Poly(ethylene glycol), surface potential and cell fusion

Abstract

Poly(ethylene glycol), glycerol and dimethyl sulphoxide markedly decrease the surface potentials of monolayers of phosphatidylcholine and phosphatidylethanolamine. This finding is discussed in relation to the properties of hen erythrocytes undergoing fusion induced by poly(ethylene glycol).Poly(ethylene glycol)-6000 induces the fusion of plant protoplasts (Kao & Michayluk, 1974), hen erythrocytes (Ahkong et al., 1975a), hen erythrocytes with yeast protoplasts (Ahkong et al., 1975b), and mammalian cells (Pontecorvo, 1975). We have studied the actions on monolayers of phospholipids of poly(ethylene glycol), glycerol, sorbitol, sucrose and dimethyl sulphoxide, all of which fuse hen ,erythrocytes (Ahkong et al., 1975a), to obtain information relevant to the molecular mechanisms by which these molecules may induce cell fusion. Materials and MethodsAnalaR NaCl, sucrose, sorbitol, glycerol, poly-(ethylene glycol) mol.wt. 1500 and poly(ethylene oxide) mol.wts. 3 x 105 and 5 x 106 were from BDH Chemicals, Poole, Dorset, U.K. Poly(ethylene glycol) and poly(ethylene oxide) describe the same polymer, -[CH2-CH2-0]"-, prepared from different monomers. The term poly(ethylene glycol) is used in this present paper, individual polymers being identified by their molecular weight. Dimethyl sulphoxide was from Sigma (London) Chemical Co., London S.W.6, U.K. Dipalmitoylglycerylphosphorylcholine, dipalmitoylglycerylphosphorylethanolamine and poly(ethylene glycol) mol.wt. 6000 were from Koch-Light Laboratories, Colnbrook, Bucks., U.K. Phospholipid monolayers were prepared from solutions in chloroform, and the surface pressures, molecular areas and surface potentials of the monolayers were recorded automatically, as described previously (Maggo & Lucy, 1975, 1976. All subphases contained NaCl (145mM); their pH was adjusted to 5.6 with HCI (5M) or NaOH (5M). The surface potential and surface pressure of each subphase were adjusted to give a zero reading before spreading of the phos. pholipid monolayer. Isotherms were obtained in duplicate; they were usually reproducible within * Present address: Departmento de Quimica Biologica, Universidad Nacional de Cordoba, Argentina. Vol. 158 ±0.02nm2, +lmN*m1l (+ldyn-cm-1) and ±lOmV. For some subphases containing high concentrations of organic solute, reproducibility was not better than 0.04nm2 in molecular areas, +2mN m-1 in surface pressure and ±20mV in surface potential; the isotherm was then obtained in triplicate, and the curves were averaged.Hen erythrocytes were prepared for experiments on cell fusion as described previously (Ahkong et al., 1973). ResultsPhospholipid monolayers Fig. 1 shows the surface potential-area and surface pressure-area curves for monolayers of phosphatidylcholine and phosphatidylethanolamine on subphases containing two small organic solutes and two polymers. Comparable observations (not shown) were made with subphases contaiing the other small organic solutes and polymers studied (see the Materials and Methods section). With subphases containing lower concentrations ...

Induction of membrane fusion by polysialogangliosides

“…In a case in which 3.3 mM Na2EDTA was present in the medium, the addition of glyceryl mono-oleate or GDa induced the appearance of rounded cells or of crenated or oddlyshaped cells, respectively, but neither membrane pinching off nor multinucleated cells were found. These observations indicate that as with other fusogenic agents [4][5][6] free Ca 2÷ is required for the ganglioside-induced fusion process.…”

“…Conversely, lipids chemically similar to those but not showing these type of interactions are ineffective as fusogenics [2,3]. On this basis it was surmised that a reduction of the electrostatic field perpendicular to the surface of the lipid bilayer induced by a lipid or a water-soluble substance is a key event for the initial increase of the membrane permeability and aggregation that leads to membrane fusion [6,7].…”

Water and calcium ions in cell fusion induced by poly(ethylene glycol)

“…The cells exhibited an abnormal permeability to Ca2+ cnly after treatment with concentrations of PEG that were >30% w/w, i.e., only after treatment with fusogenic concentrations of PEG. Above this concentration PEG-4000 and -6000 induced cell fusion, but PEG-l 500 which is less fusogenic with erythrocytes [9] did not. Cell fusion was always preceded by the entry of Ca2+ into the erythrocytes.…”

Polyethylene glycols interact with membrane glycerophospholipids: is this part of their mechanism for hypothermic graft protection?

“…This apparent stabilization of the lipid monolayer in the gaseous state, already described by Maggio et al [20], occurred only when intermolecular interactions between the acyl chains were weak (at low surface pressures).…”