In vivo measurements of the internal pH of Hediste (Nereis) diversicolor (Annelida, Polychaeta) exposed to ambient sulphidic conditions using pH microelectrodes

Progress in pH-Sensitive sensors: essential tools for organelle pH detection, spotlighting mitochondrion and diverse applications

pH-sensitive fluorescent proteins have revolutionized the field of cellular imaging and physiology, offering insight into the dynamic pH changes that underlie fundamental cellular processes. This comprehensive review explores the diverse applications and recent advances in the use of pH-sensitive fluorescent proteins. These remarkable tools enable researchers to visualize and monitor pH variations within subcellular compartments, especially mitochondria, shedding light on organelle-specific pH regulation. They play pivotal roles in visualizing exocytosis and endocytosis events in synaptic transmission, monitoring cell death and apoptosis, and understanding drug effects and disease progression. Recent advancements have led to improved photostability, pH specificity, and subcellular targeting, enhancing their utility. Techniques for multiplexed imaging, three-dimensional visualization, and super-resolution microscopy are expanding the horizon of pH-sensitive protein applications. The future holds promise for their integration into optogenetics and drug discovery. With their ever-evolving capabilities, pH-sensitive fluorescent proteins remain indispensable tools for unravelling cellular dynamics and driving breakthroughs in biological research. This review serves as a comprehensive resource for researchers seeking to harness the potential of pH-sensitive fluorescent proteins.

Influence of pH on the toxicity of ionisable pharmaceuticals and personal care products to freshwater invertebrates

The majority of pharmaceuticals and personal health-care products are ionisable molecules at environmentally relevant pHs. The ionization state of these molecules in freshwater ecosystems may influence their toxicity potential to aquatic organisms. In this study we evaluated to what extent varying pH conditions may influence the toxicity of the antibiotic enrofloxacin (ENR) and the personal care product ingredient triclosan (TCS) to three freshwater invertebrates: the ephemeropteran Cloeon dipterum, the amphipod Gammarus pulex and the snail Physella acuta. Acute toxicity tests were performed by adjusting the water pH to four nominal levels: 6.5, 7.0, 7.5 and 8.0. Furthermore, we tested the efficiency of three toxicity models with different assumptions regarding the uptake and toxicity potential of ionisable chemicals with the experimental data produced in this study. The results of the toxicity tests indicate that pH fluctuations of only 1.5 units can influence EC50-48 h and EC50-96 h values by a factor of 1.4-2.7. Overall, the model that only focuses on the fraction of neutral chemical and the model that takes into account ion-trapping of the test molecules showed the best performance, although present limitations to perform risk assessments across a wide pH range (i.e., well above or below the substance pKa). Under such conditions, the model that takes into account the toxicity of the neutral and the ionized chemical form is preferred. The results of this study show that pH fluctuations can have a considerable influence on toxicity thresholds, and should therefore be taken into account for the risk assessment of ionisable pharmaceuticals and personal health-care products. Based on our results, an assessment factor of at least three should be used to account for toxicity differences between standard laboratory and field pH conditions. The models evaluated here can be used to perform refined risk assessments by taking into account the influence of temporal and spatial pH fluctuations on aquatic toxicity.

Lucina pectinata oxyhemoglobin (II-III) heterodimer pH susceptibility

Lucina pectinata live in high concentrations of hydrogen sulfide (H₂S) and contains one hemoglobin, Hemoglobin I (HbI), transporting H₂S and two hemoglobins, Hemoglobin II (HbII) and Hemoglobin (HbIII), transferring dioxygen to symbionts. HbII and HbIII contain B10 tyrosine (Tyr) and E7 glutamine (Gln) in the heme pocket generating an efficient hydrogen bonding network with the (HbII-HbIII)-O₂ species, leading to very low ligand dissociation rates. The results indicate that the oxy-hemeprotein is susceptible to pH from 4 to 9, at acidic conditions, and as a function of the potassium ferricyanide concentration, 100% of the met-aquo derivative is produced. Without a strong oxidant, pH 5 generates a small concentration of the met-aquo complex. The process is accelerated by the presence of salts, as indicated by the crystallization structures and UV-Vis spectra. The results suggest that acidic pH generates conformational changes associated with B10 and E7 heme pocket amino acids, weakening the (HbII-HbIII)-O₂ hydrogen bond network. The observation is supported by X-ray crystallography, since at pH 4 and 5, the heme-Fe tends to oxidize, while at pH 7, the oxy-heterodimer is present. Conformational changes also are observed at higher pH by the presence of a 605 nm transition associated with the iron heme-Tyr interaction. Therefore, pH is one crucial factor regulating the (HbII-HbIII)-O₂ complex hydrogen-bonding network. Thus, it can be proposed that the hydrogen bonding adjustments between the heme bound O₂ and the Tyr and Gln amino acids contribute to oxygen dissociation from the (HbII-HbIII)-O₂ system.

Design, calibration and application of broad-range optical nanosensors for determining intracellular pH

Particle-based nanosensors offer a tool for determining the pH in the endosomal-lysosomal system of living cells. Measurements providing absolute values of pH have so far been restricted by the limited sensitivity range of nanosensors, calibration challenges and the complexity of image analysis. This protocol describes the design and application of a polyacrylamide-based nanosensor (∼60 nm) that covalently incorporates two pH-sensitive fluorophores, fluorescein (FS) and Oregon Green (OG), to broaden the sensitivity range of the sensor (pH 3.1-7.0), and uses the pH-insensitive fluorophore rhodamine as a reference fluorophore. The nanosensors are spontaneously taken up via endocytosis and directed to the lysosomes where dynamic changes in pH can be measured with live-cell confocal microscopy. The most important focus areas of the protocol are the choice of pH-sensitive fluorophores, the design of calibration buffers, the determination of the effective range and especially the description of how to critically evaluate results. The entire procedure typically takes 2-3 weeks.

pH sensing in living cells using fluorescent microspheres

Intracellular pH in living cells is measured in real time at the single cell level using fluorescently covalently loaded microspheres as efficient carrier systems and stable sensors. The use of these sensors immobilized covalently onto polymeric particles allows analysis of intracellular pH flux over long period of time and eliminates the disadvantages such as dilution within the cell, elimination via leakage or compartmentalization.

Stress protein response in two sibling species of Marenzelleria (Polychaeta: Spionidae): Is there an influence of acclimation salinity?

The induction and synthesis of stress proteins in the polychaete sibling species Marenzelleria viridis and M. neglecta was investigated at two different acclimation salinities (10 and 25 ppt). By in vitro labeling of dissected metameres with (35)S-methionine/cysteine and electrophoretic separation, four size classes of heat shock proteins (Hsps) were detected corresponding to 86, 78, 75 and 27 kDa. All Hsps, with the exception of Hsp86, represent a complex of multiple isoforms. The sibling species differed in three aspects of their heat shock response: (1) the induction temperature for Hsp75 synthesis was 25 degrees C and 30 degrees C in M. viridis and M. neglecta, respectively; (2) the relative level of synthesis of Hsp75 was higher in M. viridis; (3) the heat shock response was inactivated at a higher temperature in M. neglecta compared to M. viridis. The results showed that acclimation salinity had no explicit effect on Hsp synthesis in either species and that M. viridis was thermally more sensitive than its sibling species. We proposed that temperature, alone or in combination with other abiotic factors, plays a far greater role in the biogeographic distribution in Marenzelleria spp. than has been estimated so far.