Functional properties of a truncated recombinant GIRK5 potassium channel

Xenopus laevis oocytes codify a G-protein-activated inward rectifier potassium channel (GIRK5 or Kir3.5). Coinjection of other GIRKs, the muscarinic m2 receptor, or Gbetagamma protein cRNAs is required to observe functional GIRKx-GIRK5 heteromultimers in oocytes. Studies with GIRK2 isoforms have shown that the size of the amino or carboxyl terminus plays a crucial role on giving functional K(+) channels. In this work we studied the properties of a GIRK5 with 25 amino acids deleted toward its amino-terminal domain. Injection of GIRK5-Delta25 cRNA alone displayed large basal and transient inward rectifying currents in oocytes. The instantaneous currents reached a stationary level after a long duration voltage pulse (10 s). For this relaxation, fast (tau(1)) and slow (tau(2)) time constants were estimated at different voltages. Recovery from inactivation followed a monoexponential function (tau=0.95+/-0.07 s). By contrast with other inward rectifier channels, blockade of GIRK5-Delta25 by extracellular Ba(2+) was voltage-independent (K(d)=102+/-2 microM), suggesting the presence of a Ba(2+) site at the external channel vestibule. To confirm this hypothesis, the Ba(2+) sensitivity of two charged mutants GIRK5-Delta25(N129E) and GIRK5-Delta25(K157E) at each of the external loops was determined. GIRK5-Delta25(N129E) and GIRK5-Delta25(K157E) showed a 100-fold and 2-fold higher affinity to Ba(2+), respectively, supporting the existence of this Ba(2+) binding site.

Detection of alkali metal ions in DNA crystals using state-of-the-art X-ray diffraction experiments

The observation of light metal ions in nucleic acids crystals is generally a fortuitous event. Sodium ions in particular are notoriously difficult to detect because their X-ray scattering contributions are virtually identical to those of water and Na(+.)O distances are only slightly shorter than strong hydrogen bonds between well-ordered water molecules. We demonstrate here that replacement of Na(+) by K(+), Rb(+) or Cs(+) and precise measurements of anomalous differences in intensities provide a particularly sensitive method for detecting alkali metal ion-binding sites in nucleic acid crystals. Not only can alkali metal ions be readily located in such structures, but the presence of Rb(+) or Cs(+) also allows structure determination by the single wavelength anomalous diffraction technique. Besides allowing identification of high occupancy binding sites, the combination of high resolution and anomalous diffraction data established here can also pinpoint binding sites that feature only partial occupancy. Conversely, high resolution of the data alone does not necessarily allow differentiation between water and partially ordered metal ions, as demonstrated with the crystal structure of a DNA duplex determined to a resolution of 0.6 A.

Van't Hoff and calorimetric enthalpies from isothermal titration calorimetry: are there significant discrepancies?

The enthalpy of a reaction is most often determined through one of two means; it can be determined directly using calorimetry or indirectly by measuring the temperature dependence of the equilibrium constant (i.e., the van't Hoff method). Recently, discrepancies have been noted between the enthalpy measured by calorimetry, and the enthalpy determined by the van't Hoff method,. This has been suggested to indicate that the binding reaction is more complex than the simple one-to-one binding model used to describe the data. To better understand possible discrepancies between and, we have undertaken both experimental studies using isothermal titration calorimetry to measure the binding energetics of Ba(2+) binding 18-crown-6 ether and 2'-CMP binding RNase A, along with a simulation of a system involving a molecule in conformational equilibrium coupled with binding. We find that when experimental setup and analysis are correctly performed, no statistically significant discrepancies between and exist even for the linked system.

Characterisation of mineralogical forms of barium and trace heavy metal impurities in commercial barytes by EPMA, XRD and ICP-MS

This study was carried out to characterise the mineralogical forms of barium and the trace heavy metal impurities in commercial barytes of different origins using electron probe microanalysis (EPMA), X-ray diffraction (XRD) and inductively coupled plasma mass spectrometry (ICP-MS). Qualitative EPMA results show the presence of typically eight different minerals in commercial barytes including barite (BaSO4), barium feldspar, galena (PbS), pyrite (FeS2), sphalerite (ZnS), quartz (SiO2), and silicates, etc. Quantitative EPMA confirms that the barite crystals in the barytes contain some strontium and a little calcium, whereas trace heavy metals occur in the associated minerals. Analysis of aqua regia extracts of barytes samples by ICP-MS has shown the presence of a large number of elements in the associated minerals. Arsenic, copper and zinc concentrations correlate closely in all 10 samples. The findings suggest that barytes is not, as traditionally thought, an inert mineral, but is a potentially toxic substance due to its associated heavy metal impurities, which can be determined by an aqua regia digest without the need for complete dissolution of the barite itself. X-ray powder diffraction was not informative as the complex barite pattern masks the very weak lines from the small amounts of associated minerals.

Removal of an airborne low volatility metal under fuel-rich and fuel lean conditions through condensation onto soot and/or sorbent particles

The removal by a sorbent of a low volatility heavy metal, barium, from a combustor exhaust stream was investigated experimentally. The barium was introduced into the gas phase through a combustion process simulating incineration of waste materials. Sorbent- and metal-feed-rate, temperature and air intake were varied to study the impact on the gas-to-particle conversion and the metal condensation process. Peak temperature and subsequent temperature drop were found to be the dominant factors affecting the condensation process. Fuel-rich and fuel-lean conditions result in lower peak temperatures and a more rapid temperature drop relative to stoichiometric conditions. Since the metal vapor saturation pressure falls exponentially with temperature a larger condensation rate was observed, as long as nucleation was suppressed. Fuel-rich conditions promote the formation of soot particles. These particles function as sites for subsequent metal-species condensation. Chlorine was injected into the flow, to study the effect on metal vaporization. Chlorine promoted the volatilization of barium and therefore the subsequent condensation capture was made more effective.

Synthesis and complexation properties of poly(ethylene glycol)-linked mono- and bis-dioxocyclams

Both tri- and tetra(ethylene glycol) linked bis-chromium carbene complexes have been synthesized. These carbene complexes were photolyzed with N-protected imidazolines to give protected azapenams. These were transformed into polyether-linked basket dioxocyclams 4a,b and bis-dioxocyclams 5a,b. These compounds have cavities for the complexation of both "hard" and "soft" metal ions. The complexes of Ni, Ba, and Gd were synthesized.

How can Ca2+ selectively activate recoverin in the presence of Mg2+? Surface plasmon resonance and FT-IR spectroscopic studies

We investigated the relationship between metal ion selective conformational changes of recoverin and its metal-bound coordination structures. Recoverin is a 23 kDa heterogeneously myristoylated Ca(2+)-binding protein that inhibits rhodopsin kinase. Upon accommodating two Ca(2+) ions, recoverin extrudes a myristoyl group and associates with the lipid bilayer membrane, which was monitored by the surface plasmon resonance (SPR) technique. Large changes in SPR signals were observed for Sr(2+), Ba(2+), Cd(2+), and Mn(2+) as well as Ca(2+), indicating that upon binding to these ions, recoverin underwent a large conformational change to extrude the myristoyl group, and thereby interacted with lipid membranes. In contrast, no SPR signal was induced by Mg(2+), confirming that even though it accommodates two Mg(2+) ions, recoverin does not induce the large conformational change. To investigate the coordination structures of metal-bound Ca(2+) binding sites, FT-IR studies were performed. The EF-hands, Ca(2+)-binding regions each comprising 12 residues, arrange to coordinate Ca(2+) with seven oxygen ligands, two of which are provided by a conserved bidentate Glu at the 12th relative position in the EF-hand. FT-IR analysis confirmed that Sr(2+), Ba(2+), Cd(2+), and Mn(2+) were coordinated to COO(-) of Glu by a bidentate state as well as Ca(2+), while coordination of COO(-) with Mg(2+) was a pseudobridging state with six-coordinate geometry. These SPR and FT-IR results taken together reveal that metal ions with seven-coordinate geometry in the EF-hands induce a large conformational change in recoverin so that it extrudes the myristoyl group, while metal ions with six-coordinate geometry in the EF-hands such as Mg(2+) remain the myristoyl group sequestered in recoverin.

Ca2+-assisted, direct hydride transfer, and rate-determining tautomerization of C5-reduced PQQ to PQQH2, in the oxidation of beta-D-glucose by soluble, quinoprotein glucose dehydrogenase

Spectral and kinetic studies were performed on enzyme forms of soluble glucose dehydrogenase of the bacterium Acinetobacter calcoaceticus (sGDH) in which the PQQ-activating Ca(2+) was absent (Holo X) or was replaced with Ba(2+) (Ba-E) or in which PQQ was replaced with an analogue or a derivative called "nitroPQQ" (E-NPQ). Although exhibiting diminished rates, just like sGDH, all enzyme forms were able to oxidize a broad spectrum of aldose sugars, and their reduced forms could be oxidized with the usual artificial electron acceptor. On inspection of the plots for the reductive half-reaction, it appeared that the enzyme forms exhibited a negative cooperativity effect similar to that of sGDH itself under turnover conditions, supporting the view that simultaneous binding of substrate to the two subunits of sGDH causes the effect. Stopped-flow spectroscopy of the reductive half-reaction of Ba-E with glucose showed a fluorescing transient previously observed in the reaction of sGDH with glucose-1-d, whereas no intermediate was detected at all in the reactions of E-NPQ and Holo X. Using hydrazine as a probe, the fluorescing C5 adduct of PQQ and hydrazine was formed in sGDH, Ba-E, and Holo X, but E-NPQ did not react with hydrazine. When this is combined with other properties of E-NPQ and the behavior of enzyme forms containing a PQQ analogue, we concluded that the catalytic potential of the cofactor in the enzyme is not determined by its adduct-forming ability but by whether it is or can be activated with Ca(2+), activation being reflected by the large red shift of the absorption maximum induced by this metal ion when binding to the reduced cofactor in the enzyme. This conclusion, together with the observed deuterium kinetic isotope effect of 7.8 on transient formation in Ba-E, and that already known on transient decay, indicate that the sequential steps in the mechanism of sGDH must be (1) reversible substrate binding, (2) direct transfer of a hydride ion (reversible or irreversible) from the C1 position of the beta-anomer of glucose to the C5 of PQQ, (3) irreversible, rate-determining tautomerization of the fluorescing, C5-reduced PQQ to PQQH(2) and release (or earlier) of the product, D-glucono-delta-lactone, and (4) oxidation of PQQH(2) by an electron acceptor. The PQQ-activating Ca(2+) greatly facilitates the reactions occurring in step 2. His144 may also play a role in this by acting as a general base catalyst, initiating hydride transfer by abstracting a proton from the anomeric OH group of glucose. The validity of the proposed mechanism is discussed for other PQQ-containing dehydrogenases.

Principal component analysis of the absorption and resonance Raman spectra of the metallochromic indicator antipyrylazo III

Metallochromic indicators, whose spectral properties are changed in the presence of metal cations, are used mainly in biological studies to monitor Ca2+ and Mg2+ ions. Antipyrylazo III is such indicator, employed for mid-range Ca2+ concentrations (10-1000 microM). The stoichiometry of the interactions of antipyrylazo III with Ca2+, Mg2+, Ba2+, Sr2+ and Zn2+ ions and the relevant binding constants were studied by principal component analysis (PCA) of the absorption spectral changes. The resonance Raman spectra of the above systems were measured as well, and the resolved Raman spectra of the various species were calculated and assigned. The vibrational spectra are more featured, more characteristic of the binding ions and exhibit stronger relative spectral changes upon binding the cations. The basis sets of Raman spectra could thus be used as an analytical tool for these divalent metallic cations.

Sugar interaction with metal ions. FT-IR study on the structure of crystalline galactaric acid and its K+, NH4+, Ca2+, Ba2+, and La3+ complexes

The FT-IR spectra of galactaric acid and its K+, NH4+, Ca2+, Ba2+, and La3+ salts have been recorded and interpreted. Spectroscopic evidence shows that the dimeric carboxylic groups of the free acid are dissociated upon formation of the salt, and the asymmetric and symmetric stretching vibrations of the anionic COO- group in these salts are observed at about 1600 and 1400 cm-1, respectively. The two carboxylic groups of the galactarate coordinate with Ca2+ ions in a monodentate form. One of the carboxylic groups in the Ba2+ salt coordinates in a monodentate state; another group interacts with three cations in a tetradentate form. In the K+, NH4+, and La3+ salts, the COO- groups coordinate in a polydentate manner with the cations. By comparison of the spectra of the salts with that of the free acid, it is concluded that the hydroxyl groups of the galactarate skeleton take part in metal-oxygen interaction, and the hydrogen-bonding network is rearranged upon sugar metalation. The degree of participation of the sugar OH groups in metal-galactarate interaction is varied from the K+ and NH4+ salts to the Ca2+, Ba2+, and La3+ salts.

NMR, UV-vis and CD study on the interaction of pradimicin BMY-28864 with divalent cations of alkaline earth metal

In order to clarify the mechanism of the calcium-activated anti-fungal action of pradimicin derivatives, we investigated the compatibility of four divalent metal cations, Ca2+, Mg2+, Sr2+ and Ba2+, when combined with pradimicin BMY-28864 in an aqueous solution. The 1H NMR studies suggest that all the tested cations can induce a chemical exchange between two types of aggregation of BMY-28864 in an aqueous solution. The exchange rate, however, varies according to the cation species. In descending order they are: Ba2+ > Sr2+ > Ca2+ > Mg2+. The differences in the binding ability of BMY-28864 to the cations and the solubility of the chloride salts are explained by the electronegativity of these cations. The UV-Vis and CD spectra of these solutions show isosbestic points that correspond to an exchange process in the cations' binding to BMY-28864. The results provide experimental support for the hypothesis that there is a common mechanism underlying their cations interactions with the antibiotic. The CD study also provided evidence about the stoichiometric relation of the divalent metal ions to the antibiotic, 1:2, which was obtained by NMR analyses.

Ion exchangers in radioactive waste management. Part XI. Removal of barium and strontium ions from aqueous solutions by hydrous ferric oxide

The uptake of Ba(II) and Sr(II) by hydrous ferric oxide (HFO) was studied as a function of contact time, concentration, temperature and pH of the respective adsorptive solutions employing the 'radiotracer technique'. The uptake of both the ions was found to increase with the increase in concentration, temperature and pH of the adsorptive solutions. Concentration dependence data fitted well to the Freundlich adsorption isotherm over the entire range of concentration (10(-2)-10(-7) M) and the uptake process followed first-order rate kinetics. The desorption experiments demonstrate the irreversible nature of the uptake process, however, in the presence of H+ ions, i.e. on acidification, an appreciable amount of metal ions were removed in the bulk solution. The radiation stability of hydrous ferric oxide towards the uptake of Ba(II) and Sr(II) was also examined by using samples of hydrous ferric oxide irradiated by neutrons and gamma-rays prior to be employing as sorbents. The presence of some mono- and divalent co-ions along with the studied ions suppressed their removal appreciably.

Dielectric properties of alginate beads and bound water relaxation studied by electrorotation

The electrical and dielectric properties of Ba2+ and Ca2+ cross-linked alginate hydrogel beads were studied by means of single-particle electrorotation. The use of microstructured electrodes allowed the measurements to be performed over a wide range of medium conductivity from about 5 mS/m to 1 S/m. Within a conductivity range, the beads exhibited measurable electrorotation response at frequencies above 0.2 MHz with two well-resolved co- and antifield peaks. With increasing medium conductivity, both peaks shifted toward higher frequency and their magnitudes decreased greatly. The results were analyzed using various dielectric models that consider the beads as homogeneous spheres with conductive loss and allow the complex rotational behavior of beads to be explained in terms of conductivity and permittivity of the hydrogel. The rotation spectra could be fitted very accurately by assuming (a) a linear relationship between the internal hydrogel conductivity and the medium conductivity, and (b) a broad internal dispersion of the hydrogel centered between 20 and 40 MHz. We attribute this dispersion to the relaxation of water bound to the polysaccharide matrix of the beads. The dielectric characterization of alginate hydrogels is of enormous interest for biotechnology and medicine, where alginate beads are widely used for immobilization of cells and enzymes, for drug delivery, and as microcarriers for cell cultivation.

Characterization of the YbBa2Cu3O7-y and YBa2Cu3O7-y thin superconducting films prepared by chemical solution deposition on MgO(001) substrate

Thin superconducting films of the YbBa2Cu3O7-y (Yb123) and YBa2Cu3O7-y (Y123), prepared by post-deposition annealing of the metal naphthenates gels spin-coated on MgO(001) substrate, have been characterized by cross-sectional high-resolution electron microscopy and X-ray diffraction. It was found that the c-axis Yb123 films were epitaxially grown on the MgO(001) substrate at the temperature range from 700 degrees C to 775 degrees C in a gas mixture containing Ar and O2 with the oxygen partial pressure of p(O2) = 10(-4) atm. In contrast to the Yb123 films, it was found that Y123 films could be derived at a wider temperature range from 750 degrees C to 950 degrees C. Randomly oriented Y123 films were also grown on the MgO(001) substrate besides the majority of in-plane c-axis oriented growth.

Structural study of a lead-barium-aluminum phosphate glass by MAS-NMR spectroscopy

The 31P- and 27Al-MAS-NMR spectra of a lead-barium-aluminum phosphate glass were measured and analyzed, and the short range structure of the glass are discussed. The 31P-MAS-NMR spectrum of the glass studied has a single isotropic peak at -4.76 ppm, indicating that orthophosphate species are the dominant P-sites in the glass. The 27Al-MAS-NMR spectrum of the glass shows that the aluminum ions present in the glass are in 4-, 5-, and 6- fold coordination with oxygen, and that the Al(OP)4 is the dominant moiety for the glass, suggesting the formation of orthophosphate species in the glass.

[Safety health conditions for disposal of waste generated during the production of barium and boron compounds]

The authors proposed an approach to calculating maximum concentrations of dust in the ambient air that may occur during digging, loading and transportation of barium and boron wastes containing a variety of metallic compounds, including arsenic and nickel. In addition, they listed conditions which should be fulfilled in view of binding legal regulations, in order to ensure that the work performed does not create any health risk. It was recognized that maintaining dust concentrations in the air below 5 mg/m3 should protected workers against the potential risk during their work.

Inhibitory effect of lomerizine, a diphenylpiperazine Ca2+-channel blocker, on Ba2+ current through voltage-gated Ca2+ channels in PC12 cells

We investigated the effect of lomerizine, an anti-migraine drug, on the Ba2+ current through voltage-gated Ca2+ channels in rat pheochromocytoma (PC12) cells using a whole-cell voltage-clamp technique. Lomerizine inhibited the Ba2+ current with an IC50 value of 1.9 microM. Lomerizine and nicardipine were >4 times more potent than flunarizine, diltiazem, verapamil and dimetotiazine. The time course of inactivation induced by lomerizine was similar to that induced by nicardipine and flunarizine. These data indicate that lomerizine may inhibit the Ca2+ channel in a similar manner to nicardipine and flunarizine, and its potency is almost equal to that of nicardipine.

The effect of filler content and processing variables on dimensional accuracy of experimental composite inlay material

STATEMENT OF PROBLEM

Dimensional accuracy of a composite inlay restoration is important to ensure an accurate fit and to minimize cementation stresses.

PURPOSE OF STUDY

A method was developed to measure dimensional accuracy and stability of a composite inlay.

MATERIAL AND METHODS

A standard Class II (MOD) inlay cavity stainless steel mold was made with six circular indentations placed on the occlusal floor of the cavity and four indentations on each gingival floor to act as datum points in the measurement of linear polymerization shrinkage. The inlay restorations were prepared from an inlay-onlay composite material of different filler contents (50%, 65%, and 79% by weight). For each filler content group, three curing methods were used: light curing only, light curing and heat curing at 100 degrees C for 5 minutes, and light curing and heat curing at 100 degrees C for 5 minutes and then storage in distilled water for 7 days. The accuracy of the MOD inlays was determined by measuring the shrinkage of the restoration on the occlusal floor areas and the gingival seats.

RESULTS

The results demonstrated an inverse linear relationship between filler content and polymerization shrinkage. There was a tendency for the light-curing and heat-curing method to show an increase in polymerization shrinkage. An expansion was recorded between the mesial and distal boxes when the specimens were soaked in water for 7 days.

CONCLUSIONS

This study suggested that the inlay mold limits the physical shrinkage that can occur between the mesial and distal axial walls of the inlay restoration because the inlay cannot shrink to a smaller dimension than the mold. Water sorption then causes hygroscopic expansion, which enlarges the distance between the mesial and distal walls.

Specific regions of heteromeric subunits involved in enhancement of G protein-gated K+ channel activity

Heterologous coexpression of recombinant, G protein-gated, inwardly rectifying K+ (GIRK) channel subunits has yielded large currents, severalfold greater than those obtained from expression of the individual subunits. Such current enhancement has been obtained from coexpression of the inactive GIRK1 subunit with the low activity GIRK2-5 subunits in Xenopus oocytes. Using deletion and chimeric constructs, we now report the identification of a C-terminal region unique to GIRK1 and a larger central region of GIRK4 highly homologous to GIRK1, both of which are critical for production of large currents. Chimeras containing these two regions produced homomeric channels, exhibiting currents severalfold greater than those from either wild-type subunit alone. G protein regulation of such chimeric channel currents resembled that of wild-type currents. Green fluorescent protein-tagged channels showed that the amount of chimeric channel expressed on the oocyte cell surface was similar to its wild-type counterpart, suggesting that the enhanced activity was not due to differences in relative levels of expression but rather to the coexistence of the chimeric regions. Single-channel recordings of the active chimeras exhibited patterns of activities with open-time kinetics and conductance characteristics representative of those of GIRK4, indicating that the presence of the GIRK1 C-terminal region caused an increase in the frequency of channel openings without affecting their duration.

Potassium conductances and proliferation in conditionally immortalized renal glomerular mesangial cells from the H-2Kb-tsA58 transgenic mouse

The effects of the temperature-sensitive, immortalizing Simian Virus 40 T antigen, tsA58, on whole-cell potassium conductances were assessed in renal glomerular mesangial cells from H-2Kb-tsA58 transgenic mice [1]. MTT cell viability assay data indicated that in permissive (33 degrees C, 50 U ml-1 gamma-interferon, IFN+) and non-permissive (37 degrees C, without gamma-interferon, IFN-) culture conditions the oncogene was active and inactive respectively. In IFN+ cells whole-cell currents were inhibited by 10 mM 4-aminopyridine, 1 mM ATP and glibenclamide (glyburide, IC50 = 0.4 microM) and stimulated by cromakalim (EC50 = 40 microM). Furthermore, increases in pipette free calcium activity stimulated the potassium conductance (EC50 = 0.5 microM). Apamin inhibited this conductance (IC50 = 9 nM). None of these effects were observed in IFN- cells. The potassium conductance in IFN- cells was activated by a hyposmotic shock and this was inhibited by Gd3. These data indicate that (1) conductances consistent with ATP-sensitive and small, calcium-activated potassium channels are found in IFN+ cells, (2) an osmotically-sensitive channel is found in IFN- cells and (3) channel expression is dependent upon the activation of tsA58.

Effect of barium in porcelain on bonding strength of titanium-porcelain system

The bonding strength to titanium, thermal expansion, and bending strength of glassy porcelain containing barium of 5, 10, and 15 mass% were estimated and compared with those of barium-free porcelain, to estimate the effect of barium content on bonding strength to titanium. The three different glassy porcelains containing barium were made by melting at 950 degrees C. The bonding strength of a commercial porcelain to titanium increased with the addition of barium. Bending strength and thermal expansion were not affected by the barium content. Therefore, the addition of barium to porcelain is effective for strengthening the bonding of porcelain to titanium.

Activity-dependent ultra-slow inactivation of calcium currents in rat anterior pituitary cells

1. The inactivation of high-voltage-activated (HVA) calcium currents during long depolarizations in holding potential (Vh) was studied with the use of whole cell patch-clamp recording from rat anterior pituitary cells. 2. An ultra-slow inactivation in the amplitude of HVA calcium currents, with an average slow time constant of 149.3 s for peak currents and 159.1 s for sustained currents (n = 9), was unveiled during 5-min step depolarizations in Vh. 3. The ultra-slow inactivation of HVA calcium currents was found to be generated by at least two processes: a voltage-dependent inactivation that increases with increasing depolarization in Vh and an activity-dependent inactivation that is initiated, but not increased, with increasing depolarization in Vh. The relative contribution of the activity-dependent component to the ultra-slow inactivation was 80% when Vh was stepped from -80 to -60 mV and only 40% when Vh was stepped from -80 to -40 mV. 4. The activity-dependent inactivation of the HVA currents was not altered significantly in experiments in which barium replaced calcium as charge carrier and 1,2-bis (1-aminophenoxy) ethane N,N,N' N'-tetraacetic acid (BAPTA) was used as an intracellular calcium buffer instead of the less potent ethylenglycol-bis-(beta-aminoethylether) N,N,N' N'-tetraacetic acid (EGTA). In addition, activity-dependent inactivation was observed with sodium as the charge carrier through the calcium channels. 5. The activity-dependent inactivation depends on divalent cation influx. The activity-dependent inactivation was abolished when the test potentials, during the depolarization in Vh, were increased from 0 to +70 mV (close to the reversal potential for calcium currents under our experimental conditions). This reduction in driving force for calcium currents eliminated divalent cation influx and abolished the activity-dependent inactivation. 6. The activity-dependent inactivation lacks several characteristic features for calcium-dependent inactivation, such as dependence on charge carrier (see above), dependence on the size of the calcium current, and increase in decay rate of the calcium current during the test pulse. These latter notions were also supported by our paired pulse experiments, in which the calcium current elicited by a constant test pulse was virtually unaffected (7%) by conditioning pulses that produced maximal calcium currents. We therefore conclude that the dependence of activity-dependent inactivation on divalent cation influx cannot be attributed to the known form of calcium-dependent inactivation. 7. In conclusion, this study shows that calcium influx through HVA channels in anterior pituitary cells can be regulated by subthreshold changes in membrane potential and that the extent of this regulation depends on low-frequency activation of HVA calcium channels during the depolarization in membrane potential. Thus the pituitary cell may regulate hormone secretion by changes in membrane potential and in a use-dependent manner via regulation of calcium influx.

Electric quadrupole interaction of 137Ba in barium fluorohalides

The X-ray storage phosphor materials BaFC1 and BaFBr differ greatly in their 137Ba nuclear electric quadrupole interaction, despite a common crystal structure. The quadrupole coupling constant in BaFCl is relatively small and increases rapidly with temperature, in an unusual manner: [CQ[ = 1.7 MHz at T = 296 K, CQ-1(delta CQ/delta T)p = 1.7 x 10(-3) K-1. The coupling BaFBr is [CQ[ = 17.0 MHz at 296 K. The difference in quadrupole coupling at room temperature is explained using an electrostatic point-charge model of the crystals.

Laser-induced fluorescence of Ba+ ions trapped and mass-selected in a Fourier transform ion cyclotron resonance mass spectrometer

We present the design and preliminary results from a Fourier transform ion cyclotron resonance (ICR) mass spectrometer developed for the direct detection of UV/visible laser-induced fluorescence of trapped, mass-selected, gas-phase ions. A 3 T superconducting magnet and an open-ended multi-section cylindrical Penning trap capture and confine ions created by electron impact or laser desorption. Azimuthal quadrupolar excitation in the presence of ion/neutral collisions cools, axializes and mass selects ions as they fill the trap. A pulsed dye laser pumped by an Nd:YAG laser provides electronic energy excitation. A Brewster window and baffles on each side of the vacuum chamber reduce the scattered light from the excitation laser. Laser-induced fluorescence is collected from mirrors and lenses and directed through a quartz window and fiber-optic bundle to a photomultiplier. The ICR and optical events are controlled by a modular ICR data station and GPIB and RS-232 interfaces. An excitation spectrum is demonstrated for atomic Ba+ ions, and should extend to laser-induced fluorescence of virtually any stable positive or negative gas-phase ions of arbitrary molecular weight: molecular or quasimolecular ions, fragment ions, adduct ions, and ions formed from ion/molecule reactions.