Effect Of pH Changes Research Articles

The effects of pH change on Ca++ signaling and force in pregnant human myometrium

Objective: This study was designed to determine the effects of both intracellular and extracellular pH change on contractile activity and intracellular Ca++ during spontaneous contractions, oxytocin, and depolarization-induced stimulation of human myometrium. Study Design: Human myometrial tissue was obtained at elective caesarean delivery at term (37-41 completed weeks of gestation). Longitudinal strips were dissected and loaded with the calcium sensitive indicator Indo-1. Statistical significance was tested with the Student t test. Results: Both intracellular and extracellular acidification significantly reduces or even abolishes phasic activity, whether it arises spontaneously or in the presence of oxytocin. These contractile changes can be accounted for by the changes in intracellular Ca++. Alkalinization produced the opposite effects. However, baseline or maintained tension changes could not be accounted for by changes in intracellular Ca++. Conclusion: We suggest that the effects on phasic activity are due to the inhibition of L-type calcium entry and that, during maintained or baseline activity, pH-sensitive Ca++ release, possibly from the sarcoplasmic reticulum occurs; but it is insufficient to overcome the inhibitory effects at the myofilaments. We conclude that alterations of pH significantly affect calcium signaling and force production in the human myometrium and may contribute to dysfunction in labor. (Am J Obstet Gynecol 2003;188:1031-8.)

Lability of Cd, Cu, and Zn in polluted soils treated with lime, beringite, and red mud and identification of a non-labile colloidal fraction of metals using istopic techniques.

The use of soil amendments has been proposed as a low input alternative for the remediation of metal polluted soils. However, little information is available concerning the stability, and therefore the longevity, of the remediation treatments when important soil parameters change. In this paper we investigate the effect of pH changes on the lability of heavy metals in soils treated with lime, beringite, and red mud using a modified isotopic dilution technique in combination with a stepwise acidification procedure. Significant amounts of nonlabile (fixed) Cu and Zn were found to be associated with colloids <0.2 microm in the solution phase. The results obtained indicated that the mobility of fixed colloidal metals is significant and increases with soil pH. This must be considered because most of the soil amendments are alkaline and increase soil pH. All the soil amendments significantly decreased the lability of Cd, Zn, and Cu in the soils as a whole. However, when the soils were re-acidified, the labile pool of metals increased sharply and in the case of lime and beringite, the lability of the metals was similar, at equal pH, to the untreated soil. In contrast the lability of metals in the red mud treated soils was always smaller than that in the untreated soils across the range of pH values tested. These results suggest that the mechanism of action of lime and beringite is similar and probably related to increased metal adsorption and precipitation of metal hydroxides and carbonates at high pH. In the case of red mud, a combination of pH dependent and independent mechanisms (possibly solid-phase diffusion or migration into micropores) may be responsible for the metal fixation observed.

The combined effects of hardness, pH, and dissolved organic carbon on the chronic toxicity of Zn to D. magna: development of a surface response model.

The effect of changes in pH, hardness, and dissolved organic carbon (DOC) and the possible interactions among these parameters on the chronic toxicity of zinc to D. magna were investigated. Based on a Central Composite Design, models were developed that can explain the observed variation in EC(10) and EC(50) as a function of these toxicity modifying factors. All three parameters significantly altered the observed effect concentrations based on net reproductive rate. The largest differences in 21-day EC(10)s and EC(50)s caused by these factors were 10.1 and 4.9, respectively. An increase in pH and/or DOC decreased zinc toxicity. The significant interaction between pH and DOC on observed chronic Zn toxicity is in accordance with earlier reported increased sorption efficiency of Zn to humic substances at higher pH levels. Lowest Zn toxicity was observed in tests performed with moderately hard test media (between 200 and 300 mg/L as CaCO(3)). Lower or higher hardness of the test medium resulted in lower effect concentrations. Based on physico-chemical characteristics of the test media, developed models can be used to explain the variation between reported NOECs for Zn and may improve current environmental risk assessment procedures of metals.

Mechanisms of flux decline during ultrafiltration of dairy products and influence of pH on flux rates of whey and buttermilk

The flux pattern during the ultrafiltration (UF) of milk systems (whole milk, skim milk and butter milk) was quite different to sweet or acid whey. With whey, the initial flux was higher, but it fell with time as a result of membrane fouling. Milk systems gave a lower initial flux, but flux remained unaltered during processing despite an increase in the fouling coefficient. The higher concentration of protein in the milk systems seems to promote concentration polarization which controls permeate flux. The flux pattern for sweet whey and buttermilk was strongly influenced by pH. Increasing the pH of buttermilk from 6.6 up to 8.0 tended to reduce initial flux values and reduced deposit formation. Buttermilk flux at high pH range (6.6 and above) was mostly controlled by concentration polarization. Reducing the pH below 6.0 increased the initial flux, but caused more deposit on the membrane. Almost the opposite was noticed in sweet whey. The initial flux increased as pH increased, followed by considerable flux decline during 1-h period of operation, which is linked to greater fouling of the membrane. Reducing the pH significantly reduced initial flux, but deposit formation was at lower levels. These changes are brought about by the effect of pH change on proteins and minerals of milk and whey.

The effect of intracellular alkalinisation on intracellular Ca(2+) homeostasis in a human chondrocyte cell line.

Intracellular pH (pH(i)) is a well-established determinant of cartilage matrix metabolism. Changes to chondrocyte pH(i), and therefore matrix turnover rates, arise following joint loading. It is not yet clear whether pH changes exert their effects on matrix metabolism directly, or by changing the concentration of another, as yet unidentified, intracellular factor. In this study the effect of intracellular alkalinisation on intracellular [Ca(2+)] has been examined using the human chondrocyte C-20/A4 cell line. pH(i) was manipulated by the addition of weak bases to suspensions of chondrocytes and fluorimetric techniques were employed to measure pH(i) and [Ca(2+)](i). The effect of pH(i) changes on intracellular inositol 1,4,5-trisphosphate (IP(3)) levels was also determined. The pH-sensitive properties of the Ca(2+)-sensitive fluoroprobe employed in this study, Fura-2, were investigated such that artefactual effects of pH changes upon the dye could be discounted. It was demonstrated that, for dye loaded into cells, alkalinisation resulted in a small increase in the affinity of the dye for Ca(2+) ions. Intracellular alkalinisation elicited by treatment with either of the weak bases trimethylamine or ammonium chloride initiated a rise in [Ca(2+)](i). This effect was too large to be explicable by the effects of pH changes on Fura-2 and was not dependent on the presence of extracellular Ca(2+) ions. Prior depletion of intracellular Ca(2+) stores by treatment with thapsigargin inhibited alkalinisation-induced increases in [Ca(2+)](i) and intracellular alkalinisation was also associated with increased levels of intracellular IP(3). These results confirm that alkaline pH(i) changes associated with dynamic loading of cartilage also result in knock-on alterations to [Ca(2+)](i). Given the sensitivity of cartilage matrix metabolism to [Ca(2+)](i) it is likely that this signalling cascade forms an important part of the mechanotransduction pathway that determines the response of chondrocytes to applied load.

Steady-State Fluorescence Investigation of Pyrene-Labeled Poly(Acrylic Acid)s in Aqueous Solution and in the Presence of Sodium Dodecyl Sulfate

Commercial poly(acrylic acid) (PAA) samples with Mv = 150 000 and 450 000 were labeled randomly with small amounts (2−3 mol %) of 1-pyrenylmethyl (MePy) groups. A sample of PAA (Mv = 450 000) labeled with 2 mol % MePy and modified with 2 mol % n-dodecyl (C12) groups was also prepared. The photophysical properties of the polymers have been investigated by steady-state fluorescence spectroscopy. The ratio (IE/IM) of excimer-to-monomer emission intensities was used to determine the effect of changes in pH and addition of sodium dodecyl sulfate (SDS) on the solution properties of the labeled polymers in the absence and presence of salt (NaCl). Changes in polymer conformation in aqueous solution upon addition of base were revealed by the curve IE/IM vs pH that had an inflection point at pH 4.7, the pKa value of labeled PAA. The ratio I1/I3 of the emission of MePy linked to PAA was monitored to obtain information on the micropolarity sensed by the pyrene label and how it is affected by external stimuli such as changes in pH and addition of surfactant. SDS interacts with labeled PAA in solution of pH 3 to form a polymer/SDS complex with a critical aggregation concentration (CAC) lower than the critical micelle concentration of SDS. The CAC values decrease further in the presence of NaCl but are not affected significantly by the molecular weight of the parent PAA or the grafted dodecyl along the PAA chain.

Reducing the interference from CO 2 or organic acids in ion-selective polymer membrane sensors having a field-effect transistor as internal reference element

Changes in sample concentrations of CO 2 or organic acids cause potential instabilities when polymer membranes are directly applied to the surface of ion-selective field-effect transistors (ISFETs). Currently used designs avoid this well-documented effect by placing a layer of aqueous buffer between polymeric membrane and ISFET serving as internal reference element. Here, we propose another solution to the problem. In order to compensate for the effect of pH changes on the ISFET threshold voltage, a double membrane is applied whose inner layer is pH-sensitive, while the outer layer exposed to the sample is a conventional ion-selective membrane. It is shown that this approach strongly reduces the earlier-mentioned interference effects.

Molecular mechanisms of cardiac myofilament activation: modulation by pH and a troponin T mutant R92Q.

Activation of cardiac myofilaments is a complex process involving steric, allosteric, and cooperative mechanisms. The complexity of the protein-protein interactions that result in the rise and fall of tension in the heartbeat provide many points that may be modified by various control mechanisms. These include modulation by the sarcomere length, covalent modulation by protein phosphorylation and non-covalent modulation by the chemical environment surrounding the myofilaments. We focus here on effects of pH change in the context of one of the mutations in cardiac troponin T (R92Q) that causes familial hypertrophic cardiomyopathy (FHC). We tested whether this change in charge would manifest itself functionally by a difference in the pCa-force relations of skinned fiber bundles activated at pH values of 6.5, 7.0 and 7.5. Fiber bundles containing the cTnT-R92Q mutant demonstrated an increase in sensitivity to Ca2+ at all three pH values. However, the relative magnitude of the increase in Ca2+-sensitivity induced by the mutant cTnT increased as the pH was decreased from pH 7.5 to pH 7.0 and to pH 6.5. Maximum force generated by the myofilaments fell as pH was lowered over this range, but the percent fall in maximum force was the same for fiber bundles containing wild-type and mutant cTnT. Our results indicate that ischemia that may be associated with FHC may exacerbate the functional changes induced by the cTnT mutation.

PH and rate of "dark" events in toad retinal rods: test of a hypothesis on the molecular origin of photoreceptor noise.

Thermal activation of the visual pigment constitutes a fundamental constraint on visual sensitivity. Its electrical correlate in the membrane current of dark-adapted rods are randomly occurring discrete "dark events" indistinguishable from responses to single photons. It has been proposed that thermal activation occurs in a small subpopulation of rhodopsin molecules where the Schiff base linking the chromophore to the protein part is unprotonated. On this hypothesis, rates of thermal activation should increase strongly with rising pH. The hypothesis has been tested by measuring the effect of pH changes on the frequency of discrete dark events in red rods of the common toad Bufo bufo. Dark noise was recorded from isolated rods using the suction pipette technique. Changes in cytoplasmic pH upon manipulations of extracellular pH were quantified by measuring, using fast single-cell microspectrophotometry, the pH-dependent metarhodopsin I-metarhodopsin II equilibrium and subsequent metarhodopsin III formation. These measurements show that, in the conditions of the electrophysiological experiments, changing perfusion pH from 6.5 to 9.3 resulted in a cytoplasmic pH shift from 7.6 to 8.5 that was readily sensed by the rhodopsin. This shift, which implies an 8-fold decrease in cytoplasmic [H(+)], did not increase the rate of dark events. The results contradict the hypothesis that thermal pigment activation depends on prior deprotonation of the Schiff base.

Electrospray mass spectrometric studies of L-carnosine (beta-alanyl-L-histidine) complexes with copper(II) or zinc ions in aqueous solution.

Electrospray ionization mass spectrometry (ESI-MS) was used for the speciation of supramolecular assemblies formed between equimolar amounts of carnosine and copper or zinc ions in dilute aqueous solutions. In the case of pure carnosine and carnosine/copper systems, the effect of pH changes, in the range 2-9, on the complexes surviving in solution was also explored. ESI data, besides supporting previous reported results on the formation of dimeric carnosine/copper and carnosine/zinc complexes, allowed a more complete speciation of the examined systems, bringing to light the existence of bis-complex species and, in the zinc case, the formation of oligomeric species. The data obtained for the systems investigated show that ESI-MS is not only a reliable and fast technique for the analysis of the metal/ligand systems, but also an interesting tool to obtain stoichiometric information on metal complexes formed in very low concentration solutions.

Effect of pH changes on reactivity of rat mesenteric artery segments at different magnitude of stretch.

The reaction to noradrenaline (NA) (10 microM) and electrical field stimulation (EFS) was studied in rat mesenteric artery segments at different magnitude of stretch and the solution pH. Alkaline solution (pH 7.8) potentiated and acidic solution (pH 7.0 or 6.6) inhibited the EFS-evoked response of segments stretched to values corresponding to arterial pressure of 5-200 mmHg. These pH changes failed to alter resting tension at any magnitude of stretch. Acedic solution of pH 6.6 caused 2-fold decrease in noradrenaline- and 5-15-fold decrease in the EFS-evoked response of segments stretched to values corresponding to arterial pressure of 50, 125, and 200 mmHg. In segments pre-contracted with noradrenaline (10 microM) acidification caused the decrease of the dilation and appearance of the constriction induced by the EFS. The effect of acidosis on the EFS-evoked response was diminished and the effect on noradrenaline-evoked response was abolished in the presence of nitric oxide synthase blocker, NG-nitro-L-arginine (100 microM). These results suggest that acidosis effectively impairs reactivity of the rat mesenteric artery in a wide range of its stretch, and the inhibition of the response to noradrenaline occurs completely, while to EFS only partially due to nitric oxide (NO) release, presumably by the endothelium. In addition, it was shown that acidosis is able to act not only as the commonly known dilator agent, but also as an agent potentiating constriction in case of the high noradrenaline-induced tone.

The effect of pH change on the gastric emptying of liquids measured by electrical impedance tomography and pH-sensitive radiotelemetry capsule

Citrate phosphate buffer liquid adjusted to different pH values was used to investigate the gastric emptying profiles in human using simultaneous monitoring by electrical impedance tomography (EIT) and pH sensitive radiotelemetry capsule. No interference was observed between the two methods during data acquisition periods. A positive correlation between methods from the pooled data was demonstrated. Statistical moments analysis demonstrated a significant delay in the onset of gastric emptying and also the mean gastric residence time of the pH 3 buffer liquid (34.7–46.7 min) when compared with pH 7 buffer liquid (14.4–22.5 min). These data suggest that the negative feedback gastrin related response to acidity of the liquid was high. However, incorporation of an acid suppression compound (ranitidine), as part of the control study showed that the EIT imaging of this buffer could be successfully performed under normal physiological conditions. When 450 ml pH 7 buffer liquid was measured, no significant difference in gastric emptying rate was observed. This study demonstrated that, citrate phosphate buffers can be used as an alternative test liquid for EIT monitoring, and that pH has a systematic effect on gastric emptying and the lag phase.

Effect of changes in pH on the release of flavour compounds from a soft drink-related model system

Abstract Citric acid and phosphoric acid were added in variable amounts to a soft drink model system to show their effect on the release of six flavour compounds. High concentrations of the acids decreased the release of esters, probably because of the presence of large amounts of the dissociated form of the acids. However, the same amounts of added citric acid had no effect on flavour release when pH was regulated with sodium hydroxide. Changes in pH values achieved by adding hydrochloric acid also had no effect on flavour release. These results indicate that pH values used in soft drinks do not affect the release of flavour molecules. It is more likely the citric acid and the phosphoric acid, particularly their dissociated forms, which decrease the release of the esters. The other flavour compounds were not affected.

PH influence on sorption characteristics of heavy metal in the vadose zone

Sorption is an important process in the modelling and prediction of the movement of heavy metals in unsaturated clay barriers. This experimental study investigates the effect of pH changes in the acidic range on the sorption characteristics of heavy metals such as: lead, copper and zinc in an unsaturated soil. A series of one-dimensional coupled solute and moisture leaching column tests, using different heavy metal solutions, were conducted on an unsaturated illitic soil at varying pH values. Variations of volumetric water content (VWC) with distance were measured for different time durations, and concentrations of heavy metals in the liquid and solid phases were analysed. Partitioning coefficient profiles of contaminants along the soil column were determined for each individual layer in the soil. Results from column leaching tests showed that the sorption characteristics of heavy metals are controlled by many factors which should be taken into consideration, i.e. the VWC, time of wetting, soil pH, and the influent heavy metal concentrations. Simplification of K d as a constant and of the VWC as a linear function cannot be considered a good assumption and may lead to an improper evaluation of the sorption phenomena and also to serious errors in predicting contaminant transport through unsaturated soils.

Involvement of cholinergic mechanisms in the central control of respiration in the cane toad, Bufo marinus

Chemical substrates, central sites and central mechanisms underlying the regulation of breathing in lower vertebrates have not been well characterized. The present study was undertaken to determine the effect of pH changes and cholinergic agents on the central control of respiration in the cane toad, Bufo marinus. Adult toads were anesthetized, catheterized and unidirectionally ventilated before exposing the brainstem. An airtight buccal cannula was also inserted through the tympanum to record buccal pressure. The animal was decerebrated, anesthetic removed and the responses to pH changes of solutions bathing the ventral surface of the medulla (VSM) were tested by superfusing the VSM with mock cerebrospinal fluid (mCSF) of pH 7.8-normal, 7.2-acidic and 8.4-basic. The acidic solution increased respiratory activity, the basic solution decreased activity and the normal solution had no effect. In addition, cholinergeric agents (acetylcholine-ACh, physostigmine-Phy, nicotine-Nic, and atropine-Atr) dissolved in mCSF were applied bilaterally onto the VSM using filter paper pledgets. ACh, Phy and Nic increased episodic breathing frequency by 14.3±9.7, 9.4±5.4 and 29.1±11.8 %, respectively, whereas, Atr caused a decrease (−26.6±16.6%). These agents had no effect on blood pressure. It is therefore, concluded that the VSM is pH sensitive and a cholinergic mechanism is involved in the central modulation of respiration in Bufo.

A Pre- and Post-Denitrification System Treating a Very High Ammonia Landfill Leachate: Effects of pH Change on Process Performance

The prime objective of this research was to investigate the nitrogen removal capabilities of a pre- and post-denitrification process, when treating landfill leachate containing an ammonia concentration of over 2200 mg N l−1. The treatment system, also known as a 4-Stage Bardenpho process, was operated with an external recycle ratio of 3:1 and an internal recycle ratio of 4:1. The first anoxic reactor actual hydraulic retention time was 1.5 hours, while the first aerobic retention time was 3 hours. The very high ammonia concentration was simulated by pumping ammonium chloride into the first anoxic reactor of the system. Methanol was used as the organic carbon source for denitrification. At an influent ammonia concentration of about 2200 mg N l−1, the anoxic pH levels stabilized at about 8.6 within the first reactor, and at about 9.8 within the second reactor. These high anoxic pH levels were partially responsible for decreased denitrification and, hence, residual NOx concentrations in the effluent. By decreasing the pH in the anoxic basins, the overall performance of the system immediately improved; the effluent NOx concentration decreased rapidly over a period of about six days, from an average 80 mg N l−1 to about 60 mg N l−1, with some samples as low as 40 mg N l−1. Subsequently, increased leachate toxicity resulted in an unexpected system failure; although the treatment system eventually recovered and stabilized, denitrification in each anoxic reactor remained at only about 55%, with final effluent NOx concentrations of over 100 mg N l−1. Despite this reduced level of performance, the decrease in anoxic pH resulted in enhanced nitrification performance, complete ammonia removal in the first aerobic reactor, and a more stable, overall performance in the 4-Stage Bardenpho process.

A comparative study of the effect of pH and inorganic carbon resources on the photosynthesis of three floating macroalgae species of a Mediterranean coastal lagoon.

This study examines the effect of pH changes on photosynthetic characteristics and the role of dissolved inorganic carbon (DIC) in determining the dominance of three species of macroalgae Chaetomorpha linum (O.F. Müller) Kützing, Gracilaria verrucosa (Hudson) Papenfuss and Ulva sp. in a Mediterranean coastal lagoon. Fluctuations of pH were measured in the lagoon in summer. Water column CO(2) and HCO(3)(-) concentrations inside the algal mat showed significant diurnal fluctuations, from a morning peak to an afternoon low, decreasing 96 and 40%, respectively. The response of photosynthesis to increased pH was examined in laboratory conditions in spring (May) and summer (July). The photosynthetic rate declined rapidly at pH above 8.5 and below 6.5. G. verrucosa responded differently in spring and summer showing acclimation to higher pH in summer than in spring. In Ulva sp. incubations, we observed optimum photosynthesis between pH 6 and 7.5. The decrease in photosynthetic rate below pH 6 was lower (12.30%) than above pH 8 (81.03%). This difference may be related to the origin of the macroalgae, suggesting acclimation to the original pH of the environment. Results from instantaneous photosynthesis measurements indicate that low DIC-availability limits the photosynthetic capacity of G. verrucosa, C. linum and Ulva sp. in spring and of C. linum at high irradiances in summer. Our results also show that G. verrucosa has a higher efficiency at low CO(2) concentrations than C. linum and Ulva sp. It is suggested that G. verrucosa may be better adapted to maintain higher photosynthetic rates than other macroalgae in conditions of tissue N sufficiency and low water DIC concentrations which are typical of shallow coastal environments in summer.

Modeling of arsenic rejection considering affinity and steric hindrance effect in nanofiltration membranes

Rejection characteristics of arsenic compounds such as arsenite, dimethyl arsinic acid, and arsenate were examined regarding the effect of pH change in nanofiltration. Rejection mechanism of arsenic compounds was explained by comparing experimental rejection with calculation of the Extended Nernst-Planck model coupled with steric hindrance model. Nanofiltration membranes of the same material show similar rejection characteristics of arsenic compounds in different species. Steric hindrance and electrostatic effect in the nanofiltration membranes was well described by the model because the rejection of chloride, sulfate and arsenate ions, which exist in ionized forms at a wide pH range showed quite good agreement between model calculation and experimental result. The rejection of dimethyl arsenic acid and arsenite required the consideration of mutual interaction between membrane material and solutes as well as steric hindrance and electrostatic effect. A system with ultra low-pressure nanofiltration membrane coupled with pre-oxidation device was suggested for the treatment of arsenic in groundwater in Bangladesh.

Investigations on the behaviour of acidic, basic and neutral compounds in capillary electrochromatography on a mixed-mode stationary phase

This work describes the separation of acidic, basic and neutral organic compounds as well as inorganic anions in a single run by capillary electrochromatography employing a stationary phase which exhibits both strong anion-exchange and reversed-phase chromatographic characteristics. The positive surface charge of this stationary phase provided a substantial anodic electroosmotic flow. The analytes were separated by a mixed-mode mechanism which comprised chromatographic interactions (hydrophobic interactions, ion-exchange) as well as electrophoretic migration. The influence of ion-exchange and hydrophobic interactions on the retention/migration of the analytes could be manipulated by varying the concentration of a competing ion and/or the amount of organic modifier present in the background electrolyte. Additionally the effects of pH changes on both the chromatographic interactions as well as the electrophoretic migration of the analytes were investigated.

Inhibition of the human intermediate-conductance, Ca2+-activated K+ channel by intracellular acidification.

The effect of changes in pH on the gating properties of the cloned human intermediate-conductance, Ca2+-activated K+ channel (hIK) was studied using the patch-clamp technique. Multi-channel inside-out recordings of patches from HEK-293 cells stably expressing hIK channels revealed that the channel activity is modulated by changes in intracellular pH (pHi). Changes in extracellular pH (pHo) in the range from pH 6.0 to 8.2 did not affect the hIK whole-cell current. Intracellular acidification gradually decreased the activity of the hIK channel, approaching zero activity at pHi 6.0. Decreasing pHi altered neither the conductance nor the inward rectification of hIK channels. The proton-induced inhibition of the multi-channel hIK patch current could not be counteracted by increasing the cytosolic Ca2+ concentration to 30 microM. The molecular sensory mechanism underlying the proton-induced modulation of hIK gating is at present unknown.