Transmembrane Movement Research Articles

Genome-wide identification and molecular evolution of elongation family of very long chain fatty acids proteins in Cyrtotrachelus buqueti

To reveal the molecular function of elongation family of very long chain fatty acids(ELO) protein in Cyrtotrachelus buqueti, we have identified 15 ELO proteins from C.buqueti genome. 15 CbuELO proteins were located on four chromosomes. Their isoelectric points ranged from 9.22 to 9.68, and they were alkaline. These CbuELO proteins were stable and hydrophobic. CbuELO proteins had transmembrane movement, and had multiple phosphorylation sites. The secondary structure of CbuELO proteins was mainly α-helix. A total of 10 conserved motifs were identified in CbuELO protein family. Phylogenetic analysis showed that molecular evolutionary relationships of ELO protein family between C. buqueti and Tribolium castaneum was the closest. Developmental transcriptome analysis indicated that CbuELO10, CbuELO13 and CbuELO02 genes were key enzyme genes that determine the synthesis of very long chain fatty acids in pupae and eggs, CbuELO6 and CbuELO7 were that in the male, and CbuELO8 and CbuELO11 were that in the larva. Transcriptome analysis under different temperature conditions indicated that CbuELO1, CbuELO5, CbuELO12 and CbuELO14 participated in regulating temperature stress responses. Transcriptome analysis at different feeding times showed CbuELO12 gene expression level in all feeding time periods was significant downregulation. The qRT-PCR experiment verified expression level changes of CbuELO gene family under different temperature and feeding time conditions. Protein-protein interaction analysis showed that 9 CbuELO proteins were related to each other, CbuELO1, CbuELO4 and CbuELO12 had more than one interaction relationship. These results lay a theoretical foundation for further studying its molecular function during growth and development of C. buqueti.

Identification of nonsense variants in the genomes of 15 Murciano-Granadina bucks and analysis of their segregation in parent-offspring trios

Nonsense variants can inactivate gene function by causing the synthesis of truncated proteins or by inducing nonsense mediated decay of messenger RNAs. The occurrence of such variants in the genomes of livestock species is modulated by multiple demographic and selective factors. Even though nonsense variants can have causal effects on embryo lethality, abortions, and disease, their genomic distribution and segregation in domestic goats have not been characterized in depth yet. In this work, we have sequenced the genomes of 15 Murciano-Granadina bucks with an average coverage of 32.92 × ± 1.45 × . Bioinformatic analysis revealed 947 nonsense variants consistently detected with SnpEff and Ensembl-VEP. These variants were especially abundant in the 3'end of the protein-coding regions. Genes related to olfactory perception, ATPase activity coupled to transmembrane movement of substances, defense to virus, hormonal response, and sensory perception of taste were particularly enriched in nonsense variants. Seventeen nonsense variants expected to have harmful effects on fitness were genotyped in parent-offspring trios. We observed that several nonsense variants predicted to be lethal based on mouse knockout data did not have such effect, a finding that could be explained by the existence of multiple mechanisms counteracting lethality. These findings demonstrate that predicting the effects of putative nonsense variants on fitness is extremely challenging. As a matter of fact, such a goal could only be achieved by generating a high quality telomere-to-telomere goat reference genome combined with carefully curated annotation and functional testing of promising candidate variants.

In situ monitoring and unveiling of [formula omitted] ions transmembrane process via sensitive fiber-optic plasmonic spectral combs

Potassium ions (K+) transmembrane transport is essential for regulating various physiological processes. Herein, a label-free tilted fiber Bragg grating (TFBG)-assisted plasmonic sensor was proposed and experimentally demonstrated for measuring K+ transmembrane movement in situ and continuously. The sensor was coated with valinomycin-modified vesicular liposome, providing an exceptional capability for selectively capturing and transporting K+ through the liposome’s bilayer membrane. A differential demodulation method was proposed, by which great advancements were achieved in unveiling K+ transmembrane process showing three stages in real time. In particular, not only does the sensor sensitively detect low K+ level (detection limit down to 8.5 pM) but also successively decouple bulk and surface effects involved in transmembrane dynamics, along with additional advantage of resistance to temperature and light power fluctuations. These advancements represent great progress in revealing K+ transmembrane movement and highlight the potential for monitoring transmembrane-related cellular signaling pathways like cell proliferation and apoptosis.

Unsaturation effects on lipid transmembrane asymmetry.

Within cell plasma membranes, unsaturated lipids are asymmetrically distributed over the inner and outer leaflets, offering an attractive local structural feature. However, the mechanism to keep lipid transmembrane asymmetry and the closely related transmembrane movement (flip-flop) for unsaturated lipids remain poorly understood. Here, we applied sum frequency generation vibrational spectroscopy to investigate this lipid transmembrane asymmetry upon mimicking the cell membrane homeostatic processes. On the one hand, unsaturated lipids were found to hinder the flip-flop process and preserve lipid transmembrane asymmetry in model cell membranes, owing to the steric hindrance caused by their bent tails. On the other hand, local unsaturated lipids in the mixed unsaturated/saturated lipid bilayer were conducive to the formation of the local asymmetry. Therefore, lipid unsaturation can be recognized as an intrinsic key factor to form and maintain lipid transmembrane asymmetry in cell membranes.

Verification of the analytical performance of the serum magnesium assay on Abbott Architect ci8200

Magnesium is recognized as the fourth most important cation in the body and the second most abundant intracellular cation, following potassium. Its physiological significance lies in its capacity to form complexes with crucial intracellular anionic ligands, notably ATP, and its ability to compete with calcium for specific binding sites on proteins and cell membranes. Over 300 enzyme reactions rely on magnesium. The concentration of free magnesium within cells determines the magnesium content of these enzymes. Magnesium influences myocardial contraction and the electrical activity of myocardial cells, as well as the specialized conduction systems of the fetus, by modulating the transmembrane movements of ions like sodium, potassium, and calcium. Furthermore, magnesium can affect the contractility of vascular smooth muscle, and alterations in intracellular magnesium levels may impact cell proliferation or contraction. Magnesium is involved in nucleic acid and protein metabolism, intermediary metabolism, energy production, and consumption reactions, and it plays specific roles in various physiological systems such as the neuromuscular and cardiovascular systems. Our research aims to assess the analytical accuracy of the serum magnesium assay method utilizing an Abbott kit on the Architect ci8200 automated system in the biochemistry laboratory of Mohammed VI University Hospital of Oujda. The evaluation of the kit's analytical accuracy was conducted within the flexible scope A by conducting a performance analysis on the Architect ci8200. We examined repeatability, reproducibility, measurement imprecision, and compared results between two Architect ci8200 instruments. All findings align with the acceptability criteria recommended by the supplier and the Valtec protocol of the Société Française de Biologie Clinique (SFBC), indicating overall satisfactory outcomes for the study. The Architect ci8200 automated system demonstrated satisfactory analytical performance for reliably determining serum magnesium levels. Method verification in medical laboratories is essential to guarantee the accuracy, precision, and reliability of test results. Verification entails confirming that the test method used is suitable for its intended purpose, yields result consistent with the claimed performance characteristics, and meets the laboratory's quality control and quality assurance standards.

Model of micro-metastases of breast cancer cells in ovarian tissue: Cryopreservation of ZR-75-1 and MDA-MB-231 cells with increased speed of warming increases malignancy

In medicine, ovarian tissue cryopreservation exists for fertility preservation of cancer patients. In fact, ovarian tissue frozen for subsequent thawing and re-transplantation can be contaminated with cancer cells. Therefore, investigations on the effect of cryopreservation on the post-thawed viability of such cells are relevant. Speed of warming is a key parameter of cell cryopreservation. However, the data about comparative viability of cancer cells cryopreserved with different parameters of warming are limited. The aim of our investigations was to assess the malignancy of cryopreserved cancer cells after conventional cooling followed by relatively slow and quick speed of warming. In vitro cultured breast cancer cells of lines ZR-75-1 and MD0MD-231 in form of compacted fragments (as a model of solid tumors) were frozen following a protocol usually used for freezing of ovarian tissue (6 % ethylene glycol+6 % glycerol+0.15 M sucrose, −0.3 °C/min). Cells were warmed by two routine regimes of warming: at 37 °C (“slow” warming) and 100 °C (“quick” warming). Biological properties of cells were investigated: viability, proliferation rate, 2D- and 3D-migration, transmembrane movement and invasion. Quick warming at 100 °C in comparison with slow warming at 37 °C exhibited significantly higher cell survival for MDA-MB-231 cells: 70.1 % vs. 63.2 % and for ZR-75-1 86.8 % vs. 82.9 %, respectively. The cell motility including 2D movement and 3D transmembrane migration were higher after quick thawing at 100 °C. Invasive abilities of cells after cryopreservation were higher than that of fresh (non-treated cells). Both thawing regimes showed a similar rate of cell proliferation. Cryopreservation procedures, and especially this one with quick thawing, increase malignancy of ZR-75-1 and MDA-MB-231 breast cancer cells and risk of metastasis.

Molecular Dynamics Simulations of the Mutated Proton-Transferring a-Subunit of E. coli FoF1-ATP Synthase.

The membrane Fo factor of ATP synthase is highly sensitive to mutations in the proton half-channel leading to the functional blocking of the entire protein. To identify functionally important amino acids for the proton transport, we performed molecular dynamic simulations on the selected mutants of the membrane part of the bacterial FoF1-ATP synthase embedded in a native lipid bilayer: there were nine different mutations of a-subunit residues (aE219, aH245, aN214, aQ252) in the inlet half-channel. The structure proved to be stable to these mutations, although some of them (aH245Y and aQ252L) resulted in minor conformational changes. aH245 and aN214 were crucial for proton transport as they directly facilitated H+ transfer. The substitutions with nonpolar amino acids disrupted the transfer chain and water molecules or neighboring polar side chains could not replace them effectively. aE219 and aQ252 appeared not to be determinative for proton translocation, since an alternative pathway involving a chain of water molecules could compensate the ability of H+ transmembrane movement when they were substituted. Thus, mutations of conserved polar residues significantly affected hydration levels, leading to drastic changes in the occupancy and capacity of the structural water molecule clusters (W1-W3), up to their complete disappearance and consequently to the proton transfer chain disruption.

Pan-cancer analysis of SLC2A family genes as prognostic biomarkers and therapeutic targets

BackgroundThe major facilitator superfamily glucose transporters (GLUTs), encoded by solute carrier 2A (SLC2A) genes, mediate the transmembrane movement and uptake of glucose. To satisfy the improved energy demands, glycolysis flux is increased in cancers compared with healthy tissues. Multiple diseases, including cancer, have been associated with GLUTs. Nevertheless, not much research has been done on the functions of SLC2As in pan-cancer prognosis or their clinical treatment potential. MethodsThe SLC2A family genes' level of expression and prognostic values were analyzed in relation to pan-cancer. We then examined the association among SLC2As expression and TME, Stemness score, clinical characteristics, immune subtypes, and drug sensitivity. We merged bioinformatics analysis techniques with up-to-date public databases. Additionally, SLC2As from the KOBAS database were subjected to enrichment analysis. ResultsWe discovered that SLC2As' gene expression differed significantly between normal tissues and many malignancies. A number of tumors from various databases demonstrate a relationship between prognosis and SLC2A family gene expression. For instance, SLC2A2 and SLC2A5 were associated with the overall survival (OS) of hepatocellular carcinoma. SLC2A1 was associated with the OS of lung adenocarcinoma and pancreatic adenocarcinoma. Moreover, the SLC2A family gene expression is significantly correlated with the pan-cancer stromal and immune scores, and the RNA and DNA stemness scores. Furthermore, we found that the majority of SLC2As had a strong correlation with the tumor stages in KIRC. The immunological subtypes and all members of the SLC2A gene family exhibited a substantial correlation. Moreover, pathways containing insulin resistance and adipocytokine signaling pathway may influence the progression of some cancers. Finally, there is a significant positive or negative connection between drug sensitivity and SLC2A1 expression. ConclusionOur research highlights the significant promise of SLC2As as prognostic indicators and offers insightful approaches for upcoming exploration of SLC2As as putative therapeutic targets in malignancies.

The 2-aminoethyl diphenylborinate-based fluorescent method identifies quercetin and luteolin metabolites as substrates of Organic anion transporting polypeptides, OATP1B1 and OATP2B1

Organic anion transporting polypeptides (OATPs), OATP1B1 and OATP2B1 are membrane proteins mediating the cellular uptake of chemically diverse organic compounds. OATP1B1 is exclusively expressed in hepatocytes and plays a key role in hepatic detoxification. The ubiquitously expressed OATP2B1 promotes the intestinal absorption of orally administered drugs. Flavonoids are widely found in foods and beverages, and many of them can inhibit OATP function, resulting in food-drug interactions. In our previous work, we have shown that not only luteolin (LUT) and quercetin (Q), but also some of their metabolites can inhibit OATP1B1 and OATP2B1 activity. However, data about the potential direct transport of these flavonoids by OATPs have been incomplete. Hence, in the current study, we developed a simple, fluorescence-based method for the measurement of intracellular flavonoid levels. The method applies a cell-permeable small molecule (2-aminoethyl diphenylborinate, 2-APB), that, upon forming a complex with flavonoids, results in their fluorescence enhancement. This way the direct uptake of LUT and Q, and also their metabolites' could be investigated both by confocal microscopy and in a fluorescence plate reader in living cells. With this approach we identified quercetin-3′-O-sulfate, luteolin-3′-O-glucuronide, luteolin-7-O-glucuronide and luteolin-3′-O-sulfate as substrates of both OATP1B1 and OATP2B1. Our results highlight that OATP1B1 and OATP2B1 can be key participants in the transmembrane movement of LUT and Q conjugates with otherwise low cell permeability. In addition, the novel method developed in this study can be a good completion to existing fluorescence-based assays to investigate OATP function.

Structural Insights and Influence of Terahertz Waves in Midinfrared Region on Kv1.2 Channel Selectivity Filter.

Potassium ion channels are the structural basis for excitation transmission, heartbeat, and other biological processes. The selectivity filter is a critical structural component of potassium ion channels, whose structure is crucial to realizing their function. As biomolecules vibrate and rotate at frequencies in the terahertz band, potassium ion channels are sensitive to terahertz waves. Therefore, it is worthwhile to investigate how the terahertz wave influences the selectivity filter of the potassium channels. In this study, we investigate the structure of the selectivity filter of Kv1.2 potassium ion channels using molecular dynamics simulations. The effect of an electric field on the channel has been examined at four different resonant frequencies of the carbonyl group in SF: 36.75 37.06, 37.68, and 38.2 THz. As indicated by the results, 376GLY appears to be the critical residue in the selectivity filter of the Kv1.2 channel. Its dihedral angle torsion is detrimental to the channel structural stability and the transmembrane movement of potassium ions. 36.75 THz is the resonance frequency of the carbonyl group of 376GLY. Among all four frequencies explored, the applied terahertz electric field of this frequency has the most significant impact on the channel structure, negatively impacting the channel stability and reducing the ion permeability by 20.2% compared to the absence of fields. In this study, we simulate that terahertz waves in the mid-infrared frequency region can significantly alter the structure and function of potassium ion channels and that the effects of terahertz waves differ greatly based on frequency.

Transcendent Aspects of Proton Channels.

A handful of biological proton-selective ion channels exist. Some open at positive or negative membrane potentials, others open at low or high pH, and some are light activated. This review focuses on common features that result from the unique properties of protons. Proton conduction through water or proteins differs qualitatively from that of all other ions. Extraordinary proton selectivity is needed to ensure that protons permeate and other ions do not. Proton selectivity arises from a proton pathway comprising a hydrogen-bonded chain that typically includes at least one titratable amino acid side chain. The enormously diverse functions of proton channels in disparate regions of the phylogenetic tree can be summarized by considering the chemical and electrical consequences of proton flux across membranes. This review discusses examples of cells in which proton efflux serves to increase pHi, decrease pHo, control the membrane potential, generate action potentials, or compensate transmembrane movement of electrical charge.

Structural mechanisms of the human cardiac sodium-calcium exchanger NCX1

Na+/Ca2+ exchangers (NCX) transport Ca2+ in or out of cells in exchange for Na+. They are ubiquitously expressed and play an essential role in maintaining cytosolic Ca2+ homeostasis. Although extensively studied, little is known about the global structural arrangement of eukaryotic NCXs and the structural mechanisms underlying their regulation by various cellular cues including cytosolic Na+ and Ca2+. Here we present the cryo-EM structures of human cardiac NCX1 in both inactivated and activated states, elucidating key structural elements important for NCX ion exchange function and its modulation by cytosolic Ca2+ and Na+. We demonstrate that the interactions between the ion-transporting transmembrane (TM) domain and the cytosolic regulatory domain define the activity of NCX. In the inward-facing state with low cytosolic [Ca2+], a TM-associated four-stranded β-hub mediates a tight packing between the TM and cytosolic domains, resulting in the formation of a stable inactivation assembly that blocks the TM movement required for ion exchange function. Ca2+ binding to the cytosolic second Ca2+-binding domain (CBD2) disrupts this inactivation assembly which releases its constraint on the TM domain, yielding an active exchanger. Thus, the current NCX1 structures provide an essential framework for the mechanistic understanding of the ion transport and cellular regulation of NCX family proteins.

Cloning, Bioinformatics Analysis and Physiological Function of the Pine Wood Nematode Bxadh2 Gene

In previous research, the pine wood nematode Bxadh2 gene significantly increased its expression in pine seedlings inoculated with endophytic Bacillus cereus GD2 and pine wood nematode. To explore pine wood nematode Bxadh2 gene function, we cloned and analyzed its biological information, and we preliminarily studied its physiological function through RNA interference. We found that the Bxadh2 gene’s full CDS length is 1269 bp, which encodes 422 amino acids, and presents a relatively stable hydrophobic protein. The protein encoded by the Bxadh2 gene has no signal peptide or transmembrane structure, and it is an intracellular protein that does not participate in transmembrane movement. The RNAi interference results showed that when the pine wood nematode’s Bxadh2 gene was suppressed, its survival rate and fecundity significantly decreased, indicating that the expression of the Bxadh2 gene was related to the growth and development of pine wood nematodes.

Efficient production of 2-keto-L-gulonic acid from D-glucose in Gluconobacter oxydans ATCC9937 by mining key enzyme and transporter

Direct production of 2-keto-L-gulonic acid (2-KLG, the precursor of vitamin C) from D-glucose through 2,5-diketo-D-gluconic acid (2,5-DKG) is a promising alternative route. To explore the pathway of producing 2-KLG from D-glucose, Gluconobacter oxydans ATCC9937 was selected as a chassis strain. It was found that the chassis strain naturally has the ability to synthesize 2-KLG from D-glucose, and a new 2,5-DKG reductase (DKGR) was found on its genome. Several major issues limiting production were identified, including the insufficient catalytic capacity of DKGR, poor transmembrane movement of 2,5-DKG and imbalanced D-glucose consumption flux inside and outside of the host strain cells. By identifying novel DKGR and 2,5-DKG transporter, the whole 2-KLG biosynthesis pathway was systematically enhanced by balancing intracellular and extracellular D-glucose metabolic flux. The engineered strain produced 30.5 g/L 2-KLG with a conversion ratio of 39.0%. The results pave the way for a more economical large-scale fermentation process for vitamin C.

Non-Aquaporin Water Channels.

Water transport through membrane is so intricate that there are still some debates. AQPs are entirely accepted to allow water transmembrane movement depending on osmotic gradient. Cotransporters and uniporters, however, are also concerned in water homeostasis. UT-B has a single-channel water permeability that is similar to AQP1. CFTR was initially thought as a water channel but now not believed to transport water directly. By cotransporters, such as KCC4, NKCC1, SGLT1, GAT1, EAAT1, and MCT1, water is transported by water osmosis coupling with substrates, which explains how water is transported across the isolated small intestine. This chapter provides information about water transport mediated by other membrane proteins except AQPs.

Network Pharmacology-Based Exploration of the Mechanism of Action of Shugan Hewei Recipe in the Treatment of Gastroesophageal Reflux Disease with Anxiety and Depression.

The Shugan Hewei recipe (SHR) is a well-recognized traditional Chinese medicine (TCM) prescription that has been shown to significantly improve chest pain, acid regurgitation, and the mood of GERD. Nonetheless, the underlying mechanisms remain unclear. In this study, the active compounds and targets of SHR were predicted using network pharmacology. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were utilized to explore the therapeutic mechanism of SHR. Combined with the drug target obtained from network pharmacology, the therapeutic effect and mechanism of SHR were observed. SHR's main active compounds included quercetin, kaempferol, and luteolin. The core targets of SHR and GERD were TGF-β1, IL-1β, IL-4, CXCL10, MAPK1, MAPK3, CXCL8, IL-10, IL-2, and FOS, involving virus infection, inflammatory response, and body immunity. The core targets of SHR during the treatment of mental disorders were GABRA1, GABRA2, GABRA3, GABRA5, and GABRA6, involving synaptic transmission and transmembrane movement. Animal experiments revealed that SHR could repair the lower esophageal mucosa, mediate inflammatory factors, and GABA receptors and improve the behavior of rats. Overall, our results substantiate that SHR has huge prospects for widespread application in treating GERD subjects with anxiety and depression.

MicroRNAs-mediated regulation of glucose transporter (GLUT) expression in glioblastoma.

Current knowledge about the role of microRNAs (miRNAs) in tumor glucose metabolism is growing, and a number of studies regularly confirm the impact miRNAs can have on glucose metabolism reprogramming in tumors. However, there remains a lack of understanding of the broader perspective on the role of miRNAs in energy reprogramming in glioblastoma. An important role in the metabolism of glucose is played by carrier proteins that ensure its transmembrane movement. Carrier proteins in mammalian cells are glucose transporters (GLUTs). In total, 12 types of GLUTs are distinguished, differing in localization, affinity for glucose and ability to regulate. The fact of increased consumption of glucose in tumors compared to non-proliferating normal tissues is known. Tumor cells need glucose to ensure their survival and growth, so the type of transport proteins like GLUT are critical for them. Previous studies have shown that GLUT-1 and GLUT-3 may play an important role in the development of some types of malignant tumors, including glioblastoma. In addition, there is evidence of how GLUT-1 and GLUT-3 expression is regulated by miRNAs in glioblastoma. Thus, the aim of this study is to highlight the role of specific miRNAs in modulating GLUT levels in order to take into account the use of miRNAs expression modulators as a useful strategy to increase the sensitivity of glioblastoma to current therapies.

Palmitoylation regulates cellular distribution of and transmembrane Ca flux through TrpM7

The bifunctional cation channel/kinase TrpM7 is ubiquitously expressed and regulates embryonic development and pathogenesis of several common diseases. The TrpM7 integral membrane ion channel domain regulates transmembrane movement of divalent cations, and its kinase domain controls gene expression via histone phosphorylation. Mechanisms regulating TrpM7 are elusive. It exists in two populations in the cell: at the cell surface where it controls divalent cation fluxes, and in intracellular vesicles where it controls zinc uptake and release. Here we report that TrpM7 is palmitoylated at a cluster of cysteines at the C terminal end of its Trp domain. Palmitoylation controls the exit of TrpM7 from the endoplasmic reticulum and the distribution of TrpM7 between cell surface and intracellular pools. Using the Retention Using Selective Hooks (RUSH) system, we demonstrate that palmitoylated TrpM7 traffics from the Golgi to the surface membrane whereas non-palmitoylated TrpM7 is sequestered in intracellular vesicles. We identify the Golgi-resident enzyme zDHHC17 and surface membrane-resident enzyme zDHHC5 as responsible for palmitoylating TrpM7 and find that TrpM7-mediated transmembrane calcium uptake is significantly reduced when TrpM7 is not palmitoylated. The closely related channel/kinase TrpM6 is also palmitoylated on the C terminal side of its Trp domain. Our findings demonstrate that palmitoylation controls ion channel activity of TrpM7 and that TrpM7 trafficking is dependant on its palmitoylation. We define a new mechanism for post translational modification and regulation of TrpM7 and other Trps.

NanoSuit-Assisted Liquid-Cell Scanning Electron Microscopy Enables Dynamic Gold Nanoparticle Monitoring for the Aggregation and Transmembrane Processes in Living Cells.

Dynamic observation of the behaviors of nanomaterials in the cellular environment is of great significance in mechanistic investigations on nanomaterial-based diagnostics and therapeutics. Realizing label-free observations with nanometer resolution is necessary but still has major challenges. Herein, we propose a NanoSuit-assisted liquid-cell scanning electron microscopy (NanoSuit-LCSEM) method that enables imaging of the behaviors of nanoparticles in living cells. Taking A549 cells and gold nanoparticles (AuNPs) as a cell-nanoparticle interaction model, the NanoSuit-LCSEM method showed a significantly improved resolution to 10 nm, which is high enough to distinguish single and two adjacent 30 nm AuNPs in cells. The continuous observation time for living cells is extended to 30 min, and the trajectories and velocities for the transmembrane movement of AuNP aggregates are obtained. This study provides a new approach for dynamic observation of nanomaterials in intact living cells and will greatly benefit the interdisciplinary research of nanomaterials, nanomedicine, and nanotechnology.

Extracellular K+ reflects light-evoked changes in retinal energy metabolism

Retinal neurons spend most of their energy to support the transmembrane movement of ions. Light-induced electrical activity is associated with a redistribution of ions, which affects the energy demand and results in a change in metabolism. Light-induced metabolic changes are expected to be different in distal and proximal retina due to differences in the light responses of different retinal cells. Extracellular K+ concentration ([K+]o) is a reliable indicator of local electrophysiological activity, and the purpose of this work was to compare [K+]o changes evoked by steady and flickering light in distal and proximal retina. Data were obtained from isolated mouse (C57Bl/6J) retinae. Double-barreled K+-selective microelectrodes were used to simultaneously record [K+]o and local ERGs. In the distal retina, photoreceptor hyperpolarization led to suppression of ion transfer, a decrease in [K+]o by 0.3–0.5 mM, reduced energy demand, and, as previously shown in vivo, decreased metabolism. Flickering light had the same effect on [K+]o in the distal retina as steady light of equivalent illumination. The conductance and voltage changes in postreceptor neurons are cell-specific, but the overall effect of steady light in the proximal retina is excitation, which is reflected in a [K+]o increase there (by a maximum of 0.2 mM). In steady light the [K+]o increase lasts only 1–2 s, but a sustained [K+]o increase is evoked by flickering light. A squarewave low frequency (1 Hz) flicker of photopic intensity produced the largest increases in [K+]o. Judging by measurements of [K+]o, steady illumination decreases energy metabolism in the distal retina, but not in the proximal retina (except for the first few seconds). Flickering light evokes the same decrease in the distal retina, but also evokes a sustained [K+]o increase in the proximal retina, suggesting an increase of metabolic demand there, especially at 1 Hz, when neurons of both on- and off-pathways appear to contribute maximally. This proximal retinal metabolic response to flicker correlates to the increase in blood flow during flicker that constitutes neurovascular coupling.