mM For Ca Research Articles

Bilayer cellulosic FO membrane developed by polydopamine and nanochitosan through layer by layer coating process

A highly efficient bilayer cellulose acetate forward osmosis (FO) membrane was developed using polydopamine (PDA) and chitosan nanoparticles (CsNP) through layer by layer coating process and characterized using DLS, FESEM, AFM, EDX, and static contact angle. The use of CsNP and PDA led to an improvement in chemical properties, surface hydrophilicity, and structural parameter. The experimental tests for both RO and FO experiments were carried out to calculate structural parameter (it decreased from 0.59 mm for neat CA to 0.37 mm for CA-PDA/CsNP2) of membranes. Also, the salt rejection and water permeability of membranes were tested in RO mode using 40 mM NaCl, while the water flux and reverse salt flux of membranes were analyzed in FO test. The CA-PDA/CsNP2 membrane with 0.6 wt.% of CsNP in the coating solution not only showed a high water permeation flux about 21.23 LMH for 2 mM NaCl but also decreased its reverse salt flux from 7.08 to 4.52 gMH. According to the fouling test results, the normalized water flux of the neat membrane declined from 1 to about 0.65 while it was higher than 0.85 for CA-PDA/CsNP2 which represents an improvement in the antifouling property. This improvement was mainly due to an increase in the hydrophilicity of the coated membrane and the electrostatic repulsion among the foulant and surface of CA-PDA/CsNP2. The results showed that the fabricated CA-PDA/CsNP2 membrane shows a high potential application in the FO process and is more competitive than other existing FO membranes.

Experimental study on the effects of calcium-based additives to control ammonium bisulfate and ash mixture deposition with an on-line digital image technique

The Ash deposition caused by ammonium bisulfate (NH4HSO4, ABS) and fly ash blocks and corrodes air preheaters in coal-fired power plants, affecting heat transfer efficiency and boiler operation safety. In this work, the effects of three calcium-based additives (Ca(OH)2, CaO, and CaCO3) on ash deposition were studied, and the effect of the molar ratio of Ca(OH)2 to ABS was studied. A probe was applied to accumulate ash deposition while an on-line digital image technique was used to record the morphology of ash throughout its deposition. New research ideas and methods were used in this work. The results showed that all calcium-based additives could inhibit the deposition of ash, among which the effect of Ca(OH)2 was the best, and as the molar ratio was increased, the thickness of ash deposition decreased. These results were observed because although ABS was sticky and easily adsorbed fly ash, causing ash deposition, additives reacted with ABS to reduce its content, thereby reducing the ash deposition. As the molar ratio was increased, the amount of ABS further reduced, leading to less ash deposition. When the molar ratio of additives to ABS was 2:1, the maximum thicknesses of ash deposition were 0 mm, 0.81 mm and 1.24 mm for Ca(OH)2, CaO and CaCO3, respectively; however, the maximum thickness of ash deposition was 2.37 mm without additives. Using Ca(OH)2 as an additive, the maximum thicknesses of ash deposition were 1.43 mm, 1.22 mm, and 0 mm at molar ratios of 0.5:1, 1:1, and 2:1, respectively. For a better understanding of ash deposition, the deposition was tested by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectrometry (EDS). This work provided reliable suggestions on the choice of additives to reduce ash deposition in coal-fired power plants.

Evaluation of preoperative ultrasonographic and biochemical features of patients with aggressive parathyroid disease: is there a reliable predictive marker?

Parathyroid cancer (PC) represents < 1% of cases of PHPT. Tumors demonstrating atypical histopathologic features and don't fulfill criteria for carcinoma are classified as atypical adenomas (APA). The purpose of this study was to determine a biochemical or ultrasonographic feature that can predict aggressive disease requiring more extensive surgery and closer follow-up. Twenty eight patients operated for PHPT and diagnosed with atypical adenoma (23 patients) or carcinoma (5 patients) were enrolled in this study. The control group consisted of 102 patients operated between the same dates and diagnosed with classical PA. Classical adenomas, atypical adenomas, and carcinomas were compared according to their biochemical and ultrasonographic parameters. Serum Ca levels were significantly higher in the PC group compared with the APA and classical PA groups. Serum median PTH, Serum ALP and UCa was significantly higher in the APA and carcinoma groups compared to the classical PA group. ROC analysis was made to determine the best cut off values for predicting aggressive disease were 12.45 mg/dL, 265.05 pg/mL, 154.5 IU/l, 348.5 mg/day and 21.5 mm for Ca, PTH, ALP, UCa and the adenoma diameter, respectively. Multivariate analysis showed that serum Ca, ALP and isoechoic/cystic appearance were independent predictors for aggressive disease. Preoperatively high PTH, ALP, and UCa levels and large lesions with isoechoic or cystic appearances may be predictive of atypical adenoma or carcinoma in patients being evaluated for PHPT. In such cases, surgeons may prefer en bloc parathyroidectomy to minimally invasive surgery.

Effect of alginate on the aggregation kinetics of copper oxide nanoparticles (CuO NPs): bridging interaction and hetero-aggregation induced by Ca(2.).

The stability of CuO nanoparticles (NPs) is expected to play a key role in the environmental risk assessment of nanotoxicity in aquatic systems. In this study, the effect of alginate (model polysaccharides) on the stability of CuO NPs in various environmentally relevant ionic strength conditions was investigated by using time-resolved dynamic light scattering. Significant aggregation of CuO NPs was observed in the presence of both monovalent and divalent cations. The critical coagulation concentrations (CCC) were 54.5 and 2.9mM for NaNO3 and Ca(NO3)2, respectively. The presence of alginate slowed nano-CuO aggregation rates over the entire NaNO3 concentration range due to the combined electrostatic and steric effect. High concentrations of Ca(2+) (>6mM) resulted in stronger adsorption of alginate onto CuO NPs; however, enhanced aggregation of CuO NPs occurred simultaneously under the same conditions. Spectroscopic analysis revealed that the bridging interaction of alginate with Ca(2+) might be an important mechanism for the enhanced aggregation. Furthermore, significant coagulation of the alginate molecules was observed in solutions of high Ca(2+) concentrations, indicating a hetero-aggregation mechanism between the alginate-covered CuO NPs and the unabsorbed alginate. These results suggested a different aggregation mechanism of NPs might co-exist in aqueous systems enriched with natural organic matter, which should be taken into consideration in future studies. Graphical abstract Hetero-aggregation mechanism of CuO nanoparticles and alginate under high concentration of Ca(2.)

Evaluation of particle size distributions produced during ultra-violet nanosecond laser ablation and their relative contributions to ion densities in the inductively coupled plasma

Relative contributions to ion densities in the inductively coupled plasma (ICP) of particles of various sizes produced by laser ablation (LA) were investigated. Particles generated by 266nm, ns LA of BaF2, CaF2, and a scandium aluminum alloy, characterized using SEM, consisted of hard and soft agglomerates, spherical particles, and irregularly-shaped particles. Although soft agglomerates and spherical particles were common to aerosols generated by LA in all cases, hard agglomerates appeared to be unique to the scandium aluminum alloy, while irregularly-shaped exfoliated particles were unique to the calcium and barium fluoride windows. The spatial distributions of Ca, Ba, and Sc ions in the ICP were determined from laser-induced fluorescence images taken with filters of pore sizes from 1–8μm added in-line to the transport tube upstream from the ICP. In all cases, a significant fraction of the ions formed in the ICP originated from micron-sized particles. Differences in the penetration depths of nanometer-sized agglomerates and micron-sized particles were about 2mm for Ca and 1mm for Ba. Differences in the penetration depths of nanometer and micron-sized agglomerates observed in the case of aluminum scandium were much less significant. This suggests that micron-sized hard-agglomerates and nanometer-sized soft-agglomerates experience very similar vaporization patterns. Additionally, there was evidence that flow patterns in the transport tube affect the trajectories of particles entering the plasma.

ICP-OES: Why spectral lines are true peaks and how this can fool the user.

ICP-OES: Why spectral lines are true peaks and how this can fool the user.

Aggregation Kinetics of Manganese Dioxide Colloids in Aqueous Solution: Influence of Humic Substances and Biomacromolecules

In this work, the early stage aggregation kinetics of manganese dioxide (MnO2) colloids in aqueous solution and the effects of constituents of natural organic matter (i.e., Suwannee River fulvic acid (SRFA), Suwannee River humic acid (SRHA), alginate, and bovine serum albumin (BSA)) were investigated by time-resolved dynamic light scattering. MnO2 colloids were significantly aggregated in the presence of monovalent and divalent cations. The critical coagulation concentrations were 28, 0.8, and 0.45 mM for NaNO3, Mg(NO3)2, and Ca(NO3)2, respectively. The Hamaker constant of MnO2 colloids in aqueous solution was 7.84 × 10(-20) J. All the macromolecules tested slowed MnO2 colloidal aggregation rates greatly. The steric repulsive forces, originated from organic layers adsorbed on MnO2 colloidal surfaces, may be mainly responsible for their stabilizing effects. However, the complexes formed by alginate and Ca(2+) (>5 mM) might play a bridging role and thus enhanced MnO2 colloidal aggregation instead. These results may be important for assessing the fate and transport of MnO2 colloids and associated contaminants.

Simultaneous titration of ternary alkaline–earth mixtures employing a potentiometric electronic tongue

A fast novel complexometric titration procedure is proposed, in which equivalence concentrations were determined using a potentiometric electronic tongue. The titration consists in a reduced number of fixed additions of titrant and the recording of the potentials of an array of ion-selective electrodes with cross-selectivity response. The generated data (number of sensors × number of additions) were used as input data to an artificial neural network response model previously trained with standards. The application of this procedure is demonstrated with automated EDTA titrations of Ca 2+, Mg 2+ and Sr 2+ mixtures, up to 3.3 mM total ion concentration. In the studied case, good results predicting the three concentrations were obtained using five 1 mL fixed volume additions plus the readings of eight sensors. The unique additional step required was the pH buffering of the sample to pH 9.5. Good comparisons were observed between obtained and expected concentrations for the three cations with the external validation samples ( n = 17, with RMSE values of 0.18, 0.28 and 0.32 mM for Ca 2+, Mg 2+ and Sr 2+, respectively). The proposed procedure was applied to mineral waters and compared with reference methods.

Noradrenaline-induced cation currents in isolated rat paratracheal ganglion neurons

The actions of noradrenaline (NA) on the neurons acutely isolated from paratracheal ganglia of rats and the ionic mechanisms involved were studied with nystatin-perforated patch recording configuration. Under current-clamp conditions, application of 10 μM NA produced membrane depolarization followed by repetitive action potentials. NA evoked an inward cationic current under voltage-clamp conditions at a holding potential of −60 mV. Transient tail inward (‘hump’) current was also induced by washout of NA. The NA-induced current was reduced by extracellular Ca 2+ and Mg 2+, with half-maximal concentrations of 0.7 and 2.6 mM for Ca 2+ and Mg 2+, respectively. Phenylephrine, an α 1-adrenoceptor agonist, mimicked the NA-induced current, but the ‘hump’ current did not occur upon washout of phenylephrine. The NA-induced current was inhibited by prazosin and WB-4101, α 1-adrenoceptor antagonists. In contrast, in the presence of yohimbine, an α 2-adrenoceptor antagonist, the NA-induced current was potentiated and the washout of NA failed to evoke the ‘hump’ current. The pretreatment of paratracheal neurons with pertussis toxin also potentiated the NA-induced current. The NA-induced inward current was inhibited by pretreatment with U73122, a phospholipase C inhibitor, and xestospongin-C, a membrane-permeable IP 3 receptor antagonist. On the other hand, thapsigargin, BAPTA-AM and calmidazolium had no effect on the NA-induced current, suggesting that release of Ca 2+ from intracellular Ca 2+ stores via IP 3 receptors is not involved in the NA action. The cationic channels activated by NA play an important physiological role in neuronal membrane depolarization in rat paratracheal ganglia.

Extracellular Ca(2+)-sensing receptor is a promiscuous divalent cation sensor that responds to lead.

The extracellular Ca(2+)-sensing receptor (CaR) responds to polycations, including Ca(2+) and neomycin. This receptor is a physiological regulator of systemic Ca(2+) metabolism and may also mediate the toxic effects of hypercalcemia. A number of divalent cations, including Pb(2+), Co(2+), Cd(2+), and Fe(2+), are toxic to the kidney, brain, and other tissues where the CaR is expressed. To determine which divalent cations can activate the CaR, we expressed the human CaR in HEK-293 cells and measured activation of phospholipase A(2) (PLA(2)) and the mitogen-activated protein kinase p42ERK in response to potential agonists for the receptor. HEK-293 cells expressing the nonfunctional mutant CaR R796W served as controls. Extracellular Ca(2+), Ba(2+), Cd(2+), Co(2+), Fe(2+), Gd(3+), Ni(2+), Pb(2+), and neomycin activated the CaR, but Hg(2+) and Fe(3+) did not. We analyzed the kinetics of activation of p42ERK and PLA(2) by the CaR in response to Ca(2+), Co(2+), and Pb(2+). The EC(50) values ranged from approximately 0.1 mM for Pb(2+) to approximately 4.0 mM for Ca(2+). The Hill coefficients were >3, indicating multiple cooperative ligand binding sites or subunits. Submaximal concentrations of Ca(2+) and Pb(2+) were additive for activation of the CaR. The EC(50) for Ca(2+) or Pb(2+) was reduced four- to fivefold by the presence of the other ion. These divalent cations also activated PLA(2) via the CaR in Madin-Darby canine kidney cells that stably express the CaR. We conclude that many divalent cations activate the CaR and that their effects are additive. The facts that the CaR is a promiscuous polycation sensor and that the effects of these ions are additive to activate it suggest that the CaR may contribute to the toxicity of some heavy metals such as Pb(2+), Cd(2+), Co(2+), and Fe(2+) for the kidney and other tissues where it is expressed.

A comparison between potencies of external calcium, strontium and barium to support GABAergic synaptic transmission in rat cultured hippocampal neurons

Relative potencies of external Ca 2+, Sr 2+ and Ba 2+ to trigger GABAergic synaptic transmission were evaluated by applying the patch-clamp technique to both presynaptic and postsynaptic hippocampal neurons prepared from neonatal rats. Action potentials were evoked by application of voltage pulses to presynaptic neurons, and GABAergic synaptic currents were recorded in voltage-clamped postsynaptic neurons. No stimuli were delivered during replacement with test solutions and only five pulses were applied to the presynaptic neuron in each test solution. During the five-pulse application, the amplitude of synaptic currents was constant in Ca 2+-containing solutions, but decreased successively in Ba 2+- and Sr 2+-containing solutions without Ca 2+. Thus, the amplitude of synaptic currents induced by the first pulse in each ionic condition was used to evaluate the potency of divalent cations. The lowest external concentration required to trigger the transmission was 0.3 mM for Ca 2+, 1 mM for Sr 2+ and 2 mM for Ba 2+, and the concentration required to achieve the same effect as with 2 mM Ca 2+ was 6 mM for Sr 2+ and 10 mM for Ba 2+. These results strongly suggest that Ba 2+ as well as Sr 2+ can be substituted for Ca 2+ in GABAergic synaptic transmission and the order of potency is Ca 2+ > Sr 2+ > Ba 2+.

Interference of Mg 2+ and Ca 2+ on protein determination with Lowry's method

The effect of Mg 2+ (0.84–6.74 mM) and Ca 2+ (0.18–1.45 mM) on the Lowry method was studied. Mg 2+ and Ca 2+ affected the absorbance of both the protein-free blank and protein samples. The tolerable limit was <0.84 mM for Mg 2+ and 0.55 mM for Ca 2+. The interference by Mg 2+ was more significant than Ca 2+ at the same concentration. A hypothesis was proposed in respect of the mechanism of interference by Mg 2+: the Mg(OH) 2 precipitate binds with protein and some constituent of Lowry reagent B and thus reduces their sensitivity to Folin reagent.

Salt-mediated effects in nonionic lipid bilayers constituted of digalactosyldiacylglycerol studied by FTIR spectroscopy and molecular modellization

Digalactosyldiacylglycerol (DGDG; Galppα1-6Galpβ1-3DAG) is one of the two nonionic species of the thylakoid membrane of higher plant chloroplasts where it constitutes about 29% of the total lipid content. This high concentration led to the conjecture that DGDG intervenes in the molecular organization and function of the thylakoid membrane. In this respect, we show that the DGDG membranes undergo aggregation but not fusion, at salt concentrations in the incubation media above a threshold characteristic of every ionic species, i.e., about 1.0 and 4.5-4.7 mM for Ca 2+ and Mg 2+ , respectively

Amino Acid Content of Fino and Oloroso Sherry Wines

The amino acid content was determined in two types of sherry wines, fino and oloroso. These compounds were also determined in young unfortified wines, used as starting material and at intervals during the various aging procedures under study. The amino acid proline, initially present at a concentration of 4 to 6 mM and accounting for ca 50% of the total amino acids, fell continuously throughout the aging procedure and also during the preparation of the fino wines. It fell to a value of ca 1 mM at the end, constituting just 20% of the total amino acids. This is probably the result of its preferential consumption by the yeast film present during the aging of the wine in oak wood butts. In oloroso wines, there is a slight increase in proline at the end of their physico-chemical aging in oak wood butts.

A Mg 2+-independent high-affinity Ca 2+-stimulated adenosine triphosphatase in the plasma membrane of rat stomach smooth muscle. Subcellular distribution and inhibition by Mg 2+

Plasma membrane enriched fraction isolated from the fundus smooth muscle of rat stomach displayed Ca 2+-stimulated ATPase activity in the absence of Mg 2+. The Ca 2+ dependence of such an ATPase activity can be resolved into two hyperbolic components with a high affinity ( K m = 0.4 μM ) and a low affinity ( K m = 0.6 mM ) for Ca 2+. Distribution of these high-affinity and low-affinity Ca 2+-ATPase activities parallels those of several plasma membrane marker enzyme activities but not those of endoplasmic reticulum and mitochondrial membrane marker enzyme activities. Mg 2+ also stimulates the ATPase in the absence of Ca 2+. Unlike the Mg 2+-ATPase and low-affinity Ca 2+-ATPase, the plasmalemmal high-affinity Ca 2+-ATPase is not sensitive to the inhibitory effect of sodium azide or Triton X-100 treatment. The high-affinity Ca 2+-ATPase is noncompetitively inhibited by Mg 2+ with respect to Ca 2+ stimulation. Such an inhibitory effect of Mg 2+ is potentiated by Triton X-100 treatment of the membrane fraction. Calmodulin has little effect on the high-affinity Ca 2+-ATPase activity of the plasma membrane enriched fraction with or without EDTA pretreatment. Findings of this novel, Mg 2+-independent, high-affinity Ca 2+-ATPase activity in the rat stomach smooth muscle plasma membrane are discussed with those of Mg 2+-dependent, high-affinity Ca 2+-ATPase activities previously reported in other smooth muscle plasma membrane preparations in relation to the plasma membrane Ca 2+-pump.

Chloral hydrate inhibition in vitro of ATPase in membrane of rat erythrocytes and in microsomes of dog kidney external medulla

The study of the general anesthetic chloral hydrate and its effects on rat erythrocyte membranes and dog kidney microsomes showed that ATPases were reversibly inhibited in every case. The inhibition was cooperative in the cases of (Mg 2− + Na − + K +)-ATPase, Mg 2−-ATPase and (Na + + K −)-ATPase of rat erythrocyte membrane, while Ca 2−-ATPase and (Mg 2− + Ca 2−)-ATPase were non-cooperative. The chloral hydrate concentrations necessary to diminish the activity of the enzyme to half of the V max (I 50) were 6 mM for Ca 2+-ATPase from erythrocyte membranes and 82 mM for Mg 2−-ATPase from intact external kidney medulla microsomes. When Ca 2−-ATPase was studied in the absence of Mg 2+ in these microsomes, the affinity for Ca 2− was very low, but the enzyme was sensitive to chloral hydrate.

Evidence on the role(s) of atp in the mechanism of nitrogenase, from proton nmr relaxation studies on metal and nucleotide binding to the molybdenum-iron protein

Interactions between the molybdenum-iron protein (Kp1) of nitrogenase (reduced ferredoxin:dinitrogen oxidoreductase (ATP-hydrolysing), EC 1.18.2.1) from Klebsiella pneumoniae and the divalent ions, Mn 2+, Mg 2+, Ca 2+ and Ba 2+, have been studied by monitoring the water proton NMR relaxation enhancement caused by the paramagnetism of Mn 2+. We observe several binding sites for Mn 2+, equivalent within experimental error ( K d = 209∓23 μM), increasing in number from 1.0 to 2.9 per molecule in direct proportion to the specific activity of the protein. Metal binding sites on the MoFe protein are therefore essential to the enzymic function of nitrogenase. A maximum of four such sites is inferred for the fully active protein molecule. All manganese sites can alternatively bind the diamagnetic ions studied, the binding being one order-of-magnitude weaker ( K d = 2.2∓0.3 mM for Mg 2+; 1.6∓0.2 mM for Ca 2+; 3.4∓0.3 mM for Ba 2+). ATP and ADP form ternary complexes via Mn 2+ with Kpl. The above data and other evidence on MgATP binding are discussed in terms of the site of hydrolysis of ATP during turnover and its possible bridging role between the two protein components of the enzyme.

Comparison of kinetic characteristics of Na + -Ca 2+ exchange in sarcolemma vesicles and cultured cells from chick heart

The kinetic characteristics of Na + -Ca 2+ exchange in isolated sarcolemma vesicles from new-borne chick heart, which contain about 70% of right-side-out vesicles, were compared with those of cultured embryonic chick heart cells. Na + -Ca 2+ exchange was monitored as Na i-dependent Ca 2+ uptake. Increase in the internal concentration of Na + ([Na +] i) in these two preparations caused increase in both the initial rate and the saturation-level of Ca 2+ uptake. Plots of the rate of Ca 2+ uptake against [Na +] i showed similar saturation-kinetics in these two preparations. The apparent Michaelis constant ( K m ) (0.35 mM) for Ca 2+ uptake by the intact cells was much higher than that (0.031 mM) for Ca 2+ uptake by the vesicles. The degree of inhibition by Mg 2+ was also higher in the cells than in the vesicles. Some possible reasons (age of the chicks used, membrane potential, etc.), for these differences were examined and are discussed.

Spectral analysis of fluorescence of 8-anilino-1- naphthalenesulfonate in chemoreception with a white plasmodium of Physarum polycephalum Evidence for conformational change in chemoreceptive membrane

A plasmodial mutant (strain Lu 647 × Lu 861) of Physarum polycephalum contains much less yellow pigment compared with the wild type. Thus, extrinsic fluorescence measurements should be possible with the use of this white plasmodium. We adopted 8-anilinonaphthalenesulfonate (ANS) as a fluorescent anion, and measured fluorescence spectra and polarization in conjunction with the membrane potential when the cell was stimulated with various salts. Results are: 1. (1) The membrane potential, Δϕ, did not change until the concentration of stimulus chemicals exceeded respective thresholds, C th . Above C th , Δϕ depolarized linearly with log C. The Schulze-Hardy rule was applicable to C th ; i.e. log C th = − log z + log K H where z is the valency of the cations. The Hamaker constant, K H , displayed two distinct values depending on the cation species: K H = 3 mM for Ca, La and Th (Group I) and K H = 0.2 mM for Na, K, NH 4, Mg, Ba and Al (Group II). The value of K H in the wild type was 3 mM for all polyvalent cations examined. 2. (2) When excited at 360 nm, ANS gave two emission maxima of 500–510 nm and 460 nm through interaction with the plasmodial membrane. Application of an Mg or Na salt of ANS below the respective C th gave a single peak at 500 nm, while that above C th caused an increase in fluorescence intensity at 460 nm. 3. (3) Fluorescence polarization, p, at 460 nm decreased appreciably when an Mg or Na salt of ANS above the respective C th was applied to the plasmodium. Addition of CACl 2, LaCl 3 or Th(NO 3) 4 caused an increase in the p value, while that of KCl, NaCl, MgCl 2 or AlCl 3 did not. Results described above indicate that the plasmodial membrane undergoes a conformational change upon salt reception. Based on the physicochemical properties of ANS, we may conclude that chemoreceptive membrane of the plasmodium becomes more hydrophobic above C th .

Divalent cation-induced interaction of phospholipid vesicle and monolayer membranes

The effects of phospholipid vesicles and divalent cations in the subphase solution on the surface tension of phospholipid monolayer membranes were studied in order to elucidate the nature of the divalent cation-induced vesicle-membrane interaction. The monolayers were formed at the air/water interface. Various concentrations of unilamellar phospholipid (phosphatidylserine, phosphatidylcholine and their mixtures) vesicles and divalent cations (Mg 2+, Ca 2+, Mn 2+, etc.) were introduced into the subphase solution of the monolayers. The changes of surface tension of monolayers were measured by the Wilhelmy plate (Teflon) method with respect to divalent ion concentrations and time. When a monolayer of phosphatidylserine and vesicles of phosphatidylserine/phosphatidylcholine (1 : 1) were used, there were critical concentrations of divalent cations to produce a large reduction in surface tension of the monolayer. These concentrations were 16 mM for Mg 2+, 7 mM for Sr 2+, 6 mM for Ca 2+, 3.5 mM for Ba 2+ and 1.8 mM for Mn 2+. On the other hand, for a phosphatidylcholine monolayer and phosphatidylcholine vesicles, there was no change in surface tension of the monolayer up to 25 mM of any divalent ion used. When a phosphatidylserine monolayer and phosphatidylcholine vesicles were used, the order of divalent ions to effect the large reduction of surface tension was Mn 2+ > Ca 2+ > Mg 2+ and their critical concentrations were in between the former two cases. The threshold concentrations also depended upon vesicle concentrations as well as the area/molecule of monolayers. For phosphatidylserine monolayers and phosphatidylserine/phosphatidylcholine (1 : 1) vesicles, above the critical concentrations of Mn 2+ and Ca 2+, the surface tension decreased to a value close to the equilibrium pressure of the monolayers within 0.5 h. This decrease in surface tension of the monolayers is interpreted partly as the consequence of fusion of the vesicles with the monolayer membranes. The