Phosphoinositide metabolism and the morphology of human erythrocytes

Membrane-phorbol ester interactions monitored by circular dichroism

The interaction of phorbol 12,13-dibutyrate (PDBu), 12-O-retinoylphorbol 13-acetate (RPA) and 12-O-tetradecanoylphorbol 13-acetate (TPA) with L-alpha-phosphatidylserine-containing small unilamellar vesicles or erythrocyte ghosts was monitored by circular dichroism (CD). No change in the CD spectra of PDBu was observed upon binding, while RPA and TPA spectra were slowly affected by the interaction. The changes in RPA and TPA spectra were assigned to the embedding of these molecules in the membrane bilayers. In the presence of 10(8) cells/ml, after one minute incubation, about 2 to 5% of the amount of phorbol ester added is embedded in the membrane. It is suggested that either phorbol esters entering the membrane is not a prerequisite for protein kinase C activation or the amount of phorbol esters necessary to activate protein kinase C is very small.

"In situ" characterization of guanine nucleotide-binding properties of erythrocyte membranes

Unsealed membranes from human erythrocytes bind GTP and GTP analogs according to first order kinetics, a single rate constant being observed. With [35S]GTP gamma S this is 0.15 +/- 0.2 min-1. Treatment of the membranes with detergents decreases binding considerably. Scatchard plots reveal uncomplicated patterns of ligand association, with Kd values of 10.2 +/- 2.3 nM [35S]GTP gamma S, of 18.2 +/- 4.3 nM [alpha-32P]GTP and of 28.6 +/- 3.5 nM [alpha-32P]GDP, respectively. The stoichiometry with the three ligands is strictly comparable, i.e. 65 +/- 7 picomoles/mg of membrane protein. Binding of each labeled nucleotide is competitively inhibited by the other two unlabeled ligands, the inhibition constants being very close to the corresponding Kd values. Metabolic depletion and subsequent repletion of intact erythrocytes result in membrane preparations still active in guanine nucleotide binding, with unmodified Kd values. However, the stoichiometry falls to 35 picomoles/mg protein with the "depleted" erythrocyte membranes and regains higher values (50 picomoles/mg protein) with the "repleted" cell membranes. Accordingly, the "in situ" characterization of guanine nucleotide-binding properties of erythrocyte membranes seems to represent a new tool for monitoring the metabolic state of intact erythrocytes.

Binding of neomycin to phosphatidylinositol 4,5-bisphosphate (PIP2)

Schacht (Schacht, J. (1976) J. Neurochem. 27, 1119-1124) demonstrated that neomycin, an aminoglycoside antibiotic, binds with high affinity to phosphatidylinositol 4,5-bisphosphate (PIP2). We investigated the binding of neomycin to PIP2 by making electrophoretic mobility measurements with multilamellar bilayer vesicles and surface potential measurements with monolayers. The bilayers and monolayers were formed from mixtures of PIP2 and egg phosphatidylcholine (PC) in 0.1 M KCl at pH 7. Neomycin does not bind to PC; 10(-3) M neomycin affects neither the zeta potential of PC vesicles nor the surface potential of PC monolayers. In contrast, 10(-6) M neomycin reduces the magnitude of the zeta potential of PC/PIP2 vesicles (5, 9, and 17 mol% PIP2) and the surface potential of monolayers (17 mol% PIP2) to less than 50% of their initial values. The electrophoretic mobility results indicate that neomycin forms an electroneutral complex with PIP2; high concentrations (greater than 10(-4) M) of neomycin reduce the zeta potential of the PC/PIP2 vesicles to zero. We could describe our data with the Gouy-Chapman-Stern theory assuming the intrinsic association constant of the 1:1 neomycin-PIP2 complex is 10(5) M-1. Neomycin is widely used in cell biology to interfere with the generation of second messengers; we discuss the relevance of our results to these studies. Specifically, 10(-6) M neomycin binds greater than 50% of the PIP2 in a bilayer or monolayer but 10(-5)-10(-3) M neomycin is required to affect the turnover of PIP2 in permeabilized platelets, mast cells, and sea urchin eggs. This result is consistent with a hypothesis that most of the PIP2 in the inner leaflet of these plasma membranes is not accessible to neomycin because it is associated with proteins.

Volume-sensitive K influx in human red cell ghosts

K influx into resealed human red cell ghosts increases when the ghosts are swollen. The influx demonstrates properties similar to volume-sensitive K fluxes present in other cells. The influx is, for the most part, insensitive to the nature of the major intracellular cation and therefore is not a K-K exchange. The influx is much greater when the major anion is Cl than when the major anion is NO3; Cl stimulates the flux and, at constant Cl, NO3 inhibits it. Increase in the influx rate is rapid when shrunken ghosts are swollen or when NO3 is replaced by Cl. The volume-sensitive K influx requires intracellular MgATP at low concentrations, and ATP cannot be replaced by nonhydrolyzable ATP analogues. The volume-sensitive influx is inhibited by Mg2+ and by high concentrations of vanadate, but is stimulated by low concentrations of vanadate. It is not modified by cAMP, the removal of Ca2+ by EGTA, substances that activate protein kinase C, or by inhibition of phosphatidylinositol kinase. The influx is inhibited by neomycin and by trifluoperazine.

Interaction of adriamycin with human erythrocyte membranes. Role of the negatively charged phospholipids

The interaction of the antitumor compound adriamycin with human erythrocyte membranes, used as models of target cell membranes, has been studied using circular dichroism measurements. In order to elucidate the nature of the sites involved in the electrostatic interaction between adriamycin and erythrocyte membranes, its interaction with the following macromolecular systems was studied: phosphatidylserine-containing small unilamellar vesicles (SUV), prepared from total lipid extracts of erythrocytes, sialic acid-depleted erythrocyte ghosts and mucopolysaccharides. We have shown that the interaction between adriamycin and carboxylate groups is very weak and that negatively charged phosphate groups, in the case of membranes, or sulfate groups, in the case of mucopolysaccharides, are responsible for the prime interaction of adriamycin with these macromolecular systems.

Adsorption of cations to phosphatidylinositol 4,5-bisphosphate

We investigated the binding of physiologically and pharmacologically relevant ions to the phosphoinositides by making 31P NMR, electrophoretic mobility, surface potential, and calcium activity measurements. We studied the binding of protons to phosphatidylinositol 4,5-bisphosphate (PIP2) by measuring the effect of pH on the chemical shifts of the 31P NMR signals from the two monoester phosphate groups of PIP2. We studied the binding of potassium, calcium, magnesium, spermine, and gentamicin ions to the phosphoinositides by measuring the effect of these cations on the electrophoretic mobility of multilamellar vesicles formed from mixtures of phosphatidylcholine (PC) and either phosphatidylinositol, phosphatidylinositol 4-phosphate, or PIP2; the adsorption of these cations depends on the surface potential of the membrane and can be described qualitatively by combining the Gouy-Chapman theory with Langmuir adsorption isotherms. Monovalent anionic phospholipids, such as phosphatidylserine and phosphatidylinositol, produce a negative electrostatic potential at the cytoplasmic surface of plasma membranes of erythrocytes, platelets, and other cells. When the electrostatic potential at the surface of a PC/PIP2 bilayer membrane is -30 mV and the aqueous phase contains 0.1 M KCl at pH 7.0, PIP2 binds about one hydrogen and one potassium ion and has a net charge of about -3. Our mobility, surface potential, and electrode measurements suggest that a negligible fraction of the PIP2 molecules in a cell bind calcium ions, but a significant fraction may bind magnesium and spermine ions.

Erythrocytes attached to a wheat germ agglutinin coated surface display an altered phospholipid metabolism

Erythrocytes were bound to a lectin-coated surface; the multivalent attachment to this surface resulted in a severe deformation of the cells and an alteration in the cellular phospholipid metabolism. Human erythrocytes were allowed to bind for 20 min at 20 degrees C to polystyrene beads coated with wheat germ agglutinin (WGA beads). The bound erythrocytes were then lysed to produce stroma bound to WGA beads. Control stroma and stroma-WGA beads were incubated at 37 degrees C with gamma-32P-ATP to examine the phospholipid labeling patterns. The control stroma incorporated 32P-label into phosphatidylinositol-4-phosphate and phosphatidylinositol-4,5-bisphosphate, in agreement with earlier studies. However, the stroma-WGA beads showed incorporation of 32P-label into phosphatidic acid in addition to that in the phosphoinositides. The quantity of 32P-phosphatidic acid produced during the 20-min assay was 3.23 +/- 0.84 (n = 7) picomoles/micrograms stromal cholesterol; the amount synthesized, however, was dependent on the procedure used to prepare the stroma-WGA beads. If the erythrocytes were bound to the WGA beads at 0 degrees C instead of 20 degrees C, the quantity of 32P-phosphatidic acid produced during the subsequent 37 degrees C assay with gamma-32P-ATP was decreased 4.2 fold; the phosphoinositide labeling pattern was unchanged. In addition, when the time for binding of intact erythrocytes to the WGA beads was varied from 1 to 20 minutes, there was a time-dependent increase in the amount of 32P-phosphatidic acid produced. This induction of phosphatidic acid synthesis could not be duplicated with fluid phase WGA. Therefore, the multivalent binding of intact erythrocytes to WGA beads causes an alteration in phospholipid metabolism.

Influence of chlorpromazine on the transverse mobility of phospholipids in the human erythrocyte membrane: relation to shape changes

The influence of chlorpromazine (CPZ) on the transverse mobility of spin-labeled phospholipids incorporated into human erythrocytes was investigated by electron spin resonance. The very slow transverse diffusion of phosphatidylcholine, as well as the absence of transverse mobility of sphingomyelin were not modified even by sublytic concentrations (approximately equal to 1 mM) of CPZ. On the other hand, the rapid outside-inside translocation of the aminophospholipids (Seigneuret and Devaux (1984) Proc. Natl. Acad. Sci. USA 81, 3751-3755), was slightly hindered in CPZ containing membranes. If the spin-labeled aminolipids were incorporated in erythrocytes and allowed to flip to the inner monolayer before CPZ addition, a fraction of the spin labels (10-15%) flipped back instantaneously from the inner to the outer leaflet, upon incubation with CPZ. Similar experiments carried out with spin-labeled phosphatidylcholine and spin-labeled sphingomyelin showed that a fraction of the spin-labeled choline derivatives flip instantaneously to the inner leaflet if CPZ was added after the spin labels. Addition of lysophosphatidylcholine had no effect on the spin-labeled phospholipid redistribution nor on their transmembrane mobility. We interpret the immediate effect of CPZ addition as being due to a reorganization of the bilayer accompanying the rapid CPZ membrane penetration, phenomenon which is independent of the CPZ effect on the steady-state activity of the 'aminophospholipid translocase', the latter effect being probably a direct CPZ-protein interaction. By comparison of the time course of phosphatidylserine transverse diffusion in control discocyte cells and in CPZ-induced stomatocytes, we infer that the difference in cell shape is not a major factor in the regulation of the active inward transport of aminophospholipids in human erythrocytes.

Membrane bilayer balance and platelet shape: morphological and biochemical responses to amphipathic compounds

Activated platelets adopt a characteristic spiculate morphology. A wide variety of anionic and zwitterionic amphipathic compounds were found to effect a similar shape change and to cause the open canalicular system to become less prominent. Several cationic amphipaths reversed thrombin-, PAF-, and amphipath-induced spiculation and restored the discoid shape. Higher concentrations of cationic amphipaths caused the cells to assume spheroid and indented forms, and caused the canalicular system to appear more prominent. Three amphipaths were studied further to address possible mechanisms underlying their morphological effects. Dilauroylphosphatidylcholine was found to induce spiculation without causing the changes in protein phosphorylation and inositide metabolism generally associated with platelet activation. Two other amphipaths, chlorpromazine (which induced sphering) and dilauroylphosphatidylserine (which caused spiculation followed by sphering) caused specific changes in protein and/or lipid phosphorylation, which may be responsible for some, but not all, of the morphological effects of these compounds. To account for these findings, we propose that platelet shape can be influenced by changes in the plasma membrane bilayer balance. Agents that bind to the membrane outer monolayer are accommodated by spiculation; those that bind to the inner monolayer are accommodated by sphering.

Does phospholipase C inhibit fusion between hamster sperm and zona-free eggs?

Previous studies (Hirao and Yanagimachi: Gamete Res. 1:3-12, 1978) have found that phospholipase C (PLC) preparations inhibit sperm-egg fusion. We have attempted to duplicate these results with PLC, as well as with a more specific enzyme, phosphatidylinositol-specific PLC. PLC preparations were applied externally to zona-free hamster eggs prior to incubation with sperm. Phosphatidylinositol-specific PLC did not inhibit sperm penetration. The degree of sperm-egg fusion observed after egg exposure to PLC, however, was dependent upon the purity of the commercial preparation. An impure sample of PLC inhibited sperm penetration, while a more purified preparation did not. The morphology of eggs was unaffected by exposure to phosphatidylinositol-specific PLC and the more purified PLC preparation. The impure preparation, however, was disruptive primarily to the egg plasma membrane as well as to internal organelle organization. The degree of damage by the impure PLC preparation was concentration dependent. The results suggest that as purity of the PLC preparation is increased, the adverse effects of PLC on sperm-egg fusion become negligible.

Storage of human red blood cells and platelets. Some aspects concerning the factors leading to storage lesion characterized as morphological changes and vesiculation. Minireview based on a doctoral thesis

1. Storage renders erythrocytes more responsive to thermally induced morphological changes, especially the shedding of microvesicles. 4-8 week old cells can be morphologically "rejuvenated" by heating. 2. If pH increases during storage of platelets an extensive loss of small particles occurs. The platelet disintegration is associated with a loss in the metabolic activity, discharge of LDH, increased susceptibility to phospholipid hydrolysis by phospholipase C and is found to be initiated during the actual preparation of platelet concentrates. 3. Activation of platelets during preparation can be decreased by shortening the first centrifugation time or by using adenine in the anticoagulant. 4. A 4 hour prestorage of the whole blood unit prior to centrifugation strongly decreases the activation of platelets upon stimuli and results in platelet concentrates much more stable to storage.

Phagocytosis of in vitro-aged erythrocytes--a sharp distinction between activated and normal macrophages

Phagocytosis experiments performed in vitro in the absence of serum with mouse peritoneal macrophages have shown that normal macrophages can bind to in vitro-aged sheep red blood cells without antibody or complement, but only activated macrophages are able to ingest these erythrocytes. This sharp qualitative functional difference may be an index for the characterization of the activated state of macrophages.

Spin label study of erythrocyte deformability. Ca2+-induced loss of deformability and the effects of stomatocytogenic reagents on the deformability loss in human erythrocytes in shear flow

The Ca2+-induced loss of deformability in human erythrocytes and the recovery of the lost deformability by stomatocytogenic reagents were investigated by means of a new flow electron paramagnetic resonance (EPR) spin label method, which provides information on deformation and orientation characteristics of spin labeled erythrocytes in shear flow. The Ca2+-induced loss of deformability is attributed mainly to the increase in intracellular viscosity resulting from efflux of intracellular potassium ions and water (Gardos effect). Partial recovery of the lost deformability is demonstrated in the presence of stomatocytogenic reagents, such as chlorpromazine, trifluoperazine, W-7, and calmidazolium (R24571). The recovery can not be explained solely by suppression of the Gardos effect due to the reagents. Incorporation of an optimal amount of the reagents into the membrane appears to compensate for the membrane modification due to Ca2+ ions to restore a part of the lost deformability.

Multiple metabolic pools of phosphoinositides and phosphatidate in human erythrocytes incubated in a medium that permits rapid transmembrane exchange of phosphate

1. A Hepes-based medium has been devised which allows rapid Pi exchange across the plasma membrane of the human erythrocyte. This allows the metabolically labile phosphate pools of human erythrocytes to come to equilibrium with [32P]Pi in the medium after only 5 h in vitro. 2. After 5-7 h incubation with [32P]Pi in this medium, only three phospholipids, phosphatidic acid (PtdOH), phosphatidylinositol 4-phosphate (PtdIns4P) and phosphatidylinositol 4,5-bisphosphate (PtdIns4,5P2) are radioactively labelled. The concentrations of PtdIns4P and PtdIns4,5P2 remain constant throughout the incubation, so this labelling process is a reflection of the steady-state turnover of their monoester phosphate groups. 3. During such incubations, the specific radioactivities of the monoesterified phosphates of PtdIns4, PtdIns4,5P2 and PtdOH come to a steady value after 5 h that is only 25-30% of the specific radioactivity of the gamma-phosphate of ATP at that time. We suggest that this is a consequence of metabolic heterogeneity. This heterogeneity is not a result of the heterogeneous age distribution of the erythrocytes in human blood. Thus it appears that there is metabolic compartmentation of these lipids within cells, such that within a time-scale of a few hours only 25-30% of these three lipids are actively metabolized. 4. The phosphoinositidase C of intact human erythrocytes, when activated by Ca2+-ionophore treatment, only hydrolyses 50% of the total PtdIns4,5P2 and 50% of 32P-labelled PtdIns4,5P2 present in the cells: this enzyme does not discriminate between the metabolically active and inactive compartments of lipids in the erythrocyte membrane. Hence at least four metabolic pools of PtdIns4P and PtdIns4,5P2 are distinguishable in the human erythrocyte plasma membrane. 5. The mechanisms by which multiple non-mixing metabolic pools of PtdOH, PtdIns4P and PtdIns4,5P2 are sustained over many hours in the plasma membranes of intact erythrocytes are unknown, although some possible explanations are considered.

Influence of Ca2+ and Mg2+ on the turnover of the phosphomonoester group of phosphatidylinositol 4-phosphate in human erythrocyte membranes

In isolated erythrocyte membranes, increasing the free Mg2+ concentration from 0.5 to 10 mM progressively activates the membrane-bound phosphatidylinositol (PtdIns) kinase and leads to the establishment of a new equilibrium with higher phosphatidylinositol 4-phosphate (PtdIns4P) and lower PtdIns concentrations. The steady-state turnover of the phosphomonoester group of PtdIns4P also increases at high Mg2+ concentrations, indicating a simultaneous activation of PtdIns4P phosphomonoesterase by Mg2+. Half-maximum inhibition of PtdIns kinase occurs at 10 microM free Ca2+ in the presence of physiological free Mg2+ concentrations. Increasing free Mg2+ concentrations overcome Ca2+ inhibition of PtdIns kinase. In the presence of Ca2+, calmodulin activates Ca2+-transporting ATPase 5-fold, but does not alter pool size and radiolabelling of PtdIns4P. In intact erythrocytes, adding EGTA or EGTA plus Mg2+ and the ionophore A23187 to the external medium does not exert significant effects on concentration and radiolabelling of polyphosphoinositides when compared with controls in the presence of 1.4 mM free Ca2+.

Shape transformations induced by amphiphiles in erythrocytes

Shape alterations induced in human erythrocytes by cationic, anionic, zwitterionic and nonionic amphiphiles (C10-C16) at antihaemolytic concentrations (CAH50 and CAHmax) and at a slightly lytic concentration (2-10% haemolysis) were studied. Anionic (sodium alkyl sulphates) and zwitterionic amphiphiles (3-(alkyldimethylammonio)-1-propanesulfonates) proved to be potent echinocytogenic agents. Among the nonionic amphiphiles there were potent stomatocytogenicagents (octaethyleneglycol alkyl ethers, pentaethyleneglycol dodecyl ether), one potent echinocytogenic agent (dodecyl D-maltoside) and one weak echinocytogenic agent (decyl beta-D-glucopyranoside). Shape alterations induced by cationic amphiphiles (alkyltrimethylammonium bromides, cetylpyridinium chloride and dodecylamine hydrochloride) showed a strong time-dependence. These amphiphiles immediately induced strongly crenated erythrocytes which during incubation shifted to less crenated erythrocytes or to stomatocytes. All of the echinocytogenic amphiphiles induced echinocytes immediately, and there were only small alterations of the induced shape during incubation. Among the stomatocytogenic amphiphiles there were some that induced stomatocytes immediately or after a short lag time while others first passed the erythrocytes through echinocytic stages before stomatocytic shapes were attained. Erythrocytes treated with amphiphiles did not recover their normal discoid shape following repeated washing and reincubation for 1 h in amphiphile-free medium. Our study shows that shape alterations induced by amphiphiles in erythrocytes cannot be explained solely by assuming a selective intercalation of differently charged amphiphiles into the monolayers of the lipid bilayer as suggested in the bilayer couple hypothesis (Sheetz, M.P. and Singer, S.J. (1976) J. Cell Biol. 70, 247-251). We suggest that amphiphiles, when intercalated into the lipid bilayer, trigger a rapid formation of intrabilayer non-bilayer phases which protect the bilayer against a collapse and bring about a transbilayer redistribution of intercalated amphiphiles as well as of bilayer lipids.

Tyrosyl and phosphatidylinositol kinases of human erythrocyte membranes

The tyrosyl kinase and phosphatidylinositol (PI) kinase activities of human red cells have been partially purified and characterized. Although the PI kinase required detergent for solubilization, the major tyrosyl kinase of the red cell could be extracted by high salt. A very small residual activity remained associated with the membranes, however, that was solubilized with the PI kinase and copurified through an ammonium sulfate precipitation and diethylaminoethyl (DEAE) ion-exchange step gradient elution. However, the two activities were found to differ with respect to their apparent KmS for ATP and Mg2+; they showed different half-lives for temperature inactivation, possessed different relative activities in the presence of Mn2+ and Ca2+, and were separable by elution from a DEAE-Trisacryl ion exchange column using a linear NaCl gradient. The kinetic parameters of the membrane-associated tyrosyl kinase differed from those of the salt-extracted enzyme. PI kinase was not activated by pretreatment with the tyrosyl kinase p68v-ros or by addition of the phosphotyrosyl phosphatase inhibitor, vanadate, to intact membranes, and was not competitively inhibited by the tyrosyl kinase substrate poly(Glu4, Tyr). We conclude that the human red cell phosphatidylinositol and tyrosyl kinases are distinct and separate activities, and that at least two separable tyrosyl kinases are present in human erythrocytes.

The effect of phorbol esters on human erythrocyte morphological discocyte-echinocyte transitions

12-O-Tetradecanoylphorbol-13-acetate (TPA) (100 nM) when incubated with human erythrocytes under conditions of ATP depletion, delayed the onset of the morphological transition from discocytes to echinocytes so that at 2 h, when control incubations were estimated to contain 65% echinocytes, those treated with TPA contained 23% echinocytes. TPA did not alter the subsequent rate of the transition which was complete by 3 h in control cells and 5 h in TPA-treated cells. Addition of 100 nM TPA to ATP-depleted erythrocytes at 2.5 h (greater than 80% echinocytes) for 0.5 h at 37 degrees C resulted in 17% reversal to a discocyte morphology, but as the time of incubation under conditions of ATP depletion was extended, the level of the reversal fell. TPA had no significant effect on the fall in ATP concentrations over the time course of the experiments (5 h). Preincubation of discocytes with TPA for 10 min also prevented, by approx. 50%, the echinocytosis induced by the calcium (0.2 mM) loading of discocytes using 5 microM A23187. TPA was unable to reverse the echinocyte morphology of calcium-loaded cells back to discocytes. The less potent tumour promotor 4-phorbol-12,13-didecanoate had no effect on this discocyte-echinocyte transition. Incubation of discocytes with the diacylglycerol 1-oleoyl-2-acetylglycerol (OAG) (1-10 microM) had complex effects on morphology, and the ATP-induced morphological transition, ranging from stomatocyte formation to echinocyte formation, depending upon the concentration of the agent and the time of incubation.

Ethanol-induced alterations in human erythrocyte shape and surface properties: modulatory role of prostaglandin E1

Exposure of human erythrocytes to ethanol (1 to 20% by vol) in Ca2+ and Mg2+-free phosphate-buffered saline, pH 7.4, transformed biconcave discs into spiculated echinocytes within 3 min at 25 degrees C. The effects of ethanol were concentration-and time-dependent, but reversible by washing in the incubation buffer system within 60 min of initial exposure to ethanol. After prolonged ethanol exposure (180 min), washing of cells resulted in the formation of stomatocytes (cup-forms). Ethanol-induced echinocytosis was also accompanied by a 30% enhancement in the agglutinability of erythrocytes by ligands with high affinity for negative surface charge (poly-L-lysine and wheat germ agglutinin, 20 microliters/ml) without any alterations in surface charge topography. Concomitant exposure of erythrocytes to prostaglandin E1 (100 nM) selectively prevented the enhancement of ligand-mediated agglutinability, but did not modify cell shape. These data indicate that certain erythrocyte surface properties may not be directly influenced by cell shape and suggest a unique modulatory action of prostaglandin E1 on shape-transformed cells.

The molecular basis of erythrocyte shape

Recent discoveries about the molecular organization and physical properties of the mammalian erythrocyte membrane and its associated structural proteins can now be used to explain, and may eventually be used to predict, the shape of the erythrocyte. Such explanations are possible because the relatively few structural proteins of the erythrocyte are regularly distributed over the entire cytoplasmic surface of the cell membrane and because the well-understood topological associations of these proteins seem to be stable in comparison with the time required for the cell to change shape. These simplifications make the erythrocyte the first nonmuscle cell for which it will be possible to extend our knowledge of molecular interactions to the next hierarchical level of organization that deals with shape and shape transformations.

Separation of phosphoinositides and other phospholipids by two-dimensional thin-layer chromatography

A simple, rapid, two-dimensional TLC system is presented which resolves the four phosphoinositide cycle phospholipids as well as all commonly encountered major and minor phospholipids. Ca2+-free lipid samples are loaded onto silica gel HL plates and developed first in 48:40:7:5 chloroform:methanol:water:concentrated ammonia, and then in 55:25:5 chloroform:methanol:formic acid. The method was applied successfully to human erythrocytes, human platelets, and BL/VL3 murine lymphoma cells.

Permeability alterations and antihaemolysis induced by amphiphiles in human erythrocytes

In an attempt to define the parameters in amphiphilic molecules important for their interaction with the erythrocyte membrane, the effects of cationic, anionic, zwitterionic and nonionic amphiphilic agents (C10-C16) on osmotic fragility and transport of potassium and phosphate in human erythrocytes were studied. All the amphiphiles protected the erythrocytes against hypotonic haemolysis. Half-maximum protection occurred at a concentration which was about 15% of that inducing 50% haemolysis. The concentrations of amphiphiles required to induce protection or haemolysis were related to the length of the alkyl chain in a way indicating that a membrane/aqueous phase partition is the mechanism whereby the amphiphile monomers intercalate into the membrane. At antihaemolytic concentrations all the amphiphiles increased potassium efflux and passive potassium influx. The increase in the fluxes was about the same in both directions through the membrane and there were no clear differences in the effects of the different amphiphilic derivatives at equi-protecting concentrations. Active potassium influx was decreased by cationic, zwitterionic and non-ionic amphiphiles. The ability of the amphiphiles to inhibit the influx was not related to the length of the alkyl chain. Anionic amphiphiles had no or only a weak stimulatory effect on the influx. Phosphate efflux was reduced by all the amphiphiles. The inhibitory potency of the different amphiphiles decreased in the following order; anionic greater than zwitterionic, non-ionic greater than cationic. Short-chained amphiphiles were more potent inhibitors than long-chained. The possible participation of non-bilayer phases (mixed inverted micelles) in the intercalation of amphiphiles into the membrane is discussed.

Outside-inside translocation of aminophospholipids in the human erythrocyte membrane is mediated by a specific enzyme

When human erythrocytes are incubated with spin-labeled analogues of sphingomyelin, phosphatidylcholine, phosphatidylserine, or phosphatidylethanolamine, with a short beta chain (C5) bearing a doxyl group at the fourth carbon position, the labeled lipids incorporate readily in the outer monolayer. The incorporation is followed in fresh erythrocytes by a selective inward diffusion of the amino derivatives. This observation led us to postulate the existence of a selective ATP-dependent system that would flip aminophospholipids from the outer to the inner monolayer [Seigneuret, M., & Devaux, P. F. (1984) Proc. Natl. Acad. Sci. U.S.A. 81, 3751-3755]. This study further examines the nature of this selective transport and demonstrates that it is mediated by a specific membrane protein. By measurement of the initial rate of transverse diffusion of spin-labeled lipids incorporated at various concentrations in the membrane outer leaflet of packed erythrocytes, apparent Km values were determined for the phosphatidylserine and phosphatidylethanolamine analogues. A ratio of approximately equal to 1/9.4 [corrected] was obtained (KmPS/KmPE). Using spin-labels bearing either a 14N or a 15N isotope, we have carried out competition experiments allowing us to measure simultaneously the transport of two different phospholipids. By this procedure, we show that phosphatidylserine and phosphatidylethanolamine compete for the same transport site but that phosphatidylserine has a higher affinity, in agreement with a lower apparent Km. On the other hand, the slow diffusion of the phosphatidylcholine or sphingomyelin analogues has no influence on the transport of phosphatidylserine or phosphatidylethanolamine. Experiments carried out in ghosts loaded with ATP enabled us to determine the activation energies for phosphatidylserine and phosphatidylcholine transverse diffusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in membrane polypeptides, polyphosphoinositides and phosphatidate in dense fractions of sickle cells

When sickle erythrocytes were fractionated on discontinuous isotonic stractan gradients the denser fractions, which were rich in irreversibly sickled cells contained less polyphosphoinositides and more phosphatidate than either lighter sickle cell fractions or normal cells. These changes could be due to activation of a polyphosphoinositide phosphodiesterase in the denser cells. Membrane polypeptide analysis of the denser fractions also showed a marked depletion of band 4.1 and a protein of molecular mass about 110 kDa but an increased amount of a 180 kDa polypeptide which might be a breakdown product of ankyrin. These biochemical alterations could be consequences of Ca2+ accumulation in the denser sickle cells and may contribute to the structural alterations which give rise to irreversibly sickled cells.

[Energy-dependent translocation of amino-phospholipids in the erythrocyte membrane]

In this review, we show how the stability of the asymmetric transverse distribution of phospholipids and the physiological role of the asymmetric distribution can be explained. Experiments with paramagnetic or fluorescent lipids enabled us to show that in fresh red blood cells, i.e. containing ATP, and in resealed ghosts containing ATP (1 mM) the amino derivatives (phosphatidylserine and phosphatidylethanolamine) are selectively transported from the outer monolayer to the inner monolayer of the membranes. On the other hand, phosphatidylcholine and sphingomyelin are not carried and diffuse spontaneously with a very long characteristic time. The ATP-dependent carrier mechanism can be inhibited by protein reacting groups (N-ethyl maleimide and ortho-vanadate), which very probably implies a transmembrane protein specific for amino phospholipids. The affinity for phosphatidylserine seems slightly higher than that for phosphatidylethanolamine. In addition we show the close parallel between the transverse distribution of phospholipids and cell shape. This leads us to suggest that the phospholipid translocation would be used to maintain the natural discoid shape of red blood cells. A possible generalisation of this mechanism to other cells and its implications for endocytosis are discussed.

An actomyosin contractile mechanism for erythrocyte shape transformations

The membrane skeleton of the human erythrocyte consists of many short actin filaments that are multiply cross-linked by long, flexible spectrin molecules into a continuous network in the plane of the membrane. The mechanical properties expected for this spectrin-actin network can account for the tensile strength of the erythrocyte membrane and for the remarkable deformability of the cells, yet not for their characteristic biconcave shape. Recently, an authentic vertebrate myosin as well as a non-muscle form of tropomyosin have been identified and purified from erythrocytes. The myosin is present with respect to the actin in an amount comparable to actin-myosin ratios in other non-muscle cells, and there is enough tropomyosin to almost completely coat all of the short actin filaments in the membrane skeleton. The implications of these unexpected discoveries for the molecular organization of the cytoskeleton are discussed, and a mechanism is proposed by which myosin could interact with the membrane-associated actin filaments to influence erythrocyte shape and membrane properties.

The effect of dietary lipids on the trout erythrocyte membrane

Rainbow trout were fed either a commercial diet or semi-purified diets containing 8% by weight of either cod liver oil, grape seed oil or hydrogenated coconut oil. Important changes in the fatty acid composition of erythrocyte membrane phospholipids were induced by these dietary fats. No changes were seen in the cholesterol/phospholipid ratio and in the cellular ATP level. Shape changes (crenation of cell margin and shrinkage) were only seen in trout fed hydrogenated coconut oil in connection with an accumulation of high amounts of (n-9) fatty acids including 20:3 (n-9) phospholipids. The compositional changes affect the stability of the erythrocyte membrane. An increased rate of osmotic hemolysis appeared to be associated with an increased unsaturated fatty acid content of the membranes.

Phosphatidylinositol 4-phosphate kinase is associated with the membrane skeleton in human erythrocytes

Phosphatidylinositol 4-phosphate kinase was eluted from human erythrocyte stroma by three separate and distinct techniques which are known to disrupt the membrane skeleton. In addition, this kinase was found to be associated with the intact skeletons prepared by Triton X-100 extraction of stroma. Phosphatidylinositol 4-phosphate kinase which has been extracted from the membrane is a freely soluble protein with poor enzymatic activity toward added phosphatidylinositol-4-phosphate; however, the enzyme was shown to reassociate with skeleton-depleted stroma and then regain full enzymatic activity toward stromal bound substrate.

Regulation of the association of membrane skeletal protein 4.1 with glycophorin by a polyphosphoinositide

Many of the physical properties of the erythrocyte membrane appear to depend on the membrane skeleton, which is attached to the membrane through associations with transmembrane proteins. A membrane skeletal protein, protein 4.1, is pivotal in the assembly of the membrane skeleton because of its ability to promote associations between spectrin and actin. Protein 4.1 also binds to the membrane through at least two sites: a high-affinity site on the glycophorins and a site of lower affinity associated with band 3 (ref. 11). The glycophorin-protein 4.1 association has been proposed to be involved in maintenance of cell shape. Here we show that the association between glycophorin and protein 4.1 is regulated by a polyphosphoinositide cofactor. This observation suggests a mechanism which may explain the recently reported dependence of red cell shape on the level of polyphosphoinositides in the membrane.

The membrane skeleton of a unicellular organism consists of bridged, articulating strips

In this paper we show that a membrane skeleton associated with the plasma membrane of the unicellular organism Euglena consists of approximately 40 individual S-shaped strips that overlap along their lateral margins. The region of strip overlap is occupied by a set of microtubule-associated bridges and microtubule-independent bridges. Both cell form and plasma membrane organization are dependent on the integrity of this membrane skeleton. Removal of the membrane skeleton with a low-molar base results in loss of membrane form and randomization of the paracrystalline membrane interior characteristic of untreated cells. Conversely, removal of the plasma membrane and residual cytoplasm with lithium 3,5-diiodosalicylate/Nonidet P-40 yields cell ghosts that retain the form of the original cell but consist only of the membrane skeleton. Two major polypeptides of 86 and 80 KD persist in the skeleton and two other major proteins of 68 and 39 kD are associated with the plasma membrane fraction. None of these components appears to be the same as the major polypeptides (spectrins, band 3) of the erythrocyte ghost, the other cell system in which a well-defined peripheral membrane skeleton has been identified. We suggest that the articulating strips of euglenoids are not only the basic unit of cell and surface form, but that they are also positioned to mediate or accommodate surface movements by sliding, and to permit surface replication by intussusception.

Lipid molecular shape affects erythrocyte morphology: a study involving replacement of native phosphatidylcholine with different species followed by treatment of cells with sphingomyelinase C or phospholipase A2

In a previous report it was shown that the replacement of native erythrocyte phosphatidylcholine (PC) with different PC species which have defined acyl chain compositions can lead to morphological changes (Kuypers, F.A., W. Berendsen, B. Roelofsen, J. A. F. Op den Kamp, and L.L.M. van Deenen, 1984, J. Cell Biol., 99:2260-2267). It was proposed that differences in molecular shape between the introduced PC species and normal erythrocyte PC caused the membrane to bend outwards or inwards, depending on the shape of the PC exchanged. To support this proposal, two requirements would have to be fulfilled: the exchange reaction would take place only with the outer lipid monolayer of the erythrocyte, and the extent of lipid transbilayer movement would be restricted. If this theory is correct, any treatment causing unilateral changes in lipid molecular shape should lead to predictable morphological changes. Since this hypothesis is a refinement of the coupled bilayer hypothesis, but so far lacks experimental support, we have sought other means to change lipid molecular shape unilaterally. Shape changes of human erythrocytes were induced by the replacement of native PC by various PC species using a phosphatidylcholine-specific transfer protein: by hydrolysis of phospholipids in intact cells using sphingomyelinase C or phospholipase A2, and by the combination of both procedures. The morphological changes were predictable; additive when both treatments were applied, and explicable on the basis of the geometry of the lipid molecules involved. The results strongly support the notion that lipid molecular shape affects erythrocyte morphology.

Ca2+-induced polyphosphoinositide breakdown due to phosphomonoesterase activity in chicken erythrocytes

Treatment of chicken erythrocytes with ionophore A23187 and Ca2+ caused the breakdown of a large proportion of the cellular polyphosphoinositides. Since no diacylglycerol or phosphatidate was generated, but there was a small increase in the level of phosphatidylinositol, it was concluded that breakdown occurred as a result of phosphomonoesterase activation. Experiments with subcellular fractions showed that the phosphomonoesterase activity was present in the cytosolic fraction of the cells.

Incorporation and translocation of aminophospholipids in human erythrocytes

Cell morphology changes are used to examine the interaction of exogenous phosphatidylserine and phosphatidylethanolamine with human erythrocytes. Short-chain saturated lipids transfer from liposomes to cells, inducing shape changes that are indicative of their incorporation into, and in some cases translocation across, the cell membrane bilayer. Dioleoylphosphatidylserine and low concentrations of dilauroyl- and dimyristoylphosphatidylserine induce stomatocytosis. At higher concentrations, dilauroylphosphatidylserine and dimyristoylphosphatidylserine induce a biphasic shape change: the cells crenate initially but rapidly revert to a discocytic and eventually stomatocytic shape. The extent of these shape changes is dose dependent and increases with increasing hydrophilicity of the phospholipid. Cells treated with dilauroylphosphatidylethanolamine and bovine brain lysophosphatidylserine exhibit a similar biphasic shape change but revert to discocytes rather than stomatocytes. These shape changes are not a result of vesicle--cell fusion nor can they be accounted for by cholesterol depletion. The reversion from crenated to stomatocytic forms is dependent on intracellular ATP and Mg2+ concentrations and the state of protein sulfhydryl groups. The present results are consistent with the existence of a Mg2+- and ATP-dependent protein in erythrocytes that selectively translocates aminophospholipids to the membrane inner monolayer engendering aminophospholipid asymmetry.

Polyphosphoinositides and the shape of mammalian erythrocytes

The relationship between polyphosphoinositide and phosphatidic acid (PA) metabolism and Mg-ATP dependent shape and viscosity changes in erythrocyte ghosts from four mammalian species was examined. Ghosts prepared from rabbit, dog, human and guinea pig erythrocytes were transformed from echinocytes to discocytes within 15 min in the presence of 1 mM Mg-ATP at 25 C. In all species these Mg-ATP shape transformations were associated with a 30-45% decrease in the specific viscosity of the ghost suspensions. Mg-ATP induced a second transformation of discocytic ghosts to cup shape forms without a further decrease in viscosity. A considerable species variation in the rates of Mg-ATP dependent viscosity and shape changes and incorporation of 32P into phosphatidylinositol-4' phosphate (PIP), phosphatidylinositol-4'5'bisphosphate (PIP2) and especially PA from Mg-[gamma 32P]-ATP in ghosts was found. However, the rates of Mg-ATP dependent synthesis of PIP and PIP2 and shape and viscosity changes in each species were of the same magnitude. Ca2+ or neomycin strongly inhibited PIP labeling and Mg-ATP shape and viscosity changes in ghosts of the different species. Ca2+ or neomycin usually increased or had little effect on 32P incorporation into PA and PIP2. The possibility that Mg-ATP-induced changes in erythrocyte membrane shape and deformability are dependent on increases in membrane PIP and PIP2 is discussed.

Impairment of the calcium pump of human erythrocytes by divicine

Divicine (2,6-diamino-4,5-dihydroxypyrimidine), an aglycone implicated in the pathogenesis of favism, produces a remarkable and consistent inactivation of the Ca2+-ATPase activity of the erythrocyte calcium pump. The patterns of inactivation are similar in normal and glucose-6-phosphate dehydrogenase (G6PD)-deficient erythrocytes. Inactivation of Ca2+-ATPase is apparently unrelated to the cellular GSH system, to the proteolytic machinery of mature erythrocytes, and to calmodulin, and also occurs in hemoglobin-free, unsealed erythrocytes membranes at 50-100 microM concentrations of divicine. Analysis of erythrocytes that have escaped destruction during the acute hemolytic crisis of a number of favic patients revealed a dramatic elevation of erythrocyte calcium and a significant decrease of Ca2+-ATPase activity. These results support the view that divicine plays a toxic role in the pathogenesis of favism and suggest that acute electrolyte imbalances, mostly affecting calcium homeostasis, are involved in the mechanisms of erythrocyte damage and destruction in this hemolytic disease.

Subcellular localisation of inositol lipid kinases in rat liver

The subcellular distribution of the enzymes which phosphorylate phosphatidylinositol sequentially to form phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate was investigated in rat liver. We demonstrate that whilst phosphatidylinositol kinase is present in Golgi, lysosomes and plasma membranes, the kinase that forms phosphatidylinositol 4,5-bisphosphate is localised predominantly at the plasma membrane. The role of the inositol lipid kinases in cell function is discussed.

Interaction of the antibiotic adriamycin with the plasma membrane

The antitumor antibiotic adriamycin was found to be a potent modulator of the human erythrocyte discocyte echinocyte transition. Incubation of discocytes for 10 min with 10 microM adriamycin inhibited calcium-induced echinocytosis by 90 per cent. Adriamycin itself had no effect on erythrocyte morphology, a feature which distinguished it from other amphipaths which bring about the formation of a cupped cell morphology. Additionally, adriamycin differed from amphipaths such as the phenothiazines in that concentrations which prevented echinocytosis had no effects on calmodulin, as measured by effects on calmodulin-stimulated 45Ca2+ uptake into inside-out red cell vesicles. Adriamycin, paradoxically, appeared to cause a fall in the levels of erythrocyte polyphosphoinositides, but prevented further breakdown induced by calcium loading. This fall in inositides may be apparent rather than real, as the drug did not cause breakdown of the inositides to either inositol di- or triphosphates in red cell vesicles. Instead, it inhibited breakdown. It is possible that adriamycin may complex out the inositides and thus maintain levels of the inositide polyphosphates, congruent with the maintenance of the discocyte morphology. Interference with inositol lipid metabolism may be an important aspect of the pharmacology of adriamycin.

Regulation of plasma membrane Ca2+ ATPases by lipids of the phosphatidylinositol cycle

When the erythrocyte plasma membrane Ca2+ pump is reconstituted into phosphatidylcholine liposomes, the inclusion of small amounts of phosphatidic acid or phosphatidylinositol 4,5-bisphosphate stimulates the enzyme's activity. Other lipids of the phosphatidylinositol cycle (diacylglycerol, phosphatidylinositol) have little effect. The stimulatory effect of phosphatidylinositol 4,5-bisphosphate is greater than that of calmodulin; this lipid also stimulates the plasma membrane Ca2+ ATPase from rat brain.