RESUMO
The crystalline structures of the superionic high-temperature copper selenides Cu(2-x)Se (0 < x < 0.25) produced using mechanical alloying were investigated using X-ray diffraction (XRD). The measured XRD patterns showed the presence of peaks corresponding to the crystalline superionic high-temperature alpha-Cu(2)Se phase in the as-milled sample, and its structural data were determined by means of a Rietveld refinement procedure. After heat treatment in argon at 473 K for 90 h, this phase transforms to the superionic high-temperature alpha-Cu(1.8)Se phase, whose structural data were also determined by Rietveld refinement. In this phase, a very low occupation of the trigonal 32(f) sites ( approximately 3%) by Cu ions is found. In order to explain the evolution of the phases in the samples, two possible mechanisms are suggested: (i). the high mobility of Cu ions in superionic phases and (ii). the important diffusive processes in the interfacial component of samples produced by mechanical alloying.
Assuntos
Ligas/química , Cobre/química , Selênio/química , Ligas/síntese química , Temperatura Alta , Conformação Molecular , Difração de Pó , Difração de Raios XRESUMO
A comparison of the release of endogenous and of tritiated acetylcholine (3H-ACh) was performed in eserinized slices of rat cerebral cortex labelled in vitro in the presence of 0.43 microM tityustoxin (TsTX), a scorpion venom known to increase the overflow of endogenous acetylcholine. The endogenous and the radioactive ACh were spontaneously released into the organ bath. At the moment when the spontaneous efflux had levelled off, the endogenous ACh collected during 1 min accounted for 1.03 +/- 0.14% of the tissue content and a similar value (0.80 +/- 0.26%) was found for 3H-ACh. The basal outflow as well as the tissue retention of ACh and of 3H-ACh were not modified by exposure to the scorpion venom. In the presence of 20 mM KCl for 1 min, the overflow of both radioactive and endogenous ACh was increased up to approximately 100% above basal levels and this K+-evoked release was almost doubled under the action of TsTX. The results presented are compatible with the view that no major functional differences exist in the rat cortex between responses of pools storing 3H-ACh synthesized from 3H-choline and those storing ACh formed from endogenous substrate.
Assuntos
Acetilcolina/metabolismo , Córtex Cerebral/metabolismo , Venenos de Escorpião/farmacologia , Animais , Colina/metabolismo , Técnicas In Vitro , Masculino , Ratos , Ratos Endogâmicos , TrítioRESUMO
A comparison of the release of endogenous and of tritiated acetylcholine (3H-ACh) was performed in eserinized slices of rat cerebral cortex labelled in vitro in the presence of 0.43 microM tityustoxin (TsTX), a scorpion venom known to increase the overflow of endogenous acetylcholine. The endogenous and the radioactive ACh were spontaneously released into the organ bath. At the moment when the spontaneous efflux had levelled off, the endogenous ACh collected during 1 min accounted for 1.03 +/- 0.14
of the tissue content and a similar value (0.80 +/- 0.26
) was found for 3H-ACh. The basal outflow as well as the tissue retention of ACh and of 3H-ACh were not modified by exposure to the scorpion venom. In the presence of 20 mM KCl for 1 min, the overflow of both radioactive and endogenous ACh was increased up to approximately 100
above basal levels and this K+-evoked release was almost doubled under the action of TsTX. The results presented are compatible with the view that no major functional differences exist in the rat cortex between responses of pools storing 3H-ACh synthesized from 3H-choline and those storing ACh formed from endogenous substrate.
RESUMO
A comparison of the release of endogenous and of tritiated acetylcholine (3H-ACh) was performed in eserinized slices of rat cerebral cortex labelled in vitro in the presence of 0.43 microM tityustoxin (TsTX), a scorpion venom known to increase the overflow of endogenous acetylcholine. The endogenous and the radioactive ACh were spontaneously released into the organ bath. At the moment when the spontaneous efflux had levelled off, the endogenous ACh collected during 1 min accounted for 1.03 +/- 0.14
of the tissue content and a similar value (0.80 +/- 0.26
) was found for 3H-ACh. The basal outflow as well as the tissue retention of ACh and of 3H-ACh were not modified by exposure to the scorpion venom. In the presence of 20 mM KCl for 1 min, the overflow of both radioactive and endogenous ACh was increased up to approximately 100
above basal levels and this K+-evoked release was almost doubled under the action of TsTX. The results presented are compatible with the view that no major functional differences exist in the rat cortex between responses of pools storing 3H-ACh synthesized from 3H-choline and those storing ACh formed from endogenous substrate.