Calcium binding by the erythrocyte membrane

Hyperpolarization/depolarization on human spermatozoa

The accumulation of the lipophilic cation radiolabeled triphenylmethylphosphonium (TPMP+) was utilized to determine the resting membrane potential across the plasma membrane (psi) of human sperm. Washed sperm were suspended and incubated in low-K+ and high-K+ medium and allowed to take up the cation to a steady state (20 min at 37 degrees C). By using this differential, the value obtained was inserted in the Nernst equation and the value yielded a psi of -69 +/- 2 mV. When the Na+ or K+ concentration is high in the medium, the accumulation of TPMP+ in the membrane sperm cells was increased or decreased, respectively, inducing hyperpolarization and depolarization of the membrane 20% and 85%, respectively. The presence of divalent cations Zn++ and Mg++ in the incubation medium both induced a hyperpolarization of 10% and 8.6%, respectively. The addition of specific reagents such as p-chloromercuribenzenosulfonate and ethylenediaminetetraacetic acid sodium salt both decreased the psi 35% and 58%, respectively. The agents acting on the sperm cell membrane, such as dithiothreitol and progesterone, both induced hyperpolarization and depolarization of the membrane 16% and 40%, respectively. The presence of propranolol and L-alpha-lysophosphatidylcholine, which affect the ionic gradients present across the plasma membrane, both induced a depolarization from 43% and 92%, respectively. Finally the psi was glucose-dependent. The result of these studies was that, by the use of agents causing hyperpolarization or depolarization, we obtained changes in the psi of -83.4 +/- 2.2 mV, until -6 +/- 0.6 mV changes of -76.8 +/- 2 mV translated across the sperm cell membrane.

Interaction of p-aminobenzoic acid with erythrocyte membrane: photoaffinity labeling of the binding sites

p-Aminobenzoic acid (PABA) was found to prevent eichinocytosis of red cells in vitro. Equilibrium binding studies with right-side-out membrane vesicles revealed a similar number of binding sites and Kd values for both normal and sickle cell membranes. A [14C]Azide analog of PABA was synthesized as a photoaffinity label to probe its sites of interaction on the erythrocyte membranes. Competitive binding studies of PABA with its azide indicated that both the compounds share common binding sites on the membrane surface. The azide was found to covalently incorporate into the membrane components upon irradiation; 52-35% of the label was associated with the proteins and the remaining with the lipids. Electrophoretic analysis of photolabeled membranes revealed that the azide interacts mainly with Band 3 protein in the case of intact erythrocytes and right-side-out sealed vesicles; however, if unsealed ghosts are used, other membrane proteins besides Band 3 are photolabeled. PABA was found to inhibit both high and low affinity calcium-binding sites situated on either surface of the membrane apparently in a non-competitive manner. However, calcium binding stimulated by magnesium and ATP was only slightly affected. Calcium transport into inside-out vesicles was inhibited by PABA, but it did not affect the calcium ATPase activity.

Lithium prophylaxis of recurrent affective disorders

The mode of action of lithium is reviewed in the light of advances in the understanding of calcium channelling and calmodulin-activated Ca ATPase. The relevance to changes in receptor sensitivity is discussed.

Effects of the skin mitogens tumor-promotor 12-O-tetradecanoylphorbol 13-acetate and divalent-cation-ionophore A23187 on ion fluxes and membrane potential in a murine epidermal cell line (HEL30) and in 3T3 fibroblasts

The transmembrane potential of HEL30 keratinocytes and 3T3 fibroblasts has been determined by measuring the distribution of labelled triphenylmethylphosphonium bromide. The tumor-promotor 12-O-tetradecanoylphorbol 13-acetate (1-5 microM) induces hyperpolarization in 3T3 cells but does not exert any effect on the membrane potential of keratinocytes, whereas the divalent cation ionophore A23187 (0.5 - 1 microM) hyperpolarizes keratinocytes and probably also 3T3 cells. Studies on Na+ and Rb+ fluxes, as well as with different inhibitors, indicate that the hyperpolarizing effect is the consequence of an increased Na+ influx which in turn stimulates the Na+/K+-dependent ATPase. No causal relationship seems to exist between the change of the membrane potential and arachidonic acid release (and subsequent prostaglandin synthesis) which is induced by both drugs in both cell lines. Since the induction of the arachidonic cascade (by both agents) as well as the stimulation of Na+ influx (by A23187) are found to be critically dependent on extracellular Ca2+ and are inhibited by 'Ca2+-blockers', it is concluded that both reactions are triggered by the same event (Ca2+ translocation) but proceed independently of each other. The release of arachidonic acid is already stimulated under conditions where a measurable influx of Ca2+ is not yet observed. This indicates a local mobilization of Ca2+, perhaps across the plasma membrane. It is concluded that monovalent cation fluxes and changes of the membrane potential are not critically involved in the stimulation of the arachidonic acid cascade and cellular proliferation by agents which induce epidermal hyperplasia in vivo.

A high-affinity, calmodulin-sensitive (Ca2+ + Mg2+)-ATPase and associated calcium-transport pump in the Ehrlich ascites tumor cell plasma membrane

A unique cytoplast preparation from Ehrlich ascites tumor cells (G. V. Henius, P. C. Laris, and J. D. Woodburn (1979) Exp. Cell. Res. 121, 337-345), highly enriched in plasma membranes, was employed to characterize the high-affinity plasma membrane calcium-extrusion pump and its associated adenosine triphosphatase (ATPase). An ATP-dependent calcium-transport system which had a high affinity for free calcium (K0.5 = 0.040 +/- 0.005 microM) was identified. Two different calcium-stimulated ATPase activities were detected. One had a low (K0.5 = 136 +/- 10 microM) and the other a high (K0.5 = 0.103 +/- 0.077 microM) affinity for free calcium. The high-affinity enzyme appeared to represent the ubiquitous high-affinity plasma membrane (Ca2+ + Mg2+)-ATPase (calcium-stimulated, magnesium-dependent ATPase) seen in normal cells. Both calcium transport and the (Ca2+ + Mg2+)-ATPase were significantly stimulated by the calcium-dependent regulatory protein calmodulin, especially when endogenous activator was removed by treatment with the calcium chelator ethylene glycol bis(beta-aminoethyl ether) N,N'-tetraacetic acid. Other similarities between calcium transport and the (Ca2+ + Mg2+)-ATPase included an insensitivity to ouabain (0.5 mM), lack of activation by potassium (20 mM), and a requirement for magnesium. These similar properties suggested that the (Ca2+ + Mg2+)-ATPase represents the enzymatic basis of the high-affinity calcium pump. The calcium pump/enzyme system was inhibited by orthovanadate at comparatively high concentrations (calcium transport: K0.5 congruent to 100 microM; (Ca2+ + Mg2+)-ATPase: K0.5 greater than 100 microM). Upon Hill analysis, the tumor cell (Ca2+ + Mg2+)-ATPase failed to exhibit cooperative activation by calcium which is characteristic of the analogous enzyme in the plasma membrane of normal cells.

Ca2+ displacement by Polymyxin B from sarcolemma isolated by 'gas dissection' from cultured neonatal rat myocardial cells

Amphiphilic, cationic Polymyxin B is shown to displace Ca2+ from 'gas dissected' cardiac sarcolemma in a dose-dependent, saturable fashion. The Ca2+ displacement is only partially reversible, 57% and 63%, in the presence of 1 mM or 10 mM Ca2+, respectively. Total Ca2+ displaced by a non-specific cationic probe, lanthanum (La3+), at maximal displacing concentration (1 mM) was 0.172 +/- 0.02 nmol/microgram membrane protein. At 0.1 mM, Polymyxin B displaced 42% of the total La3+-displaceable Ca2+ or 0.072 +/- 0.01 nmol/microgram protein. 5 mM Polymyxin displaced Ca2+ in amounts equal to those displaced by 1 mM La3+. Pretreatment of the membranes with neuraminidase (removal of sialic acid) and protease leads to a decrease in La3+-displaceable Ca2+ but to an increase in the fraction displaced by 0.1 mM Polymyxin from 42% to 54%. Phospholipase D (cabbage) treatment significantly increased the La3+-displaceable Ca2+ to 0.227 +/- 0.02 nmol/microgram protein (P less than 0.05), a gain of 0.055 nmol. All of this phospholipid specific increment in bound Ca2+ was displaced by 0.1 mM Polymyxin B. The results suggest that Polymyxin B will be useful as a probe for phospholipid Ca2+-binding sites in natural membranes.

Ion transport in hypertension

A wide range of abnormalities of membrane sodium and potassium transport can be demonstrated in patients with essential hypertension, and in rats with genetic hypertension and with some forms of experimental hypertension. In the human red cell increased permeability to sodium and potassium, increased ouabain-sensitive sodium pumping, lithium-sodium counter-transport, and frusemide-sensitive co-transport have been described; by contrast, in the human leucocyte sodium pumping is reduced. In the spontaneously hypertensive rat and the rat with mineralocorticoid-induced hypertension, increased permeability to sodium and potassium, with increased ouabain-sensitive pumping, is shared by the red cell and the arterial smooth muscle. This abnormality is associated with decreased cell-membrane affinity for calcium and increased cell-membrane viscosity. It is proposed that in essential hypertension the decreased membrane affinity for calcium is a primary pathogenetic change giving rise to secondary changes in sodium and potassium transport.

Negatively charged sites and calcium binding in the isolated rat heart sarcolemma

Colloidal iron staining, calcium binding and enzyme activities were studied in the isolated rat heart sarcolemma. Colloidal iron staining of the sarcolemma revealed a high density of negatively charged sites associated with the cell surface. This membrane fraction was found to have calcium binding activity at both low (0.1 mM) and high (1.25 mM) concentrations of calcium. Pretreatment of the sarcolemma with either trypsin, phospholipase C or neuraminidase, was associated with a reduction in colloidal iron staining as well as decreased calcium-binding activity at high concentrations of calcium. Calcium binding at low concentrations was decreased by both trypsin and neuraminidase. Mg2+ ATPase, Ca2+ ATPase, and Na+-K+ ATPase activities were altered by neuraminidase and trypsin treatments, whereas phospholipase C treatment altered Na+-K+ ATPase only. It is concluded that both surface negative charge and calcium-binding sites associated with the isolated rat heart sarcolemma are contributed by a mosaic of biomolecules including proteins, phospholipids and glycoproteins, and alterations in the surface charge may influence the activities of membrane-bound enzymes.

Ca2+-activated ATPase and ATP-dependent calmodulin-stimulated Ca2+ transport in islet cell plasma membrane

Calcium is known to play an essential part in the regulation of insulin secretion in the pancreatic beta cell. Calcium influx/efflux studies indicate that glucose promotes an accumulation of calcium by the beta cell. However, interpretation of such data is particularly difficult due to the complex compartmentalization of calcium within the cell. Although indirect evidence using chlorotetracycline suggests that control of calcium homeostasis at the plasma membrane may be central to insulin secretion, the mechanism by which secretagogues influence the handling of calcium remains unknown. Despite its continuous diffusive entry, intracellular calcium is maintained in the submicromolar range by energy-dependent mechanisms. One such process which has been well characterized in erythrocytes is a plasma membrane calcium extrusion pump whose enzymatic basis is a high affinity (Ca+2 + Mg+2)ATPase. A similar mechanism regulated by insulin has recently been identified in adipocyte plasma membranes. We report here the presence of a high affinity (Ca+2 + Mg+2)ATPase and ATP-dependent calmodulin-stimulated calcium transport system in rat pancreatic islet cell plasma membranes.

Sickle red cell calcium metabolism: studies on Ca2+-Mg2+ATPase and Ca-binding properties of sickle red cell membranes

Sickle (Hb SS) red cells, preloaded with 45Ca by reversal of hemolysis, exhibit an incomplete 45Ca extrusion, retaining approximately four times more 45Ca than normal cells. Studies indicated that neither the reduction in Hb SS cell Ca2+-Mg2+ ATPase activity (84% of normal) nor the activation of Ca2+-Mg2+ ATPase by calmodulin was sufficiently different from normal cells to attribute a major role to the calcium pump in 45Ca retention. These results suggested that 45Ca retention may reflect an alteration in the calcium-binding properties of Hb SS cell membranes. Low-affinity calcium-binding (freely dissociable) was similar in normal and Hb SS cell membranes. However, the total calcium bound with high-affinity (tightly bound) was four-to-five times greater in Hb SS cell membranes than in normal membranes. These results are compatible with the hypothesis that Hb SS cell 45Ca retention reflects an exchange of a fraction of the total 45Ca with a tightly bound calcium pool, larger in Hb SS cell membranes than in normal membranes. A comparable degree of red cell 45Ca retention, which did not correlate with the reticulocyte population, was observed in other chronic anemic states. These findings suggest that the increased high-affinity calcium binding by the membrane may be a consequence of cellular changes induced by the anemic condition.

Inhibition of active strontium transport from erythrocyte ghosts by internal calcium: evidence for a specificity controlling site

The inhibition of strontium transport from erythrocyte ghosts by internal calcium was investigated. When active strontium transport was measured in the presence of increasing levels of internal calcium it was found that the inhibition of strontium transport started at an internal calcium level of 0.3 mM and was virtually complete when this concentration reached 1.0 mM. It was also noted that calcium transport was virtually constant between concentrations of 0.3 and 1.0 mM. This experiment indicated that calcium did not inhibit strontium transport by competing for the active site of the transport system. This inhibition was partially reversed by increasing the internal magnesium concentration from 1 to 4 mM. A higher level of magnesium at the time of lysis and during incubation enhanced strontium transport. However, the inhibition remained noncompetitive with respect to calcium. Manganese was also found to support calcium and strontium transport. However, it could not reverse the inhibition of strontium transport by internal calcium at any concentration tested. In fact, manganese restored the inhibition of strontium transport by calcium in ghosts that were prepared and incubated in solutions that had high magnesium levels.

Shape and stability changes in human erythrocyte membranes induced by metal cations

Asymmetric human erythrocyte ghost membranes behave as bilayer couple and exhibit a radius of curvature preference depending on the state of expansion or contraction of each side of the bilayer. The inside-out preference in the absence of added metal cations is gradually reduced as the K+ concentration is raised to 200 mM until a slight right-side-out preference may be exhibited Divalent cations (denoted 72+; Ca2+, Mg2+ and Mn2+) induce inside-out curvature at very low concentrations, right-side-out curvature at intermediate concentrations, and inside-out curvature again at high ones. This "triphasic" response is attributed to changes in the packing of acidic phospholipid (PL-) pairs in the A-face as a function of M2+ : PL- binding stoichiometry: 0 : 1 (PL- electrostatic repulsion and A-face expansion), 1 : 2 (PL2M crossbridging an contraction), and 1 : 1 (PLM+ repulsion and expansion). Generally increasing parent vesicle size is associated with higher cation concentrations. This is distinguished from the internal and external membrane blebbing preferred at different concentrations in accord with sidedness preference. Parent vesicle size was interpreted to be most closely associated with cation stabilisation (resistance to fragmentation) of the membrane, while sidedness and size (radius of curvature) of blebs were most closely correlated with packing of lipid molecules in the bilayer.

Chlorotetracycline induces calcium mediated shape changes in human erythrocytes. Is Ca asymmetrically distributed in the red cell membrane?

Calcium was localized in the red cell membrane by light microscopy using chlorotetracycline hydrochloride (CTC) as chelate probe. Treating human erythrocytes with CTC dissolved in saline free of divalent cations, leads to a 530 nm fluorescence emission in the cell border and to characteristic cell shape changes which were evaluated to assess intramembrane calcium distribution. CTC prevented and reverted erythrocyte crenation induced either by washing or superfusing the cells with saline. The ionophore A23187, EGTA and glucose depletion depressed the shape modifying effect of CTC. Thus, CTC appears to act on red cell shape by complex formation with membrane associated calcium. This is further confirmed by the failure of degraded CTC, devoid of metal binding capacity, to modify the crenated shape. The CTC effect can be reverted by superfusing the erythrocytes with CTC-free medium. Thus, calcium binds more tightly to the membrane than to CTC and is not displaced by the antibiotic. If the bilayer couple hypothesis [Sheetz, M.P., Singer, S.J., Proc. Natl. Acad. Sci. USA 71, 4457-4461 (1974)]applies, crenation is reverted by expansion of the inner membrane half relative to the outer membrane half. Expansion of the inner membrane half results from intercalation of CTC which binds to calcium. Thus, calcium in the red cell membrane preferentially occupies the inner leaflet of the bilayer.

Role of membrane-bound Ca in ghost permeability to Na and K

The permeability of red cell ghosts to K is determined by the amount of membrane-bound Mg which, in turn, depends on internal Mg. Contrasting with such effect, an increase in cellular Ca raises K permeability. To test whether this action is due to a competitive displacement of membrane Mg, the free Ca content of human red cell ghosts was altered by means of Ca-EGTA buffers. Net Na and K movements as well as Ca and Mg bindings were assessed after incubation in a Na-medium at 37 degrees C. Raising Ca from 3 X 10(-7) to 1 X 10(-2) M caused a large K efflux with very little Na gain. Under similar conditions, Ca binding was increased without affecting membrane-bound Mg. Both Ca binding and K loss were markedly diminished by either adding ATP to the hemolytic medium or increasing internal Mg at a fixed Ca concentration. A Scatchard analysis showed three Ca binding sites, two of them having high affinity. It is concluded that Ca action does not arise from a displacement of membrane-bound Mg but from binding to different sites in the membrane. Presumably, high affinity sites are involved in the control of K permeability.

[Kinetics of Ca 2+ or Mg 2+ activated ATPase from lymphocyte plasma membranes]

The kinetic study of the C2+ ATPase activity of lymphocyte plasma memebranes allowed some properties of this enzyme to be evidenced. The Ca2+-activated hydrolysis of ATP is independent of a non-specific alkaline phosphatase. The substrate of the ATPase activity is the chelate Ca2+- ATP. Mg2+ may substitute for Ca2+ both as chelating ion and as activating ion. Several results suggest that we have only one ATPase, activated either by Ca2+-, or by Mg2+ with less efficiency; both chelates hve the same Km; pH values for maximum activity and transition temperatures are identical; the effects of free ions are also the same, activation at low concentration and inhibition at high concentration.

Extraction and localization of a (Ca2+ and Mg2+)-stimulated ATPase in human erythrocyte spectrin

(1) A water soluble (Ca2+ plus Mg2+)-activated APTase has been extracted with 0.1 mM EDTA and 0.1 mM ATP from human erythrocyte membranes. (2) The specific activity of the extracted protein is increased 4- to 6-fold in comparison with untreated ghosts. (3) Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of [gamma-32P]ATP-labeled erythrocyte membranes shows that the (Ca2+ plus Mg2+)-activated ATPase is located in the "spectrin" region (Mr 220 000-240 000). The radioactivity of these high molecular peptide bands is decreased markedly after the extraction of the ATPase at low ionic strength.

The role of calcium in insulin action. III. Calcium distribution in fat cells; its kinetics and the effects of adrenaline, insulin and procaine-HCl

The effects of adrenaline, insulin and procaine-HCl on Ca distribution in intact fat cells and on Ca binding to fat cell ghost membranes have been investigated. 1. Fat cells incubated in 45Ca containing media till isotopic equilibrium indicated that the exchangeable Ca in these cells averages 25.7 +/-3.2nmol/mg protein, which represents approximately 9.8% of their ttotal Ca content. 2. Perifusion of 45Ca prelabelled fat cells gave washout curves whose analysis conformed with three kinetically distinct Ca pools (Fig. 1). The fast exchangeable pool (Compartment A) had an efflux rate constant of 0.193 +/-0. 013 min.-. The release of Ca from the second and thrid pools (Compartments B and C) was much slower with efflux rate constants of 0.032 +/-0.0018 min.-1 and 0.0042 +/- 0.0006 min.-1 respectively. Changing the Ca concentration in the perifusing medium modified the initial fast phase and its rate constant, while added dinitrophenol (DNP) inhibited the efflux rate from the later compartments...

Stimulation of brain adenylate cyclase activity by the undecapeptide substance P and its modulation by the calcium ion

Synthetic substance P stimulated adenylate cyclase activity in particulate preparations from rat and human brain. The concentration of substance P for half maximal stimulation in rat brain was 1.8-10-minus 7 M. The stimulatory effect of substance P on the rat brain adenylate cyclase activity was 88% compared with 48% by noradrenalin, 163% by prostaglandin E1 and 184% by prostaglandin E2. Both the basal and substance P-stimulated adenylate cyclase activity in rat brain were inhibited by concentration of Ca-2+ above 10-minus 6 M. The chelating agent ethyleneglycol-bis-(beta-aminoethylether)-N, N'-tetraacetic acid at a concentration of 0.1 mM reduced the basal adenylate cyclase activity by 64% and eliminated the substance P-stimulated activity. The inhibition by ethyleneglycol-bis-(beta-aminoethylether)-N, N'-tetraacetic acid was completely reversed by increasing concentrations of Ca-2+.

Calcium ion transport by pig erythrocyte membrane vesicles

Preincubating pig erythrocyte membranes with ATP enhances their ability to accumulate Ca(2+) against a concentration gradient. The extent of this increase is dependent on preincubation time over the period 0-60min. As the accessibility of outside membrane markers is decreased by preincubation and as accumulated Ca(2+) is not removed by EGTA [ethanedioxybis(ethylamine)tetra-acetate], it is suggested that ATP causes the formation of sealed inside-out vesicles which can transport Ca(2+) inward. The transport system requires ATP and Mg(2+) and exhibits an apparent dissociation constant for Ca(2+) of approx. 100mum. Since the dissociation constant for Ca(2+)-sensitive ATPase (adenosine triphosphatase) in these preparations is similar, it is concluded that this ATPase is responsible for Ca(2+) transport. Polyphosphoinositide concentrations are also increased during incubation with ATP; however, there is no change in their rate of synthesis or breakdown during Ca(2+) transport.