Na+-Coupled Respiration and Reshaping of Extracellular Polysaccharide Layer Counteract Monensin-Induced Cation Permeability in Prevotella bryantii B14.

Monensin is an ionophore for monovalent cations, which is frequently used to prevent ketosis and to enhance performance in dairy cows. Studies have shown the rumen bacteria Prevotella bryantii B14 being less affected by monensin. The present study aimed to reveal more information about the respective molecular mechanisms in P.bryantii, as there is still a lack of knowledge about defense mechanisms against monensin. Cell growth experiments applying increasing concentrations of monensin and incubations up to 72 h were done. Harvested cells were used for label-free quantitative proteomics, enzyme activity measurements, quantification of intracellular sodium and extracellular glucose concentrations and fluorescence microscopy. Our findings confirmed an active cell growth and fermentation activity of P.bryantii B14 despite monensin concentrations up to 60 µM. An elevated abundance and activity of the Na+-translocating NADH:quinone oxidoreductase counteracted sodium influx caused by monensin. Cell membranes and extracellular polysaccharides were highly influenced by monensin indicated by a reduced number of outer membrane proteins, an increased number of certain glucoside hydrolases and an elevated concentration of extracellular glucose. Thus, a reconstruction of extracellular polysaccharides in P.bryantii in response to monensin is proposed, which is expected to have a negative impact on the substrate binding capacities of this rumen bacterium.

[Electrophysiological Effects of Ionophore-induced Increases in Intracellular Na+ in Cardiomyocytes].

Na ionophores increase intracellular Na+ ([Na+]i). Membrane potentials and currents were measured using microelectrode and whole-cell patch-clamp techniques. Monensin (10-6-3×10-5 M) reduced the slope of the pacemaker potentials and shortened the action potential duration (APD) in sino-atrial nodal and Purkinje cells. Monensin (10-5 M) shortened the APD and reduced the amplitude of the plateau phase in ventricular myocytes. Monensin decreased the hyperpolarization-activated inward current (If), and it increased the transient outward potassium current (Ito) in Purkinje cells. In addition, monensin decreased the sodium current (INa), shifting the inactivation curve to the hyperpolarized direction. Moreover, monensin decreased the L-type calcium current (ICa) in ventricular myocytes. The Na+-Ca2+ exchange current (INa-Ca) was augmented particularly in the reverse mode, and the Na+-K+ pump current (INa-K) was also activated by monensin in cardiomyocytes. The ATP-activated potassium current (IK,ATP) could be induced by monensin. Notably, the inward rectifying K+ current (IK1), and the slow delayed outward K+ current (IKs) were not affected evidently by monensin. Collectively, alteration of [Na+]i can influence the activities of various ion channels and transporters. Thus, the significance of altered [Na+]i should be taken into consideration in the action of drugs affecting [Na+]i such as digitalis, Na+ channel blockers, and Na+ channel activating agents.

Monensin-Induced Increase in Intracellular Na+ Induces Changes in Na+ and Ca2+ Currents and Regulates Na+-K+ and Na+-Ca2+ Transport in Cardiomyocytes.

BACKGROUND/AIMS: Monensin, an Na ionophore, increases intracellular Na ([Na]i). Alteration of [Na]i influences ion transport through the sarcolemmal membrane. So far, the effects of monensin on ventricular myocytes have not been examined in detail. The main objective of this study was to elucidate the mechanism via which monensin-evoked increases in [Na]i affect the membrane potential and currents in ventricular myocytes of guinea pigs. METHODS: Membrane potentials and currents were measured using the whole-cell patch-clamp technique in single myocytes. The concentration of intracellular Ca ([Ca]i) was evaluated by measuring fluorescence intensity of Fluo-4. RESULTS: Monensin (10-5M) shortened the action potential duration (APD) and reduced the amplitude of the plateau phase. In addition, monensin decreased the sodium current (INa) and shifted the inactivation curve to the hyperpolarized direction. Moreover, it decreased the L-type calcium current (ICa). However, this effect was attenuated by increasing the buffering capacity of [Ca]i. The Na-Ca exchange current (INa-Ca) was activated particularly in the reverse mode. Na-K pump current (INa-K) was also activated. Notably, the inward rectifying K current (IK1) was not affected, and the change in the delayed outward K current (IK) was not evident. CONCLUSION: These results suggest that the monensin-induced shortened APD and reduced amplitude of the plateau phase are primarily due to the decrease in the ICa, the activation of the reverse mode of INa-Ca, and the increased INa-K, and second due to the decreased INa. The IK and the IK1 may not be associated with the abovementioned changes induced by monensin. The elevation of [Na]i can exert multiple influences on electrophysiological phenomena in cardiac myocytes.

Sodium affects the sperm motility in the European eel.

The role of seminal plasma sodium and activation media sodium on sperm motility was examined by selectively removing the element from these two media, in European eel sperm. Sperm size (sperm head area) was also measured using an ASMA (Automated Sperm Morphometry Analyses) system, in the different conditions. Intracellular sodium [Na(+)]i was quantitatively analyzed by first time in the spermatozoa from a marine fish species. Measurement of [Na(+)]i was done before and after motility activation, by Flow Cytometry, using CoroNa Green AM as a dye. Sperm motility activation induced an increase in [Na(+)]i, from 96.72mM in quiescent stage to 152.21mM post-activation in seawater. A significant decrease in sperm head area was observed post-activation in seawater. There was a notable reduction in sperm motility when sodium was removed from the seminal plasma, but not when it was removed from the activation media. Sodium removal was also linked to a significant reduction in sperm head area in comparison to the controls. Our results indicate that the presence of the ion Na(+) in the seminal plasma (or in the extender medium) is necessary for the preservation of sperm motility in European eel, probably because it plays a role in maintaining an appropriate sperm cell volume in the quiescent stage of the spermatozoa.

Helical peptide-polyamine and -polyether conjugates as synthetic ionophores.

Two new synthetic ionophores in which the hydrophobic portion is represented by a short helical Aib-peptide (Aib=α-amino-isobutyric acid) and the hydrophilic one is a poly-amino (1a) or a polyether (1b) chain have been prepared. The two conjugates show a high ionophoric activity in phospholipid membranes being able to efficiently dissipate a pH gradient and, in the case of 1b, to transport Na(+) across the membrane. Bioactivity evaluation of the two conjugates shows that 1a has a moderate antimicrobial activity against a broad spectrum of microorganisms and it is able to permeabilize the inner and the outer membrane of Escherichia coli cells.

Effect of monensin withdrawal on rumen fermentation, methanogenesis and microbial populations in cattle.

This study was designed to obtain information on the residual influence of dietary monensin on ruminant fermentation, methanogenesis and bacterial population. Three ruminally cannulated crossbreed heifers (14 months old, 363 ± 11 kg) were fed Italian ryegrass straw and concentrate supplemented with monensin for 21 days before sampling. Rumen fluid samples were collected for analysis of short chain fatty acid (SCFA) profiles, monensin concentration, methanogens and rumen bacterial density. Post-feeding rumen fluid was also collected to determine in vitro gas production. Monensin was eliminated from the rumen fluid within 3 days. The composition of SCFA varied after elimination of monensin, while total production of SCFA was 1.78 times higher than on the first day. Methane production increased 7 days after monensin administration ceased, whereas hydrogen production decreased. The methanogens and rumen bacterial copy numbers were unaffected by the withdrawal of monensin.

Expression of interferon-γ in decidual natural killer cells from women with hypertensive disorder complicating pregnancy.

AIM: Hypertensive disorder complicating pregnancy (HDCP) is one of the most frequent and serious pregnancy-related diseases, which is closely related to disorders of the maternal immune system, especially the local immune microenvironment of the maternal-fetal interface. Uterine decidual natural killer (dNK) cells are the major immune cells in the maternal-fetal interface and they play an important role in establishing and maintaining a normal pregnancy. The aim of this study was to investigate the phenotype and function of dNK cells from women with HDCP. MATERIAL AND METHODS: Decidual tissues were collected from women with normal pregnancy (normal control group, n = 15 cases) and HDCP (HDCP group, n = 20 cases), respectively. The mononuclear cells were extracted from tissues and flow cytometry (FCM) was utilized to sort out dNK cells. The phenotypes of dNK cells (CD56(bright)CD16⁻CD3⁻ vs CD56(dim)CD16⁺CD3⁻) were detected by FCM. After being co-cultured with Phorbol 12-myristate 13-acetate, ionomycin and monensin, the expression level of interferon (IFN)-γ in the dNK cells was detected by FCM. RESULTS: The phenotypes of dNK cells from the two groups were dominated by the CD56(bright)CD16⁻CD3⁻ subset, with no significant statistical difference (P < 0.05). The expression level of IFN-γ in the dNK cells from women with HDCP was on a lower trend than those from women with normal pregnancy, having significant statistical difference (P = 0.000 < 0.05). CONCLUSIONS: Our results indicated that although the phenotype of dNK cells from women with HDCP is of no difference, their functions are abnormal. Impaired cell function leads to a lower expression level of IFN-γ and this may account for one of the pathogeneses of HDCP.

Stoichiometric relationship between Na(+) ions transported and glucose consumed in human erythrocytes: Bayesian analysis of (23)Na and (13)C NMR time course data.

We examined the response of Na(+),K(+)-ATPase (NKA) to monensin, a Na(+) ionophore, with and without ouabain, an NKA inhibitor, in suspensions of human erythrocytes (red blood cells). A combination of (13)C and (23)Na NMR methods allowed the recording of intra- and extracellular Na(+), and (13)C-labeled glucose time courses. The net influx of Na(+) and the consumption of glucose were measured with and without NKA inhibited by ouabain. A Bayesian analysis was used to determine probability distributions of the parameter values of a minimalist mathematical model of the kinetics involved, and then used to infer the rates of Na(+) transported and glucose consumed. It was estimated that the numerical relationship between the number of Na(+) ions transported by NKA per molecule of glucose consumed by a red blood cell was close to the ratio 6.0:1.0, agreeing with theoretical prediction.

Effect of cationic ionophore monensin on the lipid composition and fluidity of rat epididymal spermatozoal membrane.

The present study was aimed at exploring the effect of monensin, an antibiotic carboxylic polyether ionophore specific for Na(+), on the structural, chemical, and physiological changes of the epididymal sperm of Wistar rats. Animals received monensin at the dose of 3.5 mg/kg body weight daily orally for 70 days, a treatment duration that corresponds to the spermatogenic cycle in rats. At the end of the treatment regime, three regions of the epididymis were separated and the spermatozoa were collected. The plasma membranes of the spermatozoa were isolated and lipid composition, such total lipid, phospholipid, cholesterol, and ganglioside-sialic acid, was studied. Membrane dynamic behavior was investigated by lipid translational fluidity by pyrene excimer formation and rotational diffusion by diphenyl hexatriene polarization and anisotropy parameter. Structural changes in membrane were also evaluated by the dye-binding study with anilino naphthalene sulphonic acid. The results showed marked changes in lipid compositions, fluidity parameters, and kinetics of fluorescent dye binding in the epididymis, and it can be concluded that monensin, by interfering with normal physiological changes in spermatozoal maturation, may provide the basis of certain molecular intervention in the fertilizing capability of the epididymal spermatozoa and thereby may induce antifertility properties in male rats.

Functional expression, purification and reconstitution of the recombinant phosphate transporter Pho89 of Saccharomyces cerevisiae.

The Saccharomyces cerevisiae high-affinity phosphate transporter Pho89 is a member of the inorganic phosphate (Pi) transporter (PiT) family, and shares significant homology with the type III Na(+)/Pi symporters, hPit1 and hPit2. Currently, detailed biochemical and biophysical analyses of Pho89 to better understand its transport mechanisms are limited, owing to the lack of purified Pho89 in an active form. In the present study, we expressed functional Pho89 in the cell membrane of Pichia pastoris, solubilized it in Triton X-100 and foscholine-12, and purified it by immobilized nickel affinity chromatography combined with size exclusion chromatography. The protein eluted as an oligomer on the gel filtration column, and SDS/PAGE followed by western blotting analysis revealed that the protein appeared as bands of approximately 63, 140 and 520 kDa, corresponding to the monomeric, dimeric and oligomeric masses of the protein, respectively. Proteoliposomes containing purified and reconstituted Pho89 showed Na(+)-dependent Pi transport activity driven by an artificially imposed electrochemical Na(+) gradient. This implies that Pho89 operates as a symporter. Moreover, its activity is sensitive to the Na(+) ionophore monensin. To our knowledge, this study represents the first report on the functional reconstitution of a Pi-coupled PiT family member.

Quantitative model of NMR chemical shifts of 23Na+ induced by TmDOTP: applications in studies of Na+ transport in human erythrocytes.

The change in the NMR chemical shift of (23)Na(+) induced by the shift reagent TmDOTP was examined under various experimental conditions typical of cells, including changed Na(+), K(+), PO(4)(3-), and Ca(2+) concentrations, pH and temperature. A mathematical model was developed relating these factors to the observed chemical shift change relative to a capillary-sphere reference. This enabled cation concentrations to be deduced quantitatively from experimental chemical shifts, including those observed during biological time courses with cell suspensions containing TmDOTP DOTP, 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis (methylenephosphonate) [corrected]. The model was applied to a (23)Na NMR time course in which monensin, a sodium ionophore, was introduced to human erythrocytes, changing the concentration of cations which may bind TmDOTP, and also resulting in cell volume changes. Using the model with experimentally determined conditions, the chemical shift was predicted and closely followed the experimental values over time. In addition to the model, parameter fitting was achieved by calculating the likelihood distribution of parameters, and seeking the maximum likelihood with a Bayesian type of analysis.

A1Ao-ATP synthase of Methanobrevibacter ruminantium couples sodium ions for ATP synthesis under physiological conditions.

An unresolved question in the bioenergetics of methanogenic archaea is how the generation of proton-motive and sodium-motive forces during methane production is used to synthesize ATP by the membrane-bound A(1)A(o)-ATP synthase, with both proton- and sodium-coupled enzymes being reported in methanogens. To address this question, we investigated the biochemical characteristics of the A(1)A(o)-ATP synthase (MbbrA(1)A(o)) of Methanobrevibacter ruminantium M1, a predominant methanogen in the rumen. Growth of M. ruminantium M1 was inhibited by protonophores and sodium ionophores, demonstrating that both ion gradients were essential for growth. To study the role of these ions in ATP synthesis, the ahaHIKECFABD operon encoding the MbbrA(1)A(o) was expressed in Escherichia coli strain DK8 (Δatp) and purified yielding a 9-subunit protein with an SDS-stable c oligomer. Analysis of the c subunit amino acid sequence revealed that it consisted of four transmembrane helices, and each hairpin displayed a complete Na(+)-binding signature made up of identical amino acid residues. The purified MbbrA(1)A(o) was stimulated by sodium ions, and Na(+) provided pH-dependent protection against inhibition by dicyclohexylcarbodiimide but not tributyltin chloride. ATP synthesis in inverted membrane vesicles lacking sodium ions was driven by a membrane potential that was sensitive to cyanide m-chlorophenylhydrazone but not to monensin. ATP synthesis could not be driven by a chemical gradient of sodium ions unless a membrane potential was imposed. ATP synthesis under these conditions was sensitive to monensin but not cyanide m-chlorophenylhydrazone. These data suggest that the M. ruminantium M1 A(1)A(o)-ATP synthase exhibits all the properties of a sodium-coupled enzyme, but it is also able to use protons to drive ATP synthesis under conditions that favor proton coupling, such as low pH and low levels of sodium ions.

Phospholipase C-η2 is activated by elevated intracellular Ca(2+) levels.

Phospholipase C-η2 (PLCη2) is a novel enzyme whose activity in a cellular context is largely uncharacterised. In this study the activity of PLCη2 was examined via [(3)H]inositol phosphate release in COS7 cells expressing the enzyme. PLCη2 activity increased approximately 5-fold in response to monensin, a Na(+)/H(+) antiporter. This was significantly inhibited by CGP-37157 which implies that the effect of monensin was due, at least in part, to mitochondrial Na(+)/Ca(2+)-exchange. Direct activation of PLCη2 by <1µM Ca(2+) was confirmed in permeabilised transfected cells. The roles of the PH and C2 domains in controlling PLCη2 activity via membrane association were also investigated. A PH domain-lacking mutant exhibited no detectable activity in response to monensin or Ca(2+) due to an inability to associate with the cell membrane. Within the C2 domain, mutation of D920 to alanine at the predicted Ca(2+)-binding site dramatically reduced enzyme activity highlighting an important regulatory role for this domain. Mutation of D861 to asparagine also influenced activity, most likely due to altered lipid selectivity. Of the C2 mutations investigated, none altered sensitivity to Ca(2+). This suggests that the C2 domain is not responsible for Ca(2+) activation. Collectively, this work highlights an important new component of the Ca(2+) signalling toolkit and given its sensitivity to Ca(2+), this enzyme is likely to facilitate the amplification of intracellular Ca(2+) transients and/or crosstalk between Ca(2+)-storing compartments in vivo.