduced to extracellular magnetite. P. islandicum could not effectively reduce the crystalline Fe(III) oxide minerals goethite and hematite. In addition to using hydrogen as an electron donor for Fe(III) reduction, P. islandicum grew via Fe(III) reduction in media in which peptone and yeast extract served as potential electron donors. The closely related species P. aerophilum grew via Fe(III) reduction in a similar complex medium. Cell suspensions of P. islandicum reduced the following metals with hydrogen as the electron donor: U(VI), Tc(VII), Cr(VI), Co(III), and Mn(IV). The reduction of these metals was dependent upon the presence of cells and hydrogen. The metalloids arsenate and selenate were not reduced. U(VI) was reduced to the insoluble U(IV) mineral uraninite, which was extracellular. Tc(VII) was reduced to insoluble Tc(IV) or Tc(V). Cr(VI) was reduced to the less toxic, less soluble Cr(III). Co(III) was reduced to Co(II). Mn(IV) was reduced to Mn(II) with the formation of manganese carbonate. These results demonstrate that biological reduction may contribute to the speciation of metals in hydrothermal environments and could account for such phenomena as magnetite accumulation and the formation of uranium deposits at ca. 100 degrees C. Reduction of toxic metals with hyperthermophilic microorganisms or their enzymes might be applied to the remediation of metal-contaminated waters or waste streams.
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PMID:Reduction of Fe(III), Mn(IV), and toxic metals at 100 degrees C by Pyrobaculum islandicum. 1069 70

Five 100 g batches of a carbonate apatite (the intermediate) were produced by heating an aqueous slurry of CaCO3 and CaHPO4 with an overall Ca/P mole ratio of 5/3 with vigorous stirring. Each intermediate produced by boiling off water was heated in vacuum at 1100 degrees C to remove carbonate, then steamed at 900 degrees C to ensure complete hydroxylation. Comparison of calculated and observed X-ray diffraction patterns showed final products containing 50-100 wt% monoclinic hydroxyapatite (remainder hexagonal). Rietveld refinements in P6(3)/m gave structures similar to several hydroxyapatite standards, including NIST SRM 2910, although there was no evidence from X-ray diffraction that the latter was in the monoclinic form. Refinements from standards and final products were slightly different from published single crystal data for Holly Springs hydroxyapatite. This is attributed to known impurities in mineral hydroxyapatite and indicates that parameters from the Rietveld refinements are closer to the true values for pure hydroxyapatite. Rietveld refinements for intermediates showed small, but significant differences from the final product, the largest being in O1x, O2x and O(H)z. All P-O bond lengths were shorter than in the final product, resulting in a 3.2% lower PO4 tetrahedron volume. The occupancies of P and Ca(2) were reduced. These differences are attributed to partial replacement of PO4(3) by CO3(2-) ions.
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PMID:Preparation and characterisation of monoclinic hydroxyapatite and its precipitated carbonate apatite intermediate. 1070 62

A quantitative analysis of O2 and CO2 transport was conducted in resting and exercising rainbow trout, and these data were used to quantify the magnitude of coupling between O2 and CO2 exchange, in vivo. The release of Bohr protons during haemoglobin-oxygenation was non-linear over the Hb-O2 equilibrium curve used in trout subjected to different levels of sustained exercise. At low swimming speeds, when venous blood O2 content (CvO2) was high, there was a small acidosis as blood passed through the gills, indicating more protons were released during oxygenation of Hb than were consumed during HCO3- dehydration. At higher swimming speeds, when CvO2 was low, there was a significant alkalosis in arterial relative to venous blood, indicating that fewer protons were released upon oxygenation than HCO3- ions were dehydrated to CO2. Haldane coefficients (moles of protons released per mole of O2 which binds to Hb), calculated from steady state arterial and mixed-venous parameters, revealed that under resting conditions all blood CO2 removed from the blood during gill transit was stoichiometrically related to O2 uptake through the release of Bohr protons during Hb oxygenation. The magnitude of coupling between CO2 excretion and O2 uptake decreased from 100% to less than 40% at the maximal swimming velocity when the largest region of the Hb-O2 equilibrium curve was used for gas exchange. The non-linear release of Bohr protons over the range of Hb-O2 saturation in the blood reduces HCO3- dehydration at the gills during greater work loads elevating arterial P(CO2) levels, leading to an increase in HCO3- buffer capacity of the blood and tissues.
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PMID:The interaction between O2 and CO2 exchange in rainbow trout during graded sustained exercise. 1070 10

The surfaces of six biologically interesting calcium phosphate (CaP) phases (hydroxyapatite, dibasic calcium phosphate dihydrate, dibasic calcium phosphate, monobasic calcium phosphate, beta-tribasic calcium phosphate, octacalcium phosphate) have been examined by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). The intensity of an O(1s) shake-up satellite correlates with the phosphate oxygen content. Together with the Ca/P and O/Ca XPS peak ratios, this feature helps provide identification of the CaP phase(s) present in the surface of unknown samples and establish their mole fractions, as proven with a bone sample. Contributions from carbonate impurities can be quantified using its C(1s) peak at 279.9 eV and subtracted from the O(1s) line shape to aid identification. Principal component analysis (PCA) has been applied successfully to analyze TOF-SIMS spectra of these six CaP phases. Multivariate analysis can help differentiate these CaP phases using the first two PCs, which are dominated by the relative intensities of only a few key ions: PO3-, O-, Ca+, CaOH+, PO2-, and OH-.
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PMID:Surface characterization of hydroxyapatite and related calcium phosphates by XPS and TOF-SIMS. 1090 23

Short-term imbalances in the global cycle of shallow water calcium carbonate deposition and dissolution may be responsible for much of the observed Pleistocene change in atmospheric carbon dioxide content. However, any proposed changes in the alkalinity balance of the ocean must be reconciled with the sedimentary record of deep-sea carbonates. The possible magnitude of the effect of shallow water carbonate deposition on the dissolution of pelagic carbonate can be tested using numerical simulations of the global carbon cycle. Boundary conditions can be defined by using extant shallow water carbonate accumulation data and pelagic carbonate deposition/dissolution data. On timescales of thousands of years carbonate deposition versus dissolution is rarely out of equilibrium by more than 1.5 x 10(13) mole yr-1. Results indicate that the carbonate chemistry of the ocean is rarely at equilibrium on timescales less than 10 ka. This disequilibrium is probably due to sea level-induced changes in shallow water calcium carbonate deposition/dissolution, an interpretation that does not conflict with pelagic sedimentary data from the central Pacific.
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PMID:Influence of variable rates of neritic carbonate deposition on atmospheric carbon dioxide and pelagic sediments. 1154 Feb 40


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