Regulation of the mitochondrial proton gradient by cytosolic Ca2+ signals

Mitochondria convert the energy stored in carbohydrate and fat into ATP molecules that power enzymatic reactions within cells, and this process influences cellular calcium signals in several ways. By providing ATP to calcium pumps at the plasma and intracellular membranes, mitochondria power the calcium gradients that drive the release of Ca2+ from stores and the entry of Ca2+ across plasma membrane channels. By taking up and subsequently releasing calcium ions, mitochondria determine the spatiotemporal profile of cellular Ca2+ signals and the activity of Ca2+-regulated proteins, including Ca2+ entry channels that are themselves part of the Ca2+ circuitry. Ca2+ elevations in the mitochondrial matrix, in turn, activate Ca2+-dependent enzymes that boost the respiratory chain, increasing the ability of mitochondria to buffer calcium ions. Mitochondria are able to encode and decode Ca2+ signals because the respiratory chain generates an electrochemical gradient for protons across the inner mitochondrial membrane. This proton motive force (Δp) drives the activity of the ATP synthase and has both an electrical component, the mitochondrial membrane potential (ΔΨ m ), and a chemical component, the mitochondrial proton gradient (ΔpH m ). ΔΨ m contributes about 190mV to Δp and drives the entry of Ca2+ across a recently identified Ca2+-selective channel known as the mitochondrial Ca2+ uniporter. ΔpH m contributes ~30mV to Δp and is usually ignored or considered a minor component of mitochondria respiratory state. However, the mitochondrial proton gradient is an essential component of the chemiosmotic theory formulated by Peter Mitchell in 1961 as ΔpH m sustains the entry of substrates and metabolites required for the activity of the respiratory chain and drives the activity of electroneutral ion exchangers that allow mitochondria to maintain their osmolarity and volume. In this review, we summarize the mechanisms that regulate the mitochondrial proton gradient and discuss how thermodynamic concepts derived from measurements in purified mitochondria can be reconciled with our recent findings that mitochondria have high proton permeability in situ and that ΔpH m decreases during mitochondrial Ca2+ elevation

A study of the supervisory process, as a contribution to the in-service education of the nurses

Thesis (M.S.)--Boston Universit

RB501, RB502, RB503, RB504 and RB505 antibodies recognize the human UNC93B1 protein by ELISA

The recombinant antibodies RB501, RB502, RB503, RB504 and RB505 detect by ELISA the human Protein unc-93 homolog B1fused to a GST protein

Passivating contacts for homojunction solar cells using a-Si:H/c-Si hetero-interfaces

Crystalline silicon (c-Si) homojunction solar cells account for over 90% of the current photovoltaic market. However, further progress of this technology is limited by recombinative losses occurring at their metal-semiconductor contacts. The goal of this thesis is to develop passivating contacts to resolve this issue. The novel idea presented in this work is to insert an ultra-thin wide bandgap semiconductor-hydrogenated amorphous silicon (a-Si:H)-film underneath the metal to passivate the doped c-Si surface and suppress the recombination of minority charge carriers. Simultaneously, this layer should provide a contact to the metal allowing majority charge carrier transport. A transparent conductive oxide is additionally inserted between the a-Si:H layer and the metal to ensure efficient carrier collection. This concept is inspired by the silicon heterojunction solar cells, a technology characterized by extremely high open-circuit voltages. The development of these new passivating contacts requires two features: a homojunction, for charge separation, and a silicon heterojunction contact for improved passivation. In this thesis, we explicitly focus on large-area thin-film deposition technology for fabrication of our devices, guaranteeing the scalability of our findings. The main results of this thesis are then threefold. First, we show that, using low-temperature plasma enhanced chemical vapor deposition, a doped homo-epitaxial layer can be deposited to form the homojunction. Second, we develop passivating contacts and optimize them in silicon heterojunction solar cells. An in-depth analysis of the contact formation is provided, including a detailed investigation of the relevant interfaces in our proposed structure. Finally, combining these two technologies, we demonstrate a proof-of-concept for these passivating contacts. Highly doped phosphorus- and boron-doped c-Si surfaces are shown to be efficiently passivated by a-Si:H layers and a lower contact resistivity is obtained for our optimized passivating contacts on such doped surfaces compared to a heterojunction contact on lightly doped surfaces. We show that homojunction solar cells on diffused and ion-implanted wafers featuring such passivating contacts (called homo-hetero cells hereinafter) yield improved open-circuit voltages compared to conventional homojunction solar cells, due to reduction of recombination losses. Additionally, the temperature coefficient of such homo-hetero solar cells is lower. With these advantages, the homo-hetero solar cells outperform homojunction solar cells when operating at a cell temperature above 60 °C. This work contributes to the research and development of high-efficiency silicon solar cells by providing new insights on the properties of contact formation and a novel contact-type

?2-Microglobulin Amyloid Fibril-Induced Membrane Disruption Is Enhanced by Endosomal Lipids and Acidic pH

Although the molecular mechanisms underlying the pathology of amyloidoses are not well understood, the interaction between amyloid proteins and cell membranes is thought to play a role in several amyloid diseases. Amyloid fibrils of ?2-microglobulin (?2m), associated with dialysis-related amyloidosis (DRA), have been shown to cause disruption of anionic lipid bilayers in vitro. However, the effect of lipid composition and the chemical environment in which ?2m-lipid interactions occur have not been investigated previously. Here we examine membrane damage resulting from the interaction of ?2m monomers and fibrils with lipid bilayers. Using dye release, tryptophan fluorescence quenching and fluorescence confocal microscopy assays we investigate the effect of anionic lipid composition and pH on the susceptibility of liposomes to fibril-induced membrane damage. We show that ?2m fibril-induced membrane disruption is modulated by anionic lipid composition and is enhanced by acidic pH. Most strikingly, the greatest degree of membrane disruption is observed for liposomes containing bis(monoacylglycero)phosphate (BMP) at acidic pH, conditions likely to reflect those encountered in the endocytic pathway. The results suggest that the interaction between ?2m fibrils and membranes of endosomal origin may play a role in the molecular mechanism of ?2m amyloid-associated osteoarticular tissue destruction in DRA

Interactions between Electron and Proton Currents in Excised Patches from Human Eosinophils

The NADPH–oxidase is a plasma membrane enzyme complex that enables phagocytes to generate superoxide in order to kill invading pathogens, a critical step in the host defense against infections. The oxidase transfers electrons from cytosolic NADPH to extracellular oxygen, a process that requires concomitant H+ extrusion through depolarization-activated H+ channels. Whether H+ fluxes are mediated by the oxidase itself is controversial, but there is a general agreement that the oxidase and H+ channel are intimately connected. Oxidase activation evokes profound changes in whole-cell H+ current (IH), causing an approximately −40-mV shift in the activation threshold that leads to the appearance of inward IH. To further explore the relationship between the oxidase and proton channel, we performed voltage-clamp experiments on inside-out patches from both resting and phorbol-12-myristate-13-acetate (PMA)-activated human eosinophils. Proton currents from resting cells displayed slow voltage-dependent activation, long-term stability, and were blocked by micromolar internal [Zn2+]. IH from PMA-treated cells activated faster and at lower voltages, enabling sustained H+ influx, but ran down within minutes, regaining the current properties of nonactivated cells. Bath application of NADPH to patches excised from PMA-treated cells evoked electron currents (Ie), which also ran down within minutes and were blocked by diphenylene iodonium (DPI). Run-down of both IH and Ie was delayed, and sometimes prevented, by cytosolic ATP and GTP-γ-S. A good correlation was observed between the amplitude of Ie and both inward and outward IH when a stable driving force for e− was imposed. Combined application of NADPH and DPI reduced the inward IH amplitude, even in the absence of concomitant oxidase activity. The strict correlation between Ie and IH amplitudes and the sensitivity of IH to oxidase-specific agents suggest that the proton channel is either part of the oxidase complex or linked by a membrane-limited mediator