RESUMEN
The mitochondrial network of cardiac cells is finely tuned for ATP delivery to sites of energy demand; however, emergent phenomena, such as mitochondrial transmembrane potential oscillations or propagating waves of depolarization have been observed under metabolic stress. While regenerative signaling by reactive oxygen species (ROS)-induced ROS release (RIRR) has been suggested as a potential trigger, it is unknown how it could lead to widespread responses. Here, we present a novel computational model of RIRR transmission that explains the mechanisms of this phenomenon. The results reveal that superoxide mediates neighbor-neighbor activation of energy-dissipating ion channels, while hydrogen peroxide distributes oxidative stress to sensitize the network to mitochondrial criticality. The findings demonstrate the feasibility of RIRR as a synchronizing factor across the dimensions of the adult heart cell and illustrate how a cascade of failures at the organellar level can scale to impact cell and organ level functions of the heart.
Asunto(s)
Peróxido de Hidrógeno/metabolismo , Mitocondrias/metabolismo , Modelos Biológicos , Difusión , Potencial de la Membrana Mitocondrial , Estrés OxidativoRESUMEN
BACKGROUND: Sudden cardiac death often involves arrhythmias triggered by metabolic stress. Loss of mitochondrial function is thought to contribute to the arrhythmogenic substrate, but how mitochondria contribute to uncoordinated electrical activity is poorly understood. It has been proposed that the formation of metabolic current sinks, caused by the nonuniform collapse of mitochondrial inner membrane potential (ΔΨm), contributes to re-entrant arrhythmias because ΔΨm depolarization is tightly coupled to the activation of sarcolemmal ATP-sensitive K(+) channels, hastening action potential repolarization and shortening the refractory period. METHODS AND RESULTS: Here, we use computational and experimental methods to investigate how ΔΨm instability can induce re-entrant arrhythmias. We develop the first tissue-level model of cardiac electrical propagation incorporating cellular electrophysiology, excitation-contraction coupling, mitochondrial energetics, and reactive oxygen species balance. Simulations show that re-entry and fibrillation can be initiated by regional ΔΨm loss because of the disparity of refractory periods inside and outside the metabolic sink. Computational results are compared with the effects of a metabolic sink generated experimentally by local perfusion of a mitochondrial uncoupler in a monolayer of cardiac myocytes. CONCLUSIONS: The results demonstrate that regional mitochondrial depolarization triggered by oxidative stress activates sarcolemmal ATP-sensitive K(+) currents to form a metabolic sink. Consequent shortening of the action potential inside, but not outside, the sink increases the propensity for re-entry. ΔΨm recovery during pacing can lead to novel mechanisms of ectopic activation. The findings highlight the importance of mitochondria as potential therapeutic targets for sudden death associated with cardiovascular disease.
Asunto(s)
Arritmias Cardíacas/etiología , Sistema de Conducción Cardíaco/metabolismo , Mitocondrias Cardíacas/metabolismo , Miocitos Cardíacos/metabolismo , Estrés Oxidativo , Potenciales de Acción , Animales , Arritmias Cardíacas/metabolismo , Arritmias Cardíacas/fisiopatología , Simulación por Computador , Muerte Súbita Cardíaca/etiología , Acoplamiento Excitación-Contracción , Cobayas , Sistema de Conducción Cardíaco/fisiopatología , Humanos , Canales KATP/metabolismo , Potencial de la Membrana Mitocondrial , Modelos Cardiovasculares , Análisis Numérico Asistido por Computador , Ratas , Ratas Sprague-Dawley , Especies Reactivas de Oxígeno/metabolismo , Periodo Refractario Electrofisiológico , Sarcolema/metabolismo , Factores de TiempoRESUMEN
This article describes the utilization of laminar microflows for time-resolved emission measurements with steady-state excitation and detection. Passing a laminar flow through a short illuminated section of a microchannel provided a means for pulsed-like photoexcitation of the moieties carried by the fluid. Imaging the microchannel flows carrying thus photoexcited chelates of lanthanide ions allowed us to extract their excited-state lifetimes from the spatial distribution of the changes in the emission intensity. The lifetime values obtained using this space-domain approach agreed well with the lifetimes from time-domain measurements. This validated space-domain microfluidic approach reveals a means for miniaturization of time-resolved emission spectroscopy.
Asunto(s)
Quelantes/química , Europio/química , Técnicas Analíticas Microfluídicas , Ácidos Picolínicos/química , Terbio/química , Quelantes/síntesis química , Técnicas Analíticas Microfluídicas/instrumentación , Microscopía Fluorescente , Factores de TiempoRESUMEN
Electrostatic properties of proteins are crucial for their functionality. Carboxyamides are small polar groups that, as peptide bonds, are principal structural components of proteins that govern their electrostatic properties. We investigated the medium dependence of the molar polarization and of the permanent dipole moments of amides with different state of alkylation. The experimentally measured and theoretically calculated dipole moments manifested a solvent dependence that increased with the increase in the media polarity. We ascribed the observed enhancement of the amide polarization to the reaction fields in the solvated cavities. Chloroform, for example, caused about a 25% increase in the amide dipole moments determined for vacuum, as the experimental and theoretical results demonstrated. Another chlorinated solvent, 1,1,2,2-tetrachloroethane, however, caused an "abnormal" increase in the experimentally measured amide dipoles, which the theoretical approaches we used could not readily quantify. We showed and discussed alternatives for addressing such discrepancies between theory and experiment.
Asunto(s)
Amidas/química , Modelos Teóricos , Proteínas/química , Etano/análogos & derivados , Etano/química , Hidrocarburos Clorados/química , Electricidad EstáticaRESUMEN
This article reviews the development and the advances of print-and-peel (PAP) microfabrication. PAP techniques provide means for facile and expedient prototyping of microfluidic devices. Therefore, PAP has the potential for broadening the microfluidics technology by bringing it to researchers who lack regular or any accesses to specialized fabrication facilities and equipment. Microfluidics have, indeed, proven to be an indispensable toolkit for biological and biomedical research and development. Through accessibility to such methodologies for relatively fast and easy prototyping, PAP has the potential to considerably accelerate the impacts of microfluidics on the biological sciences and engineering. In summary, PAP encompasses: (1) direct printing of the masters for casting polymer device components; and (2) adding three-dimensional elements onto the masters for single-molding-step formation of channels and cavities within the bulk of the polymer slabs. Comparative discussions of the different PAP techniques, along with the current challenges and approaches for addressing them, outline the perspectives for PAP and how it can be readily adopted by a broad range of scientists and engineers.
Asunto(s)
Técnicas Analíticas Microfluídicas/métodos , Polímeros , Animales , Investigación Biomédica/métodos , HumanosRESUMEN
Advection driven mixing is essential for microfluidics and poses challenges to the design of microdevices. Force transducers or complex channel configurations provide means for, respectively, active or passive disrupting of laminar flows and for homogenizing the composing fluids. Print-and-peel (PAP) is a nonlithographic fabrication technique that involves direct printing of masters for molding polymer components of microdevices. PAP, hence, allows for facile and expedient preparation of microfluidic devices, without requiring access to specialized microfabrication facilities. We utilized PAP for fabrication of microfluidic devices capable of turning, expanding, and contracting microflows. We examined the mixing capabilities of these devices under flow conditions of small Reynolds numbers (0.2-20) and large Peclet numbers (260-26 000), under which advection is the dominant mode of mass transfer. We focused on mixing channels with arched shapes and examined the dependence of the mixing performance on the turns and the expansions along the direction of the microflows. Three-dimensional expansion and contraction, along with an increase in the modes of twisting of the laminar currents, improved the quality of mixing. The simplicity in the described fabrication of the investigated passive micromixers makes PAP an attractive alternative for expedient device prototyping.
Asunto(s)
Técnicas Analíticas Microfluídicas/instrumentación , Polímeros/química , Propiedades de SuperficieRESUMEN
Polypeptide helices possess considerable intrinsic dipole moments oriented along their axes. While for proline helices the dipoles originate solely from the ordered orientation of the amide bonds, for 3(10-) and alpha-helices the polarization resultant from the formation of hydrogen-bond network further increases the magnitude of the macromolecular dipoles. The enormous electric-field gradients, generated by the dipoles of alpha-helices (which amount to about 5 D per residue with 0.15 nm residue increments along the helix), play a crucial role in the selectivity and the transport properties of ion channels. The demonstration of dipole-induced rectification of vectorial charge transfer mediated by alpha-helices has opened a range of possibilities for applications of these macromolecules in molecular and biomolecular electronics. These biopolymers, however, possess relatively large bandgaps. As an alternative, we examined a series of synthetic macromolecules, aromatic oligo-ortho-amides, which form extended structures with amide bonds in ordered orientation, supported by a hydrogen-bond network. Unlike their biomolecular counterparts, the extended pi-conjugation of these macromolecules will produce bandgaps significantly smaller than the polypeptide bandgaps. Using ab initio density functional theory calculations, we modeled anthranilamide derivatives that are representative oligo-ortho-amide conjugates. Our calculations, indeed, showed intrinsic dipole moments oriented along the polymer axes and increasing with the increase in the length of the oligomers. Each anthranilamide residue contributed about 3 D to the vectorial macromolecular dipole. When we added electron donating (diethylamine) and electron withdrawing (nitro and trifluoromethyl) groups for n- and p-doping, respectively, we observed that: (1) proper positioning of the electron donating and withdrawing groups further polarized the aromatic residues, increasing the intrinsic dipole to about 4.5 D per residue; and (2) extension of the pi-conjugation over some of the doping groups narrowed the band gaps with as much as 1 eV. The investigated bioinspired systems offer alternatives for the development of broad range of organic electronic materials with nonlinear properties.
Asunto(s)
Biopolímeros/química , Modelos Moleculares , ortoaminobenzoatos/química , Enlace de HidrógenoRESUMEN
The estimation of the driving force for photoinduced charge-transfer processes, using the Rehm-Weller equation, requires the employment of redox and spectroscopic quantities describing the participating electron donor and acceptor. Although the spectroscopic data are usually obtained from diluted solutions, the redox potentials are most frequently obtained from electrochemical measurements conducted in concentrated electrolyte solutions. To correct for the differences in the media, in which the various types of measurements are conducted, a term, based on the Born equation for solvation energy of ions, is introduced in the Rehm-Weller equation. The Born correction term, however, requires a prior knowledge of the dielectric constants of the electrolyte solutions used for the redox measurements. Because of limited information for such dielectrics, the values for the dielectric constants of electrolyte solutions are approximated to the values of the dielectric constants of the corresponding neat solvents. We examined the validity of this approximation. Using cyclic voltammetry, we recorded the first one-electron oxidation potential of ferrocene for three different solvents in the presence of 1-500 mM supporting electrolyte. The dielectric constants for some of the electrolyte solutions were extracted from fluorescence measurements of a dimethylaminonaphthalimide chromophore that exhibits pronounced solvatochromism. The dielectric constants of the concentrated electrolyte solutions correlated well with the corresponding oxidation potentials. The dependence of the oxidation potential of ferrocene on the electrolyte concentration for different solvents revealed that the abovementioned approximation in the Born correction term indeed introduces a significant error in the estimation of the charge-transfer driving force from redox data collected using relatively nonpolar solvents.
Asunto(s)
Electrólitos/química , Compuestos Ferrosos/química , Impedancia Eléctrica , Electroquímica , Metalocenos , Cloruro de Metileno/química , Naftalimidas/química , Oxidación-Reducción , Solventes/químicaRESUMEN
Treatment with oxygen-containing plasma is an essential step for the fabrication of devices containing components of polydimethylsiloxane (PDMS). Such oxidative treatment chemically modifies the surface of PDMS allowing it to permanently adhere to glass, quartz, PDMS and other silica-based substrates. Overexposure of PDMS to oxidative gas plasma, however, compromises its adhesiveness. Therefore, regulation of the duration and the conditions of the plasma treatment is crucial for achieving sufficient surface activation without overoxidation. Using a semiquantitative ternary approach, we evaluated the quality of adhesion ( QA) between flat PDMS and glass substrates pretreated with oxygen plasma under a range of different conditions. The quality of adhesion manifested good correlation trends with the surface properties of the pretreated PDMS. Examination of the QA dependence on the treatment duration and on the pressure and the RF power of the plasma revealed a range of oxidative conditions that allowed for permanent adhesion with quantitative yields.
Asunto(s)
Dimetilpolisiloxanos/química , Oxígeno/química , Adhesividad , Vidrio , Microscopía de Fuerza Atómica , Polímeros , Presión , Dióxido de Silicio/química , Solventes , Propiedades de Superficie , Resistencia a la Tracción , Factores de TiempoRESUMEN
A facile nonlithographic method for expedient fabrication of microfluidic devices of poly(dimethylsiloxane) is described. Positive-relief masters for the molds are directly printed on smooth substrates. For the formation of connecting channels and chambers inside the polymer components of the microfluidic devices, cavity-forming elements are adhered to the surfaces of the masters. Using this nonlithographic approach, we fabricated microfluidic devices for detection of bacterial spores on the basis of enhancement of the emission of terbium (III) ions.