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Introdução: Nos últimos anos, a Doença Renal Crônica tem sido considerada um grave problema de saúde pública. Isso se deve principalmente à elevada mortalidade anual, devido a distúrbios cardiovasculares. Alguns dos principais responsáveis pela mortalidade dessa população são as doenças cardíacas e dentro delas os episódios arrítmicos. Diante dessa perspectiva, o presente estudo objetivou investigar a prevalência de arritmias ventriculares e supraventriculares em pacientes portadores de doença renal crônica dialítica. Método: Trata-se de um estudo de coorte prospectivo, no qual foi avaliada a presença de arritmias cardíacas e risco de morte súbita cardíaca em 35 pacientes do Real Hospital Português de Pernambuco. Resultados: Foi observado que 71,4% dos pacientes são do sexo masculino, 85,7% não é de cor negra e 57,1% possui idade acima de 50 anos. Pacientes com níveis plasmáticos inadequados de potássio, cálcio e aqueles que não utilizavam medicamentos, apresentaram maior prevalência de arritmias ventriculares e supraventriculares. Discussão: Alterações dos níveis normais de cálcio e potássio geram intercorrências cardiovasculares, principalmente, arritmias. Maior prevalência de arritmias em indivíduos sem uso de medicamentos pode estar relacionado pelo fato de muitos pacientes serem subdiagnosticados. Além disso, houve maior prevalência de arritmia ventricular durante a hemodiálise, quando comparada à arritmia supraventricular. A idade mostrou-se um importante fator relacionado às arritmias em pacientes dialíticos. Conclusão: Constata-se que pacientes renais crônicos dialíticos apresentam alterações dos níveis normais de eletrólitos e hipertensão arterial que aumentam a ocorrência de arritmias cardíacas, principalmente ventriculares, aumentando o risco de morte súbita nessa população.

To investigate the effects of tamoxifen on Staphylococcus aureus α-hemolysin channel (α-HL) in planar lipid bilayers with electrophysiological characterization and docking studies. Planar lipid bilayer membranes were prepared and α-HL (0.07 mg/mL) was added to the standard solution in cis compartment of the experimental chamber. All experiments were performed at room temperature using an Axopatch 200A amplifier in the voltage clamp mode. At pH 7.5, α-HL channels were usually in a high conductance ~4 nS and rarely switch to low conductance states. After the ion channel was incorporated in bilayer membrane, the tamoxifen was also added to the standard solution to the cis compartment. To docking studies, atomics coordinates for the α-HL heptameric channel was retrieved from PDB ID (7AHL) and the structure of tamoxifen was removed from the Pubchem, their coordinates were built and minimized with Avogadro software. The molecular docking experiments were performed using the Dockthor online portal. The tamoxifen inhibited (P < 0.05) α-HL channel conductance and it was a voltage-dependent manner. The three best docking solutions and the α-HL channel were evaluated, it was observed the connection mode with the highest affinity of interaction has a greater number of types of polar interaction. The residues present interactions of greater energy were 111 and 147 that form the remainders of the constriction in the channel of α-HL. The other conformers were accommodated in a region with more hydrophobic characteristics (valine 149). The mechanism of Staphylococcus aureus α-hemolysin inhibition by tamoxifen was blockade over the constriction of channel. Investigar los efectos del tamoxifeno sobre el canal de α-hemolisina obtenido de Staphylococcus aureus (α-HL) en bicapas lipídicas planas con caracterización electrofisiológica y estudios de acoplamiento. Se prepararon membranas planas y se añadió α-HL (0,07mg/ml) a la solución estándar en la cámara cis de la cámara experimental. Todos los experimentos se llevaron a cabo a temperatura ambiente usando un amplificador Axopatch 200A en el modo de "sujeción de voltaje". A pH 7,5, los canales de α-HL estaban generalmente en alta conductancia ~4nS y rara vez cambian a estados de baja conductancia. Después de que el canal de iones se incorporó a la membrana, también se añadió tamoxifeno a la solución estándar en el compartimento cis. Para los estudios de acoplamiento, las coordenadas atómicas del canal heptamérico se obtuvieron del PDBID (7AHL) y la estructura del tamoxifeno de Pubchem, sus coordenadas se construyeron y minimizaron con el programa Avogadro. Los experimentos de acoplamiento molecular se llevaron a cabo utilizando el portal en línea Dockthor. El tamoxifeno inhibió (P

Microcystins (MCs) are a class of cyclic heptapeptides with more than 100 variants produced by cyanobacteria present in surface waters. MCs are potent hepatotoxic agents responsible for fatal poisoning in animals and humans. Several techniques are employed in the detection of MCs, however, there is a shortage of methods capable of discriminating variants of MCs. In this work we demonstrate that the α-hemolysin (αHL) nanopore can detect and discriminate the variants (LR, YR and RR) of MCs in aqueous solution. The discrimination process is based on the analysis of the residence times of each variant of MCs within the unitary nanopore, as well as, on the amplitudes of the blockages in the ionic current flowing through it. Simulations of molecular dynamics and calculation of the electrostatic potential revealed that the variants of MCs present different charge distribution and correlated with the three patterns on the amplitudes of the blockages in the ionic current. Additionally, molecular docking analysis indicates different patterns of interaction of the variants of MCs with two specific regions of the nanopore. We conclude that αHL nanopore can discriminate variants of microcystins by a mechanism based mainly on electrostatic interaction. Finally, we propose the use of nanopore-based technology as a promising method for analyzing microcystins in aqueous solutions.

Nanopores have emerged as molecule detectors and more studies are necessary to clarify the analyte–nanopore interaction. Here, we report the influence of cations of the Hofmeister series on a simple bimolecular complexation reaction between poly(ethyleneglycol) (PEG) and α-hemolysin (αHL) nanopore at the single-molecule level. The kinetic constants (on-rate and off-rate) of interaction of PEG molecules with αHL nanopore depend strongly on the type of cation. In the case of on-rate constant, the difference reaches several dozen times. As a consequence of this, both transition rate and detection limit of the nanopore-based sensor were changed. An inverse relationship was demonstrated for the off-rate constant and the solubility of PEG. Except lithium, the other alkali metal cations significantly affect the interaction of PEG with the nanopore and, similarly to potassium, they also bind to this polymer. Thus, the PEG/αHL nanopore interaction can be strongly influenced by the type of cation. The cation-induced specific effect on polymer detection with a single αHL nanopore appears to occur by competition of the cation and PEG by water. Finally, our results represent a guide to select the appropriate physicochemical conditions that enhance the analyte–nanopore interaction, thereby improving the sensitivity of nanopore-based sensors.

Studies employing a single protein nanopore as a molecular recognition element in the development of analytical devices - biosensors, spectrometers, DNA sequencing - have increased considerably in the last decade. Several studies show the potential of these bionanostructures for future stochastic biosensing technology. Stochastic biosensing is an approach that relies on the observation of individual binding events between analyte molecules and a single receptor. This approach is inherent to the organisms that use a single protein nanopore as a key element to start, manage and maintain the chemical and biophysical processes of living cells. Here, we discuss alpha-toxin as a bacterial exotoxin and prototype of a protein nanopore in real-time detection and characterization of molecules in aqueous systems.

Despite extensive research in the nanopore-sensing field, there is a paucity of experimental studies that investigate specific ion effects in confined spaces, such as in nanopores. Here, the effect of halogen anions on a simple bimolecular complexation reaction between monodisperse poly(ethylene glycol) (PEG) and α-hemolysin nanoscale pores have been investigated at the single-molecule level. The anions track the Hofmeister ranking according to their influence upon the on-rate constant. An inverse relationship was demonstrated for the off-rate and the solubility of PEG. The difference among anions spans several hundredfold. Halogen anions play a very significant role in the interaction of PEG with nanopores although, unlike K+, they do not bind to PEG. The specific effect appears dominated by a hydration-dehydration process where ions and PEG compete for water. Our findings provide what we believe to be novel insights into physicochemical mechanisms involved in single-molecule interactions with nanopores and are clearly relevant to more complicated chemical and biological processes involving a transient association of two or more molecules (e.g., reception, signal transduction, enzyme catalysis). It is anticipated that these findings will advance the development of devices with nanopore-based sensors for chemical and biological applications.

Nanopores have emerged in recent years as versatile single molecule detectors. The sensing principle is based on transient interruptions in the ion-current of an electrolyte, induced by the entry, transport, and exit of a particular analyte from the pore. The improving the detection capability of the nanopore is essential. Recently (Rodrigues et al., 2008) we have shown that the “salting out” are responsible for the KCl-induced enhancement in identification of individual molecules of poly(ethylene glycol) using solitary α-hemolysin nanoscale pores. The result suggested that specific ion effects may take place. Hofmeister effects are almost ubiquitous (Lo Nostro et al., 2006). Despite the huge number of studies devoted to this issue that date back more than a century, their origin is still debated. There are only isolated studies of the phenomenon at the confined spaces. For this reason, we focused on the effect of monovalent anions on a simple bimolecular complexation reaction between poly(ethylene glycol) and α-hemolysin nanoscale pore at the single-molecule level.We find that the type of anions used here has dramatic influence on the “on-rate” constant of the reaction (the difference reaches several hundred times). As a consequence of this, the transition rate and the detection limit of the nanopore based sensor is correspondingly changed. The all probed anions follow the Hofmeister ranking according to their influence on the on-rate constant (F- > Cl- > Br- > I- ) and the solubility of the analyte (F- < Cl- < Br- < I- ). Therefore, salting-out phenomenon is responsible for the anion-induced effect on single molecule detection with a solitary protein nanopore. These results will advance the development of devices with sensor elements based on single nanopores.Supported by CNPq, RENAMI and InstINAMI, Brazil.