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PubMed1982

Local anesthetics and divalent cations have the same effect on the headgroups of phosphatidylcholine and phosphatidylethanolamine.

The effects of the local anesthetic dibucaine on the membrane headgroup conformations of phosphatidylcholine and phosphatidylethanolamine were determined using 2H- and 31P-NMR. The size of the deuterium quadrupole splittings of the two methylene segments of the choline and ethanolamine groups changed dramatically and the 31-phosphorus chemical shift anisotropy of the phosphatidylcholine headgroup decreased by about 7 ppm in the presence of local anesthetic. The quadrupole splittings of the 3-glycerol and choline methyl segments were relatively insensitive to the addition of dibucaine. The headgroup data for dibucaine addition paralleled similar data for the addition of various cations. These NMR results agree with the previous observation that these drugs displace calcium from phospholipids. The effects of this local anesthetic on these headgroups were distinctly different from the changes induced by cholesterol, heat and the general anesthetic chloroform.

Cations, Divalent↗
PubMed1983

Anion influence on the binding of divalent cations to phosphatidylcholine.

We have used the osmotic pressure technique of Rand, Parsegian and co-workers (Nature 259 (1976) 601-603) to investigate the effect of anion species on the binding of M2+ to dipalmitoylphosphatidylcholine bilayers. Calcium and magnesium salts show a complex behavior which is consistent with both anion binding and screening. We observe virtually no change, within the accuracy of our experiment, in the decay of repulsive pressure with inter-bilayer separation for the acetate and nitrate salts of magnesium and calcium; however, the chloride salt does show a different pressure decay. At any given bilayer separation, 35 A less than dw less than 75 A, with calcium and magnesium salts present, the anions produce a decrease in the repulsive pressure in the order acetate- greater than Cl- greater than NO-3.

Anions↗
PubMed1986

Electrophysiology of phagocytic membranes. Role of divalent cations in membrane hyperpolarizations of macrophage polykaryons.

The electrophysiological properties of the membrane of mouse peritoneal macrophage polykaryons are studied. Slow hyperpolarizations can be elicited by iontophoretic injections of either Ca2+ or Sr2+ into the cytoplasm. The effect of both cations is identical, since: it is invariably triggered by the cation injection, the amplitude is dependent on the K+ gradient, quinine blocks reversibly the response to both cation injections. Mg2+, Ba2+ and Mn2+ did not elicit responses when injected into the cytoplasm. Ca2+ induced slow hyperpolarizations were reversibly blocked by the addition of Ba2+ to the external saline, but were not affected by the presence of external tetraethylammonium chloride. Cells maintained in saline containing high concentrations of Ca2+, Sr2+ or Mn2+ exhibited sustained hyperpolarizations. Quinine blocked the hyperpolarization induced by high Ca2+ or Sr2+, but was ineffective for the case of Mn2+. Cells hyperpolarized by external Mn2+ frequently exhibited nonlinear, voltage-current characteristics. Similar patterns could also be observed in a small fraction (less than 10%) of the cells in control conditions. Current-induced shifts between two stable membrane potentials were seen either in high Ca2+ or normal medium. The great variability of the responses described for this phagocytic membrane is discussed. The evidence supports the assumption that Ca2+ and Sr2+ can induce transient or persistent hyperpolarized states by activating a potassium permeability. External Mn2+ may act in part by reducing impalement-related current leakage from the phagocytic membrane.

Animals↗
PubMed1988

Precipitation of solubilized Na+/K+-ATPase by divalent cations.

A method for preparation of membranous fragments of pure and highly active shark rectal gland Na+/K+-ATPase by Mn2+ precipitation of C12E8-solubilized enzyme is described. The method is rapid and inexpensive, and yields enzyme with a specific Na+/K+-ATPase activity of up to 1800 mumol/mg per h at 37 degrees C. The influence of the detergent/protein and lipid/protein ratios on the yield of membrane bound enzyme is described.

Animals↗
PubMed1989

Protection of cells against membrane damage by haemolytic agents: divalent cations and protons act at the extracellular side of the plasma membrane.

The protective effect of Ca2+, Zn2+ and H+ against membrane damage induced by different haemolytic agents has been studied by measuring monovalent cation leakage and haemolysis of erythrocytes, and phosphoryl[3H]choline and adenine nucleotide leakage from Lettre cells prelabelled with [3H]choline. The protective effect of Ca2+ and Zn2+ on erythrocytes damaged by Staphylococcus aureus alpha-toxin, Sendai virus or melittin is unaffected by the addition of A23187, even though this ionophore greatly increases the uptake of 45Ca2+ or 65Zn2+. The same result has been found for the protective effect of Zn2+ on Lettre cells damaged by S. aureus alpha-toxin, Sendai virus, melittin or Triton X-100. Leakage of phosphoryl[3H]choline from prelabelled Lettre cells is inhibited if extracellular pH is lowered; lowering the intracellular pH without affecting the extracellular pH, affords little protection. It is concluded that Ca2+, Zn2+ and H+ protect cells against membrane damage induced by haemolytic agents by an action at the extracellular side of the plasma membrane.

Animals↗
PubMed1990

A putative K(+)-selective channel in the plasma membrane of yeast that is blocked by micromolar concentrations of external divalent cations and is insensitive to tetraethylammonium.

At pH 7, addition of glucose to an anaerobic suspension of non-metabolizing yeast cells causes a transient net efflux of K+ from the cells and a concomitant transient hyperpolarization of the plasma membrane (Van de Mortel, J.B.J., et al. (1988) Biochem. Biophys. Acta 936, 421-428). Both phenomena are effectively suppressed in the presence of low concentrations of polyvalent cations. The concentrations of Mn2+, Ca2+, Ba2+, Mg2+, Sr2+ and La3+ required for half-maximal suppression of the transient hyperpolarization are 10, 17, 20, 38, 47 and 5 microM, respectively. Subsequent addition of EDTA 90 s after that of Ca2+ immediately restores both K+ efflux and cellular uptake of the fluorescent membrane potential probe 2-(dimethylaminostyryl)-1-ethylpyridinium (DMP). This suggests that an interaction of polyvalent cations with an external binding site blocks the putative K(+)-selective channel. Opening of this channel is not blocked by 20 mM tetraethylammonium nor by 100 microM 3,4-diaminopyridine. It is argued that this glucose-induced K(+)-conductive pathway is not identical to the voltage-gated K+ channels identified until now in patch-clamp studies of the yeast plasma membrane.

4-Aminopyridine↗
PubMed1990

Maintenance of lipid asymmetry in red blood cells and ghosts: effect of divalent cations and serum albumin on the transbilayer distribution of phosphatidylserine.

The maintenance of lipid asymmetry in the plasma membrane of human red blood cells (RBC) was investigated by assessing the equilibrium distribution of exogenously inserted NBD-labeled phosphatidylserine (PS) and endogenous PS in RBC and hypotonically lysed ghosts. PS distribution was determined by the ability to 'back-exchange' NBD-lipids into acceptor membranes and bovine serum albumin, and by prothrombinase complex assay for endogenous PS. To maintain the normal asymmetric distribution of PS in RBC, ghosts required Mg2+ in the lysis buffer. The inclusion of Ca2+, even in the presence of Mg2+ resulted in complete randomization of endogenous and exogenously inserted PS. These results indicate that NBD-labeled PS analogs faithfully monitor the distribution of endogenous PS during ghost preparation. In contrast, treatment of RBC with bovine serum albumin had no effect on the distribution of endogenous PS, although it resulted in a time-dependent movement of NBD-labeled PS from the inner to the outer leaflet (flop). This phenomenon was dependent on continuous incubation in the presence of albumin and could not be duplicated when pure acceptor membranes were used.

4-Chloro-7-nitrobenzofurazan↗
PubMed1991

Effects of divalent cations and pH on amiloride-sensitive Na+ fluxes into luminal membrane vesicles from pars recta of rabbit proximal tubule.

The effect of Ca2+, Cd2+, Ba2+, Mg2+ and pH on the renal epithelial Na(+)-channel was investigated by measuring the amiloride-sensitive 22Na+ fluxes into luminal membrane vesicles from pars recta of rabbit proximal tubule. It was found that intravesicular Ca2+ as well as extravesicular Ca2+ substantially lowered the channel-mediated flux. Amiloride sensitive Na+ uptake was nearly completely blocked by 10 microM Ca2+ at pH 7.4. The inhibitory effect of Ca2+ was dependent on pH. Thus, 10 microM Ca2+ produced 90% inhibition of 22Na+ uptake at pH 7.4, and only 40% inhibition at pH 7.0. The tracer fluxes measured in the absence of Ca2+ were pH independent over the range from 7.0 to 7.4. All the cations Ca2+, Cd2+, Ba2+ except Mg2+ inhibited the 22Na+ influx drastically when added extravesicularly in millimolar concentrations. The cations Cd2+, Ba2+ and Mg2+ in the same concentrations intravesicularly inhibited the 22Na+ influx only slightly. A millimolar concentration of Ca2+ intravesicularly blocked the amiloride-sensitive 22Na+ flux completely. The data indicate that Ca2+ inhibits Na+ influx specifically by binding to sites composed of one or several deprotonated groups on the channel proteins.

Amiloride↗
PubMed1993

Human immunodeficiency virus type 1 (HIV-1) fusion with model membranes: kinetic analysis and the role of lipid composition, pH and divalent cations.

The kinetics and extent of HIV-1 fusion with model membranes was studied. HIV-1 was labeled with octadecyl rhodamine B chloride, and fusion was monitored continuously as the dilution of the probe into target membranes. The results were analyzed by a mass action model which yielded good simulations and predictions for the kinetics and final extents of fluorescence increase. The model determined the percent of virions capable of fusing and rate constants of fusion, aggregation and dissociation. Ultrastructural analysis of the virus and reaction products by electron microscopy also provided evidence of HIV-1 fusion with membranes lacking CD4. HIV-1 fusion activity depends on the target membrane lipid composition according to the sequence: cardiolipin (CL) > > phosphatidylinositol > CL/dioleoylphosphatidylcholine (DOPC) (3:7), phosphatidic acid > phosphatidylserine (PS), PS/cholesterol (2:1) > PS/PC (1:1), PS/phosphatidylethanolamine (1:1) > DOPC, erythrocyte ghosts. Reduction of pH from 7.5 generally enhances the rate and extent of HIV-1 fusion. Physiologically relevant concentrations of calcium stimulate HIV-1 fusion with several liposome compositions and with erythrocyte ghost membranes. The fusion products of HIV-1 with liposomes consist of a single virus and several liposomes. The mass action analysis revealed that, compared to intact virions, the fusion products show a striking reduction in the fusion rate constant. Like influenza and Sendai viruses, HIV-1 fusion with membranes containing its own envelope glycoprotein(s) is strongly inhibited. Unlike these viruses, HIV-1 fusion is promoted by physiological levels of calcium. HIV-1 fusion with liposomes is qualitatively similar to simian immunodeficiency virus fusion.

Cardiolipins↗
PubMed1980

Studies on in activation and reactivation of homogeneous rabbit liver phosphoprotein phosphatases by inorganic pyorphosphate and divalent cations.

Preincubation of two homogeneous rabbit liver phosphoprotein phosphatases (phosphophoprotein phosphohydrolases, EC 3.1.3.16) (Khandelwal, R.L., Vandenheede, J.R. and Krebs, E.G. (1976) J. Biol. Chem. 251, 4850-4858) with ATP, ADP and PPi caused a time- and concentration-dependent inactivation of the enzyme activity. A 50% inactivation of phosphoprotein phosphatase I required relatively low concentration of inactivating metabolite and less preincubation time as compared to the inactivation of phosphoprotein phosphatase II. AMP, adenosine, adenine, Pi, EDTA, EGTA, 1,10-phenanthroline and diethyl dithiocarbamate were without effect on both enzymes. Pretreatment of both enzymes by metal-chelating agents followed by PPi did not augment the effect observed with PPi alone. Both inactivated enzymes could be reactivated by cobalt or manganese in the presence of dithiothreitol. Although the extent of reactivation by these two metal ions was almost similar, cobalt required a ten times lower concentration than manganese for this process. No difference in inactivation or reactivation of both enzymes was observed with different substrates, phosphorylase a, histone or casein, employed in the assay. Pi and PPi added during the assay inhibited activities of both phosphatases with phosphorylase a and casein substrates. With histone as substrate, PPi slightly inhibited enzyme activities at lower concentrations (0.01-0.25 mM) but activated at higher concentrations. Pi activated both enzymes with this substrate; maximal activation being observed at a concentration of 5 mM.

Adenosine Diphosphate↗
PubMed1986

An ESR study of the effect of an electrostatic field on binding of divalent cations to the surface of serum low-density lipoproteins.

The ESR technique has been used to study binding of Mn(II) ions to low-density lipoprotein (LDL) in solutions of various electrolyte ionic strengths. A model of the binding has been proposed which describes all the observations in electrolytes of ten different concentrations in terms of two types of binding sites and two corresponding sets of intrinsic binding parameters (n1 = 8, Kd1 = 1.31 X 10(-3) mol X l-1 and n2 = 170, Kd2 = 5.71 X 10(-2) mol X l-1). These parameters, together with the values of the potential (phi 0) responsible for binding of the ions to specific charged sites on the surface, reproduce the observed binding curves well in all the systems studied. The phi 0 values are obtained as an appropriate solution of the Poisson-Boltzmann equation.

Binding Sites↗