Hypoosmotic test in equine spermatozoa

The aim of the study was to evaluate equine sperm membrane integrity using the hypoosmotic swelling (HOS) test and to correlate this test with different sperm parameters in raw and frozen thawed semen. The HOS solutions were made with fructose, sucrose, lactose and sodium citrate each at 300, 150, 100, 50 and 25 mosm. Maximum numbers of swollen spermatozoa were observed in solutions of fructose, sucrose and lactose each at 100, 50 and 25 mosm. Correlations between progressive motility, morphologically normal spermatozoa and the HOS test were r = 0.75 and r = 0.51 in raw semen and r = 0.26 and r = -0.22 in frozen-thawed semen. The correlation between HOS and percentage of intact membranes with the fluorescent stain was r = 0.32 in frozen-thawed semen. The HOS test is a simple and accessible method which could be used as a complement to routine equine semen analysis. It has the added advantages of being less susceptible to the immediate effects of cold shock and of evaluating individual spermatozoa rather than the population as a whole, as does progressive motility.

Tryptophan 207 is crucial to the unique properties of the human voltage-gated proton channel, hHV1

Part of the "signature sequence" that defines the voltage-gated proton channel (H(V1)) is a tryptophan residue adjacent to the second Arg in the S4 transmembrane helix: RxWRxxR, which is perfectly conserved in all high confidence H(V1) genes. Replacing Trp207 in human HV1 (hH(V1)) with Ala, Ser, or Phe facilitated gating, accelerating channel opening by 100-fold, and closing by 30-fold. Mutant channels opened at more negative voltages than wild-type (WT) channels, indicating that in WT channels, Trp favors a closed state. The Arrhenius activation energy, Ea, for channel opening decreased to 22 kcal/mol from 30-38 kcal/mol for WT, confirming that Trp207 establishes the major energy barrier between closed and open hH(V1). Cation-π interaction between Trp207 and Arg211 evidently latches the channel closed. Trp207 mutants lost proton selectivity at pHo >8.0. Finally, gating that depends on the transmembrane pH gradient (ΔpH-dependent gating), a universal feature of H(V1) that is essential to its biological functions, was compromised. In the WT hH(V1), ΔpH-dependent gating is shown to saturate above pHi or pHo 8, consistent with a single pH sensor with alternating access to internal and external solutions. However, saturation occurred independently of ΔpH, indicating the existence of distinct internal and external pH sensors. In Trp207 mutants, ΔpH-dependent gating saturated at lower pHo but not at lower pHi. That Trp207 mutation selectively alters pHo sensing further supports the existence of distinct internal and external pH sensors. Analogous mutations in H(V1) from the unicellular species Karlodinium veneficum and Emiliania huxleyi produced generally similar consequences. Saturation of ΔpH-dependent gating occurred at the same pHo and pHi in H(V1) of all three species, suggesting that the same or similar group(s) is involved in pH sensing. Therefore, Trp enables four characteristic properties: slow channel opening, highly temperature-dependent gating kinetics, proton selectivity, and ΔpH-dependent gating.

Helminths of hawksbill turtle (Eretmochelys imbricata) from the Pacific coast of Costa Rica

Parasitological examination of a stranded hawksbill turtle (Eretmochelys imbricata) from Pacific coast of Costa Rica revealed the presence of a rich digenean fauna including Carettacola stunkardi (Spirorchiidae), Enodiotrema reductum (Plagiorchiidae), Cricocephalus albus, Adenogaster serialis, Epi-bathra crassa, Pleurogonius lobatus, P. trigonocephalus, P. linearis, and Pyelosomum posterorchis (Pronocephalidae). All helminths except C. albus and P. lobatus represent new geographical records for Costa Rica. Carettacola stunkardi is reported for first time in an Eastern Pacific hawksbill turtle and its pathological changes are here described. Histologically, nodular lesions on the serosal surface of intestine revealed a mixed infiltrate of heterophils, lymphocytes, and histiocytes within necrotic debris. Granulomas with spirorchiid eggs were observed in the mucosa, sub-mucosa and muscular layers of stomach and intestine, gallbladder and liver.

Assessing Structural Determinants of Zn2+ Binding to Human HV1 via Multiple MD Simulations

Voltage-gated proton channels (H_V1) are essential for various physiological tasks but are strongly inhibited by Zn²⁺ cations. Some determinants of Zn²⁺ binding have been elucidated experimentally and in computational studies. However, the results have always been interpreted under the assumption that Zn²⁺ binds to monomeric H_V1 despite evidence that H_V1 expresses as a dimer and that the dimer has a higher affinity for zinc than the monomer and experimental data that suggest coordination in the dimer interface. The results of former studies are also controversial, e.g., supporting either one single or two binding sites. Some structural determinants of the binding are still elusive. We performed a series of molecular dynamics simulations to address different structures of the human proton channel, the monomer and two plausible dimer conformations, to compare their respective potential to interact with and bind Zn²⁺ via the essential histidines. The series consisted of several copies of the system to generate independent trajectories and increase the significance compared to a single simulation. The amount of time simulated totals 29.9 μs for 126 simulations of systems comprising ∼59,000 to ∼187,000 atoms. Our approach confirms the existence of two binding sites in monomeric and dimeric human H_V1. The dimer interface is more efficient for attracting and binding Zn²⁺ via the essential histidines than the monomer or a dimer with the histidines in the periphery. The higher affinity is due to the residues in the dimer interface that create an attractive electrostatic potential funneling the zinc cations toward the binding sites.

Zinc modulation of proton currents in a new voltage-gated proton channel suggests a mechanism of inhibition

The H_V1 voltage‐gated proton (H_V1) channel is a key component of the cellular proton extrusion machinery and is pivotal for charge compensation during the respiratory burst of phagocytes. The best‐described physiological inhibitor of H_V1 is Zn²⁺. Externally applied ZnCl₂ drastically reduces proton currents reportedly recorded in Homo sapiens, Rattus norvegicus, Mus musculus, Oryctolagus cuniculus, Rana esculenta, Helix aspersa, Ciona intestinalis, Coccolithus pelagicus, Emiliania huxleyi, Danio rerio, Helisoma trivolvis, and Lingulodinium polyedrum, but with considerable species variability. Here, we report the effects of Zn²⁺ and Cd²⁺ on H_V1 from Nicoletia phytophila, NpH_V1. We introduced mutations at potential Zn²⁺ coordination sites and measured Zn²⁺ inhibition in different extracellular pH, with Zn²⁺ concentrations up to 1000 μm. Zn²⁺ inhibition in NpH_V1 was quantified by the slowing of the activation time constant and a positive shift of the conductance–voltage curve. Replacing aspartate in the S3‐S4 loop with histidine (D145H) enhanced both the slowing of activation kinetics and the shift in the voltage–conductance curve, such that Zn²⁺ inhibition closely resembled that of the human channel. Histidine is much more effective than aspartate in coordinating Zn²⁺ in the S3‐S4 linker. A simple Hodgkin Huxley model of NpH_V1 suggests a decrease in the opening rate if it is inhibited by zinc or cadmium. Limiting slope measurements and high‐resolution clear native gel electrophoresis (hrCNE) confirmed that NpH_V1 functions as a dimer. The data support the hypothesis that zinc is coordinated in between the dimer instead of the monomer. Zinc coordination sites may be potential targets for drug development.

The pH-dependent gating of the human voltage-gated proton channel from computational simulations

Gating of the voltage-gated proton channel H_V1 is strongly controlled by pH. There is evidence that this involves the sidechains of titratable amino acids that change their protonation state with changes of the pH. Despite experimental investigations to identify the amino acids involved in pH sensing only few progress has been made, including one histidine at the cytoplasmic side of the channel that is involved in sensing cellular pH. We have used constant pH molecular dynamics simulations in symmetrical and asymmetrical pH conditions across the membrane to investigate the pH- and ΔpH-dependent gating of the human H_V1 channel. Therefore, the pK_a of every titratable amino acids has been assessed in single simulations. Our simulations captured initial conformational changes between a deactivated and an activated state of the channel induced solely by changes of the pH. The pH-dependent gating is accompanied by an outward displacement of the three S4 voltage sensing arginines that moves the second arginine past the hydrophobic gasket (HG) which separates the inner and outer pores of the channel. H_V1 activation, when outer pH increases, involves amino acids at the extracellular entrance of the channel that extend the network of interactions from the external solution down to the HG. Whereas, amino acids at the cytoplasmic entrance of the channel are involved in activation, when inner pH decreases, and in a network of interactions that extend from the cytoplasm up to the HG.

Trapped Pore Waters in the Open Proton Channel HV 1

The voltage-gated proton channel, H_V 1, is crucial for innate immune responses. According to alternative hypotheses, protons either hop on top of an uninterrupted water wire or bypass titratable amino acids, interrupting the water wire halfway across the membrane. To distinguish between both hypotheses, the water mobility for the putative case of an uninterrupted wire is estimated. The predicted single-channel water permeability 2.3 × 10^-12 cm³ s^-1 reflects the permeability-governing number of hydrogen bonds between water molecules in single-file configuration and pore residues. However, the measured unitary water permeability does not confirm the predicted value. Osmotic deflation of reconstituted lipid vesicles reveals negligible water permeability of the H_V 1 wild-type channel and the D174A mutant open at 0 mV. The conductance of 1400 H⁺ s^-1 per wild-type channel agrees with the calculated diffusion limit for a ≈2 Å capture radius for protons. Removal of a charged amino acid (D174) at the pore mouth decreases H⁺ conductance by reducing the capture radius. At least one intervening amino acid contributes to H⁺ conductance while interrupting the water wire across the membrane.

Unexpected expansion of the voltage-gated proton channel family

Voltage-gated ion channels, whose first identified function was to generate action potentials, are divided into subfamilies with numerous members. The family of voltage-gated proton channels (HV ) is tiny. To date, all species found to express HV have exclusively one gene that codes for this unique ion channel. Here we report the discovery and characterization of three proton channel genes in the classical model system of neural plasticity, Aplysia californica. The three channels (AcHV 1, AcHV 2, and AcHV 3) are distributed throughout the whole animal. Patch-clamp analysis confirmed proton selectivity of these channels but they all differed markedly in gating. AcHV 1 gating resembled HV in mammalian cells where it is responsible for proton extrusion and charge compensation. AcHV 2 activates more negatively and conducts extensive inward proton current, properties likely to acidify the cytosol. AcHV 3, which differs from AcHV 1 and AcHV 2 in lacking the first arginine in the S4 helix, exhibits proton selective leak currents and weak voltage dependence. We report the expansion of the proton channel family, demonstrating for the first time the expression of three functionally distinct proton channels in a single species.

Zinc accelerates respiratory burst termination in human PMN

The respiratory burst of phagocytes is essential for human survival. Innate immune defence against pathogens relies strongly on reactive oxygen species (ROS) production by the NADPH oxidase (NOX2). ROS kill pathogens while the translocation of electrons across the plasma membrane via NOX2 depolarizes the cell. Simultaneously, protons are released into the cytosol. Here, we compare freshly isolated human polymorphonuclear leukocytes (PMN) to the granulocytes-like cell line PLB 985. We are recording ROS production while inhibiting the charge compensating and pH regulating voltage-gated proton channel (H_V1). The data suggests that human PMN and the PLB 985 generate ROS via a general mechanism, consistent of NOX2 and H_V1. Additionally, we advanced a mathematical model based on the biophysical properties of NOX2 and H_V1. Our results strongly suggest the essential interconnection of H_V1 and NOX2 during the respiratory burst of phagocytes. Zinc chelation during the time course of the experiments postulates that zinc leads to an irreversible termination of the respiratory burst over time. Flow cytometry shows cell death triggered by high zinc concentrations and PMA. Our data might help to elucidate the complex interaction of proteins during the respiratory burst and contribute to decipher its termination.

Editorial for 'Issue focus on 2nd Costa Rica biophysics symposium - March 11th-12th, 2021'

This Editorial describes both the motivation for, and the five articles appearing in, the Issue Focus dedicated to the 2nd Costa Rica Biophysics Symposium which was held in March 2021. Some recent history about both the symposium and developments in science occurring within Costa Rica is described. 

Voltage-gated proton channels in polyneopteran insects

Voltage‐gated proton channels (H_V1) are expressed in eukaryotes, including basal hexapods and polyneopteran insects. However, currently, there is little known about H_V1 channels in insects. A characteristic aspartate (Asp) that functions as the proton selectivity filter (SF) and the RxWRxxR voltage‐sensor motif are conserved structural elements in H_V1 channels. By analysing Transcriptome Shotgun Assembly (TSA) databases, we found 33 polyneopteran species meeting these structural requirements. Unexpectedly, an unusual natural variation Asp to glutamate (Glu) at SF was found in Phasmatodea and Mantophasmatodea. Additionally, we analysed the expression and function of H_V1 in the phasmatodean stick insect Extatosoma tiaratum (Et). EtH_V1 is strongly expressed in nervous tissue and shows pronounced inward proton conduction. This is the first study of a natural occurring Glu within the SF of a functional H_V1 and might be instrumental in uncovering the physiological function of H_V1 in insects.

Proton channels in molluscs: A new bivalvian-specific minimal HV 4 channel

Recently, three proton channels (H_V ) have been identified and characterized in Aplysia californica (AcH_V 1-3). Focusing on AcH_V 1 and AcH_V 2, analysis of Transcriptome Shotgun Assembly and genomic databases of 91 molluscs identified H_V homologous channels in other molluscs: channels homologous to AcH_V 1 and to AcH_V 2 were found in 90 species (56 full-length sequences) and in 33 species (18 full-length sequences), respectively. Here, we report the discovery of a fourth distinct proton channel family, H_V 4. This new family has high homology to AcH_V 1 and AcH_V 2 and was identified only in bivalvian molluscs (13 species, 12 full-length sequences). Typically, these channels possess an extracellular S1-S2 loop of intermediate size (~ 20 amino acids) compared to the shorter loops of molluscan H_V 1 channels (~ 13 amino acids) and the much larger loops of molluscan H_V 2 channels (> 65 amino acids). The characteristic voltage-sensor motif in S4 possesses only two arginine residues with the common third arginine being replaced by a lysine. Moreover, H_V 4 channels are much smaller with only around 200 amino acids in total length. The smallest functional channel found so far in nature (189 amino acids) is expressed in the pacific oyster Crassostrea gigas (CgH_V 4) and might be considered an archetypical minimal proton channel. Functional expression and electrophysiological characterization demonstrated that CgH_V 4 shares distinctive hallmarks of other investigated proton channels as high proton selectivity, slow activation, and pH- and voltage-regulated gating. This work is the first description of a H_V 4 type channel, adding a new member to the recently expanded family of proton channels.

Semi-automatic algorithm to build finite element numerical models of the human hearing system from Micro-CT data

Finite Element modeling has been an extended methodology to build numerical model to simulate the behavior of the hearing system. Due to the complexity of the system and the difficulties to reduce the uncertainties of the geometric data, they result in computationally expensive models, sometimes generic, representative of average geometries. It makes it difficult to validate the model with direct experimental data from the same specimen or to establish a patient-oriented modeling strategy. In the present paper, a first attempt to automatize the process of model building is made. The source information is geometrical information obtained from CT of the different elements that compose the system. Importing that data, we have designed the complete procedure to build a model including tympanic membrane, ossicular chain and cavities. The methodology includes the proper coupling of all the elements and the generation of the corresponding finite element model. The whole automatic procedure is not complete, as we need to make some human-assisted decisions; however, the model development time is reduced from 4 weeks to approximately 3 days. The goal of the modeling algorithm is to build a Finite Element Model with a limited computational cost. Several tasks as contour identification or model decimation are designed and integrated in order to follow a semi-automated process that allows generating a patient-oriented model.

Avaliação das Propriedades Físico-Químicas de Diferentes Pastas de Hidróxido de Cálcio

O objetivo deste trabalho foi avaliar e comparar a composic,ão química e a radiopacidade de diferentes pastas de hidróxido de cálcio. Foram avaliadas treˆs pastas comerciais: Ultracal XS Hydropast e Callen. O hidróxido de cálcio PA foi utilizado como controle. Para avaliar a composição química dos materiais, uma amostra de cada pasta foi avaliada por análise termogravimétrica, e a massa de hidróxido de cálcio presente foi obtida através de cálculos estequiométricos a partir da decomposic,ão térmica de suas moléculas. Para avaliar a radiopacidade, foram analisadas 03 amostras para cada grupo. A radiopacidade foi avaliada com um sistema de radiografia digital indireta EXPRESS e equipamento de raios X FOCUS. As imagens obtidas foram analisadas quanto aos padrões do valor de cinza através do software ImageJ. Os percentuais de massa de hidróxido de cálcio obtidos para cada material foram: hidróxido de cálcio PA: 87,12% Ultracal XS: 36,38% Hydropast: 30,66% Callen: 50,54%. Os valores de escala de cinza das pastas foram de: 63,41 para o hidróxido de cálcio PA 126,35 para Ultracal XS 106,73 para Hydropast, e 72,23 para Callen. Na mesma análise, a escala de alumínio apresentou os valores: Al 1mm: 53,50 Al 4 mm:  98,06 Al 8mm:  162,14 Al 12mm: 205,4. Houve diferenc,as em todas as pastas entre a quantidade de hidróxido de cálcio informada pelo fabricante e a quantidade encontrada nas análises termogravimétricas. As pastas comerciais testadas apresentaram maior radiopacidade que o grupo controle. A Ultracal XS foi o material com maior radiopacidade, seguido da Hydropast e Callen.Palavras-chave: Hidróxido de Cálcio. Termogravimetria. Radiografia.

Interaction with stomatin directs human proton channels into cholesterol-dependent membrane domains

Many membrane proteins are modulated by cholesterol. Here we report profound effects of cholesterol depletion and restoration on the human voltage-gated proton channel, hHV1, in excised patches but negligible effects in the whole-cell configuration. Despite the presence of a putative cholesterol-binding site, a CARC motif in hHV1, mutation of this motif did not affect cholesterol effects. The murine HV1 lacks a CARC sequence but displays similar cholesterol effects. These results argue against a direct effect of cholesterol on the HV1 protein. However, the data are fully explainable if HV1 preferentially associates with cholesterol-dependent lipid domains, or "rafts." The rafts would be expected to concentrate in the membrane/glass interface and to be depleted from the electrically accessible patch membrane. This idea is supported by evidence that HV1 channels can diffuse between seal and patch membranes when suction is applied. Simultaneous truncation of the large intracellular N and C termini of hHV1 greatly attenuated the cholesterol effect, but C truncation alone did not; this suggests that the N terminus is the region of attachment to lipid domains. Searching for abundant raft-associated proteins led to stomatin. Co-immunoprecipitation experiment results were consistent with hHV1 binding to stomatin. The stomatin-mediated association of HV1 with cholesterol-dependent lipid domains provides a mechanism for cells to direct HV1 to subcellular locations where it is needed, such as the phagosome in leukocytes.