Differential Functional Changes in Visual Performance during Acute Exposure to Microgravity Analogue and Their Potential Links with Spaceflight-Associated Neuro-Ocular Syndrome.

Background: Spaceflight-Associated Neuro-Ocular Syndrome (SANS) is a complex pathology threatening the health of astronauts, with incompletely understood causes and no current specific functional diagnostic or screening test. We investigated the use of the differential performance of the visual system (central vs. perimacular visual function) as a candidate marker of SANS-related pathology in a ground-based microgravity analogue.

Biomaterials Adapted to Vat Photopolymerization in 3D Printing: Characteristics and Medical Applications.

Along with the rapid and extensive advancements in the 3D printing field, a diverse range of uses for 3D printing have appeared in the spectrum of medical applications. Vat photopolymerization (VPP) stands out as one of the most extensively researched methods of 3D printing, with its main advantages being a high printing speed and the ability to produce high-resolution structures. A major challenge in using VPP 3D-printed materials in medicine is the general incompatibility of standard VPP resin mixtures with the requirements of biocompatibility and biofunctionality.

Prokaryotic Na/H Exchangers-Transport Mechanism and Essential Residues.

Na/H exchangers are essential for Na and pH homeostasis in all organisms. Human Na/H exchangers are of high medical interest, and insights into their structure and function are aided by the investigation of prokaryotic homologues. Most prokaryotic Na/H exchangers belong to either the Cation/Proton Antiporter (CPA) superfamily, the Ion Transport (IT) superfamily, or the Na-translocating Mrp transporter superfamily.

Mutation of two key aspartate residues alters stoichiometry of the NhaB Na/H exchanger from Klebsiella pneumoniae.

Bacterial NhaB Na/H exchangers belonging to the Ion Transporter superfamily are poorly characterized in contrast to Na/H exchangers of the Cation Proton Antiporter superfamily which have NhaA from Escherichia coli as a prominent member. For a more detailed understanding of the intricacies of the exchanger's transport mechanism, mutational studies are essential. Therefore, we mutated two protonatable residues present in the putative transmembrane region of NhaB from Klebsiella pneumoniae (KpNhaB), which could serve as substrate binding sites, Asp146 and Asp404, to either glutamate or alanine and analyzed transport function and stability of the mutants using electrophysiological and fluorimetric techniques.

Replacement of Lys-300 with a glutamine in the NhaA Na/H antiporter of yields a functional electrogenic transporter.

Much of the research on Na/H exchange has been done in prokaryotic models, mainly on the NhaA Na/H-exchanger from (EcNhaA). Two conserved aspartate residues, Asp-163 and Asp-164, are essential for transport and are candidates for possible binding sites for the two H that are exchanged for one Na to make the overall transport process electrogenic. More recently, a proposed mechanism of transport for EcNhaA has suggested direct binding of one of the transported H to the conserved Lys-300 residue, a salt bridge partner of Asp-163.

Competition is the basis of the transport mechanism of the NhaB Na+/H+ exchanger from Klebsiella pneumoniae.

Na+/H+ exchange is essential for survival of all organisms, having a role in the regulation of the intracellular Na+ concentration, pH and cell volume. Furthermore, Na+/H+ exchangers were shown to be involved in the virulence of the bacterium Yersinia pestis, indicating they might be potential targets for novel antibiotic treatments. The model system for Na+/H+ exchangers is the NhaA transporter from Escherichia coli, EcNhaA.

Lysine 300 is essential for stability but not for electrogenic transport of the NhaA Na/H antiporter.

Na/H antiporters are located in the cytoplasmic and intracellular membranes and play crucial roles in regulating intracellular pH, Na, and volume. The NhaA antiporter of is the best studied member of the Na/H exchanger family and a model system for all related Na/H exchangers, including eukaryotic representatives. Several amino acid residues are important for the transport activity of NhaA, including Lys-300, a residue that has recently been proposed to carry one of the two H ions that NhaA exchanges for one Na ion during one transport cycle.

Electrogenic Cation Binding in the Electroneutral Na+/H+ Antiporter of Pyrococcus abyssi.

Na/H antiporters in the CPA1 branch of the cation proton antiporter family drive the electroneutral exchange of H against Na ions and ensure pH homeostasis in eukaryotic and prokaryotic organisms. Although their transport cycle is overall electroneutral, specific partial reactions are electrogenic. Here, we present an electrophysiological study of the PaNhaP Na/H antiporter from Pyrococcus abyssi reconstituted into liposomes.

A universal mechanism for transport and regulation of CPA sodium proton exchangers.

Recent studies performed on a series of Na+/H+ exchangers have led us to postulate a general mechanism for Na+/H+ exchange in the monovalent cation/proton antiporter superfamily. This simple mechanism employs a single binding site for which both substrates compete. The developed kinetic model is self-regulatory, ensuring down-regulation of transport activity at extreme pH, and elegantly explains the pH-dependent activity of Na+/H+ exchangers.

Species differences in bacterial NhaA Na+/H+ exchangers.

Bacteria have adapted their NhaA Na(+)/H(+) exchangers responsible for salt homeostasis to their different habitats. We present an electrophysiological and kinetic analysis of NhaA from Helicobacter pylori and compare it to the previously investigated exchangers from Escherichia coli and Salmonella typhimurium. Properties of all three transporters are described by a simple model using a single binding site for H(+) and Na(+).

NhaA Na+/H+ antiporter mutants that hardly react to the membrane potential.

pH and Na+ homeostasis in all cells requires Na+/H+ antiporters. The crystal structure, obtained at pH 4, of NhaA, the main antiporter of Escherichia coli, has provided general insights into an antiporter mechanism and its unique pH regulation. Here, we describe a general method to select various NhaA mutants from a library of randomly mutagenized NhaA.

Keeping it simple, transport mechanism and pH regulation in Na+/H+ exchangers.

Na(+)/H(+) exchangers are essential for regulation of intracellular proton and sodium concentrations in all living organisms. We examined and experimentally verified a kinetic model for Na(+)/H(+) exchangers, where a single binding site is alternatively occupied by Na(+) or one or two H(+) ions. The proposed transport mechanism inherently down-regulates Na(+)/H(+) exchangers at extreme pH, preventing excessive cytoplasmic acidification or alkalinization.

Introduction to solid supported membrane based electrophysiology.

The electrophysiological method we present is based on a solid supported membrane (SSM) composed of an octadecanethiol layer chemisorbed on a gold coated sensor chip and a phosphatidylcholine monolayer on top. This assembly is mounted into a cuvette system containing the reference electrode, a chlorinated silver wire. After adsorption of membrane fragments or proteoliposomes containing the membrane protein of interest, a fast solution exchange is used to induce the transport activity of the membrane protein.

HPLC separation of acetaminophen and its impurities using a mixed-mode reversed-phase/cation exchange stationary phase.

Determination of acetaminophen and its main impurities: 4-nitrophenol, 4'-chloroacetanilide, as well as 4-aminophenol and its degradation products, p-benzoquinone and hydroquinone has been developed and validated by a new high-performance liquid chromatography method. Chromatographic separation has been obtained on a Hypersil Duet C18/SCX column, using gradient elution, with a mixture of phosphate buffer (pH = 4.88) and methanol as a mobile phase.