ALBERT

Notizen: Summary The intestinal secretagogues ricinoleate and deoxycholate have been tested for a capacity to form complexes with Ca2+ ions and to affect the passive equilibration of Ca2+ ions across the jejunal brush border membrane. Both of these agents formed butanol-soluble Ca2+ complexes in a model phase distribution system. They also promote the passive uptake and efflux of Ca2+ across brush border vesicles in a concentrationdependent manner. The levels of ricinoleate and deoxycholate that increase the rate of transvesicular Ca2+ movement are in the 100 to 300 μm range. Concentrations as high as 1.0mm had no significant detergent effects in vesicles as measured by release of entrapped sorbitol. The kinetics of Ca2+ uptake and efflux are similar in brush border vesicles treated with A23187, ricinoleate, or deoxycholate. The influx rates observed in this study were high enough to cause the collapse of a Ca2+ gradient, which had been generated by Ca-Mg ATPase enzyme activity in the brush border membrane. Ricinoleate did not affect Ca-Mg ATPase activity at concentrations used in this study, but deoxycholate was inhibitory, indicating two potential modes for elevation of intracellular Ca2+ content by deoxycholate. When compared with the effects of the Ca2+ ionophore, A23187, it appears that both ricinoleate and deoxycholate could have significant intestinal secretory activity due to this Ca2+ ionophore property. It is also noteworthy that, at least in this model system, potential secretory effects are expressed at concentrations significantly below levels that have been associated with detergent effects or altered epithelial morphology.

Notizen: Abstract Using flow microcalorimetry, the ion association reaction M2+(aq)+Fe(CN) 6 4− (aq)=MFe(CN) 6 2− (aq) (M=Ca, Mg) has been studied at 25°C over the ionic strength range 0.02 to 0.08 mol-dm−3. Analyses of the data to obtain ΔHo, the enthalpy change at infinite dilution, are described. The value obtained for ΔHo is sensitive to the kind of functions used to correct for non-ideal behavior.

Notizen: Abstract It has been reported that, by adding equal amounts of CaO and CuO to non superconducting La3Ba3Cu6O z (La-336), a series of superconductors with nominal compositions La3Ca y Ba3Cu6+y O z were prepared with maximum Ton c ∼ 80K. Similar studies on addition of CaO and CuO in nonsuperconducting LaBaCu2O z (La-112) resulted into superconducting LaCaBaCu3O z (La-1113). To date no attempt has been made to synthesize La2CaBa2Cu5O z (La-2125) superconducting phase by addition of CaO and CuO to non superconducting La2Ba2Cu4O z (La-224) system. Also no reports are published to study the effect of replacing larger La3+-ions (1.01Å) by smaller rare earth ions viz Y3+(0.89Å), Er3+(0.91Å), Gd3+(0.91Å) on the structural and superconducting properties of (La2−x R x )Ba2(Ca y Cu4+y )O z (LRBCaC); 0.0 ≤ x ≤ 0.5; y=2x system. In this paper, we report the method of synthesis, structural and superconducting property characterization using X-ray diffraction, oxygen content measurements using iodometry, resistivity measurements using d.c. four probe technique and a.c. susceptibility measurements in the temperature range RT to 15K. Also a comparative study, on the evolution of superconducting phase with Ca-concentration for different rare earth substitutions for LRBCaC system in the context of hole doping mechanism, is carried out.

Notizen: Summary By subjecting isolated adrenal medullary cells to intense electric fields of brief duration it is possible to gain access to the cell interior without impairing the ability of the cell to undergo exocytosis. After a single exposure to a field of 2 kV/cm, τ=200 μsec, adrenal medullary cells behave as if their plasma membrane contains two pores of effective radius 2 nm. At 37°C these ‘equivalent pores’ remain patent for up to 1 hr. The formation and stability of these ‘pores’ is not affected by the Ca content of the bathing solution. The ‘pores’ permit externally applied catecholamine and Ca-EGTA to equilibrate rapidly with the cell water. Cells rendered ‘leaky’ in K glutamate medium containing 5mm Mg-ATP and EGTA to give an ionized Ca close to 10−8 m release less than 1% of their total catecholamine. These same cells can release up to 30% of their catecholamine when exposed to 10−5 m Ca. This Ca-dependent release is unaffected by Ca-channel blockers such as D600. Catecholamine release in response to a calcium challenge only seems to occur during the first few minutes whilst the Ca concentration is changing, and the extent of release depends on the final Ca concentration achieved. Half-maximal release occurs at about 1 μm Ca, and this value is independent of the EGTA concentration used to buffer the ionized Ca. The relation between ionized Ca and catecholamine release is best fitted by a requirement for 2 Ca ions. Calcium-evoked release of catecholamine is associated with the release of dopamine-β-hydroxylase (DβH) but not lactate dehydrogenase. The ratio DβH/catecholamine released is the same as that in stimulated intact cells and perfused glands. The time course of appearance in the external medium of DβH and catecholamine is identical. Transmission electron microscopy of ‘leaky’ cells exposed to 10−8 m Ca reveals no marked differences from unstimulated intact cells. The cytoplasm of ‘leaky’ cells exposed to 10−5 m Ca contains large membrane-bounded vacuoles. When secretion is caused to take place in the presence of horseradish peroxidase, this marker is found within the vacuoles. Ca-dependent release of both catecholamine and DβH requires Mg-ATP. Cells equilibrated with Ca in the absence of Mg-ATP can be triggered to undergo exocytosis by the addition of Mg-ATP. In the absence of Mg, ATP alone is ineffective. Of a variety of other nucleotides tested, none is as effective as ATP. Mg-ATP affects the extent of exocytosis and not its apparent affinity for Ca. Replacement of glutamate as the major anion by chloride results in a marked reduction in Ca-dependent release of both catecholamine and DβH. Chloride causes a small increase in Ca-independent release of catecholamine, a large reduction in the extent of exocytosis, and a decrease in the apparent affinity of exocytosis for Ca. Of a variety of anions examined, their order of effectiveness at supporting Ca-dependent exocytosis is glutamate−〉acetate−〉Cl−〉Br−〉SCN−. Exocytosis is not obviously affected by replacing K by Na or sucrose or by altering the pH over the range pH 6.6 to 7.8. Raising the free Mg concentration reduces the extent of Ca-dependent exocytosis and also its apparent affinity for calcium. Calcium-dependent exocytosis in ‘leaky’ cells is largely unaffected by (i) a variety of agonists and antagonists of the nicotinic receptor; (ii) agents that disrupt microtubules and microfilaments; (iii) phalloidin; (iv) vanadate; (v) inhibitors of anion permeability; (vi) protease inhibitors; and (vii) agents that dissipate the vesicle pH gradient and potential. It is partially inhibited by (i) certain antipsychotic drugs; (ii) a rise in osmotic pressure, (iii) lowering the temperature below 20°C, and (iv) N-ethyl maleimide.

Notizen: Abstract Experiments on parathyroidectomized cats with motor disorders of different degrees of severity showed disturbance of spinal reflex activity, in the form of activation of motoneurons and the interneuron system, weakening of posttetanic potentiation, and facilitation of conduction in the reflex arc. If severe tetany was present monosynaptic responses were reduced or, in some cases, abolished completely and polysynaptic reflex discharges were potentiated. After intravenous injection of calcium chloride into the experimental animals a tendency was found for recordable reflexes to return. It is concluded that disturbance of the functional state of the spinal segmental apparatus was largely due to hypocalcemia and it may be one of the causes of tetany in hypoparathyroidism.

Notizen: Abstract The involvement of the calcium and phosphoinositide intracellular regulatory systems in the molecular-cellular mechanisms of adaptation of the brain to hypoxia induced by transient anoxia were studied in slices of rat olfactory cortex. Anoxia lasting 2 min initiated the development of moderate but stable activation of intracellular regulatory systems during the reoxygenation period, with increases in binding of Ca2+ to intracellular hydrophobic domains and increases in the level of polyphosphoiositide metabolism. During this period, cells in the slices released neuromediator factors into the perfusion fluid; transfer of these to recipient slices induced similar changes in the activities of intracellular regulatory system components in the recipient slices. After anoxia lasting 10 min, NMDA-mediated pathogenic hyperactivity of the calcium and phosphoinositide systems developed. Preliminary moderate activation of these systems by transient anoxia or neuromodulator factors released by cells in response to transient anoxia prevented disruption of intracellular regulatory system activity induced by subsequent longer-lasting anoxia.

Notizen: Abstract The variability and biologicalfractionation of Sr/Ca, Ba/Ca and 87Sr/86Srratios were studied in a soil–plant–invertebrate–bird food chain in two forested ecosystems withcontrasting calcium availability in the northeasternU.S.A. Chemical measurements were made of the soilexchange pool, leaves, caterpillars, snails, and boththe femurs and eggshells of breeding insectivorousmigratory songbirds. 87Sr/86Sr values weretransferred up the food chain from the soil exchangepool to leaves, caterpillars, snails and eggshellswithout modification. Adult birds were the oneexception; their 87Sr/86Sr values generallyreflected those of lower trophic levels at each site,but were lower and more variable, probably becausetheir strontium was derived in part from foods intropical winter habitats where lower87Sr/86Sr ratios are likely to predominate. Sr/Ca and Ba/Ca ratios decreased at each successive trophiclevel, supporting previous suggestions that Sr/Ca andBa/Ca ratios can be used to identify the trophic levelat which an organism is primarily feeding. The changesin Sr/Ca and Ba/Ca ratios we measured for vegetationand insects were comparable to similar measurementsmade previously (but based on single samples of eachorganism) in an alpine ecosystem. Changes in Sr/Ca andBa/Ca ratios between birds and their food have notpreviously been measured, but the values we obtainedwere similar to those for herbivorous and carnivorousmammals at similar trophic levels. Our results provideevidence that supports the use of Sr/Ca ratios in thedetermination of human paleodiets and suggests thatSr/Ca ratios may also provide a useful tool in studiesof modern food webs. Furthermore, our findings suggestthat 90Sr from nuclear fallout will notbioaccumulate in forests and that changes in Sr/Caratios between trophic levels will need to beconsidered in some cases when using87Sr/86Sr as a tracer of calciumbiogeochemistry.

Notizen: Abstract The 40,000-dalton glycoprotein and 2000-dalton peptide inducing selective Ca2+-transport through bilayer lipid membranes were isolated from beef heart homogenate and mitochondria. Micromolar concentrations of these substances were found to increase the conductivity of membranes by 3–4 orders. Transmembrane Ca2+ gradient induces an electric potential difference whose magnitude is close to the theoretical for ideal Ca2+ selectivity. The inhibitor of mitochondrial Ca2+ transport, ruthenium red, abolishes both the glycoprotein-and peptide-induced Ca2+ transport in bilayer lipid membranes. Thiol groups essential for Ca2+ transport activity were revealed in the glycoprotein and peptide. Addition of these substances to rat liver mitochondria induces Ca2+-dependent inhibition of the state 3 respiration that can be released by uncouplers (oligomycin-like effect).