Kinetic Process of an Alkaline Earth Metal Ion Transmembrane through ZIF-8.

The confinement effect of biological ion channels regulates the transport of molecules and ions due to angstrom-sized pores. The structure of the potassium channel has a selection region (3-4 Å), a cavity (10 Å), and a gated region, while ZIF-8 has intrinsic pores with a 3.4 Å aperture and an 11.6 Å cavity similar to those of the potassium channel. Inspired by this, we constructed the glass/ZIF-8 hybrid membrane through an electrochemical growth process to explore the kinetics of the ion transmembrane by I-V curves and electrochemical impedance spectroscopy. These complementary approaches yield highly correlated results that show that ion transportation of the ZIF-8 membrane follows Arrhenius behavior. The rates of ions are controlled by the transmembrane activation energy, in which the ionic charge and radius play an important role.

Utilización de hidrolasas en la preparación de fármacos e intermedios homoquirales / Hydrolases use in the preparation of drugs and homochiral intermediates

La exquisita regio y estereoselectividad que presentan los biocatalizadores,amén de la buena sostenibilidad inherente a su empleo,permiten la realización de protocolos sintéticos difícilmente alcanzablespor las metodologías clásicas, a menos que se lleven a cabocostosos procesos de protección y desprotección. En este trabajo serevisan algunos ejemplos en los cuales las hidrolasas (las enzimas másempleadas dentro del ámbito de las Biotransformaciones) están implicadascomo biocatalizadores para la obtención del eutómero (esteroisómeroactivo, que presenta la actividad terapéutica deseada) biende diferentes fármacos quirales, o bien de precursores a través de loscuales se puedan sintetizar. Así, se comentarán distintos tipos de biotransformacionespara la obtención de compuestos con diferentesactividades: antivirales, anticancerosos, antihipertensivos, antiinflamatorios,etc, haciendo hincapié en la versatilidad y comodidad delempleo de los biocatalizadores en los pasos sintéticos descritos(AU)

The excellent regio and steroselectivity of biocatalysts, combinedwith their environmental friendly behaviour, make possible to carryout under biocatalytical conditions many processes which, conductedon strictly classical methodologies, would demand expensive andtedious protection and de-protection steps. In this work we reviewsome examples in which hydrolases (the most useful enzymes in theBiotransformations field) catalyse different reactions for synthesizingonly the therapeutically essential stereoisomer of differenthomochiral building blocks for drugs. Thus, processes leading toantiviral, anticancer, antihypertensive or antiinflammatory drugs,along with many others, are described, remarking the versatility andutility of the biocatalysts in the above-mentioned processes(AU)

Avaliação de ionóforos pela técnica da perda do potássio celular e produção de gases in vitro / Ionophores evaluation by intracellular potassium depletion and in vitro gas production

Dois estudos foram realizados com vacas lactantes utilizadas como unidade experimental e doadoras de líquido ruminal, sendo as populações de bactérias utilizadas para avaliar a ação de níveis crescentes de lasalocida e monensina na resistência à perda de potássio intracelular, e para produção de gases in vitro. A perda de potássio (Kmax) da lasalocida foi menor para a população de bactérias obtidas do líquido de rúmen de vacas submetidas a dietas com monensina, óleo de soja e monensina mais óleo de soja (19,4 a 25,4 por cento) quando comparada com a perda de potássio em vacas submetidas a dietas sem ionóforo e óleo de soja (30,1 por cento). O mesmo ocorreu para a perda de potássio da monensina, em que o menor valor foi de 6,5 por cento para monensina mais óleo e o maior, de 29,5 por cento, para o controle. Necessita-se de alta concentração de monensina (Kd= 2,3µM), porém baixa de lasalocida (Kd= 0,2µM) para causar a metade da perda máxima de potássio intracelular da população de bactérias do rúmen de vacas submetidas a dietas com monensina. As populações de bactérias de vacas submetidas às dietas com monensina foram sensíveis à lasalocida. As amostras incubadas com própolis produziram menor volume de gases (12,9ml/100g de MS)

Two studies were carried out with lactating cows as experimental units and ruminal fluid donors. The ruminal bacteria population was used to evaluate the action of increasing levels of lasalocid and monensin on resistance of intracellular potassium depletion and in vitro gas production intracellular depletion potassium (Kmax) of lasalocid was lower to ruminal bacteria population obtained from rumen of cows fed diets with monensin, soybean oil and monensin plus soybean oil (19.4 to 25.4 percent) when compared to cows fed with control diet (30.1 percent). The same occurred for intracellular depletion potassium (Kmax) of monensin, in which the lowest value was 6.5 percent to monensin plus soybean oil and the greatest was 29.5 percent to control. High monensin concentration (Kd= 2.3µM) and low lasalocid concentration (Kd= 0.2µM) were necessary to cause half of maximum potassium depletion in ruminal bacteria population from cows fed diet with monensin. The ruminal bacteria population from cows feed diet with monensin were sensible to lasalocid. In vitro gas production showed the lowest volume when diets were incubated with propolis (12,9ml/100g of DM)

K+ channels involved in contractility of rabbit small intestine

Most excitable cells, including gastrointestinal smooth muscle cells, express several types of K+channels. The aim of this study was to examine the types of K+ channels involved in the contractility of longitudinal smooth muscle of rabbit small intestinein vitro. Spontaneous contractions and KCl-stimulated contractions were reduced by atropine, phentolamine, propranolol, suramin, tetrodotoxin and indomethacin. The amplitude and tone of spontaneous contractions were increased by apamin, charybdotoxin, iberiotoxin, E4031, tetraetylammonium (TEA) and BaCl2. The frequency of contractions was reduced in the presence of apamin and TEA and increased by charybdotoxin. It was found that 4-aminopyridine increased the tone of spontaneous contractions and reduced the amplitude and frequency of contractions. Glibenclamide did not modify the amplitude, frequency or tone of contractions. KCl-stimulated contractions were increased by E4031, were not modified by apamin, glibenclamide, NS1619 or diazoxide, and were reduced by charybdotoxin, TEA, 4-aminopyridine or BaCl2. These results suggest that both Ca2+-activated K+ channels of small and high conductance, and HERG K+ channels and inward rectifier K+ channels participate in spontaneous contractions of small intestine. On the other hand, voltage-dependent K+ channels, HERG K+ channels, inward rectifier K+ channels and high conductance Ca2+-activated K+ channels are involved in KCl-stimulated contractions (AU)

La mayoría de las células excitables, incluyendo las células lisas gastrointestinales, expresan varios tipos de canales de K+. El objetivo de este estudio es examinar los tipos de canales de K+que están involucrados en la contractilidad del músculo liso longitudinal del intestino delgado de conejoin vitro. Las contracciones espontáneas y las producidas por KCl se redujeron por atropina, fentolamina, propranolol, suramina, tetrodotoxina e indometacina. La amplitud y tono de las contracciones espontáneas aumentaron por apamin, charybdotoxina, iberiotoxina, E4031, tetraetilamonio (TEA) y BaCl2, mientras que la frecuencia de las contracciones se redujo en presencia de apamin, charybdotoxina y TEA. La 4-aminopiridina aumentó el tono de las contracciones espontáneas y redujo la amplitud y frecuencia de las contracciones. La glibenclamida no modificó la amplitud, frecuencia y tono de las contracciones. Las contracciones producidas por el KCl aumentaron en presencia de E4031, no fueron modificadas por el apamin, glibenclamida, NS1619 o diazóxida y disminuyeron en presencia de la charybdotoxina, TEA, 4-aminopiridina o BaCl2. Estos resultados sugieren que los canales de K+ activados por Ca2+ de pequeña y gran conductancia, canales de K+ HERG canales de K+ rectificadores de entrada participan en las contracciones espontáneas del intestino delgado. Por otra parte, los canales de K+ voltaje-dependientes, canales de K+ HERG, canales de K+ rectificadores de entrada y canales de K+activados por Ca2+ de gran conductancia están implicados en las contracciones producidas por el KCl (AU)

Disruption of cell volume regulation by mercuric chloride is mediated by an increase in sodium permeability and inhibition of an osmolyte channel in skate hepatocytes.

The mechanism by which mercury leads to cell swelling and impairs the normal regulatory volume decrease (RVD) in cells swollen in hypotonic media was examined in hepatocytes isolated from the little skate, Raja erinacea, an osmoconforming marine elasmobranch. Skate hepatocytes treated with 50 microM HgCl2 in isotonic medium swelled to volumes double those of control cells, and this was associated with an increase in Na+ and K+ permeability. The gain in intracellular Na+ exceeded the K+ loss by 0.27 microEq/mg protein, accounting in large part for the observed cell swelling. The effects of mercury were blunted when hepatocytes were incubated in medium in which the Na+ was replaced with K+, and were essentially absent when Na+ was replaced with choline+, indicating an important role of Na+ influx in mediating mercury's effects on cell volume regulation. The inhibition of RVD by mercury was prevented if the metal was administered as a mercaptide with dithiothreitol or glutathione. However, when these chelating agents were added after the mercury, only the membrane permeant dithiothreitol was able to reverse the inhibition of RVD, suggesting an intracellular site of action. Mercuric chloride also produced a concentration-dependent inhibition of the ATP-sensitive volume-regulatory osmolyte channel in skate hepatocytes, as assessed by inhibition of swelling-activated [14C]taurine efflux. [14C]Taurine efflux was inhibited at mercury concentrations (20-40 microM) that had no effect on intracellular ATP levels or ATP/ADP ratios, consistent with a direct interaction with the channel. These findings indicate that mercury impairs cell volume regulation in skate hepatocytes at multiple sites, including the volume-regulatory osmolyte channels, and Na+ and K+ permeability pathways. The combined effects of increased Na+ influx and the inability to extrude organic osmolytes may account for the inhibition of RVD.

An analysis of the Maxi-K+ (KCa) channel in cultured human corporal smooth muscle cells.

Previous studies have demonstrated that cultured corporal smooth muscle cells have prominent outward K currents composed of several different K channel subtypes. The goals of the present investigation were (1) to assert the nature of these channels and to evaluate the characteristics of the most predominant of these channel subtypes, the Maxi-K+ (KCa) channel, and (2) to compare KCa channel behavior in cultured corporal smooth muscle cells derived from the human corpus cavernosum of two distinct patient populations. The patient population was subdivided into two broad diagnostic categories: Group 1: 4 patients without evidence of organic disease of the corpus cavernosum, 3 of whom had documented erections; and Group 2: 4 patients with organic erectile dysfunction. Consistent with previous observations, 3 different K channel subtypes were detected in both patient populations, with corresponding conductances of 180, 100 and 40 pS, respectively. The approximately 183 pS channel was identified as the KCa channel based on its selective permeability to K+ and the fact that its open probability was modulated by both membrane potential and intracellular calcium levels. Specifically, the relative permeability of the 183 pS KCa channel to K+, Rb+, and NH4+ was 1.00:0.64:0.46. The channel was virtually impermeable to Na+ and Li+ (relative permeability < 0.02). In addition, the KCa channel was responsible for more than 90% of the outward K+ current passed through the cell membrane when depolarized. Furthermore, pharmacological studies using the K channel blocker tetraethylammonium ion (TEA) revealed that the sensitivity of KCa channels to TEA inhibition (as judged by the [TEA] required to block one-half of the outward whole cell current induced by a 90 mV depolarizing pulse) in cells from Group 1 patients was 1.05 +/- 0.22 mM. (n = 10 cells), while in sharp contrast the observed value for cells from Group 2 patients was 12.7 +/- 3.8 (n = 9 cells). The difference between the two groups was highly significant. These observations confirm and extend our previous studies to suggest that the KCa channel plays an important role in corporal smooth muscle physiology and, moreover, that alterations in the function/regulation of KCa channels may be an important feature of organic erectile dysfunction. As such, altered KCa channel behavior may contribute to an impaired hyperpolarizing ability of corporal smooth muscle, possibly altering intracellular calcium homeostasis and, perhaps, corporal smooth muscle reactivity and tone.