EFFECTS OF POLYOXYETHYLENE CHAIN-LENGTH ON ERYTHROCYTE HEMOLYSIS INDUCED BY POLY[OXYETHYLENE(N)NONYLPHENOL] NONIONIC SURFACTANTS

The effects of three different poly[oxyethylene (n) nonylphenols], n = 9.5, 20 and 100 oxyethylene (EO) units, on erythrocyte hemolysis and on the fluidity of the erythrocyte membrane were studied. The three di fferent surfactants showed different effects. The surfactant with aver age n = 9.5 EO units (C9E9) shows a biphasic effect: at low concentrat ions it protects erythrocytes against hypotonic hemolysis, but at high er concentrations it induces hemolysis both in isotonic and hypotonic buffers. C9E20 does not affect the erythrocyte membrane resistance to hemolysis, independent of the buffer osmolarity; this detergent did no t show a hemolytic effect. C9E100 is an effective protective agent aga inst hypotonic hemolysis, in concentrations > 2 x 10(-4) M. EPR spectr oscopy of spin-labeled stearic acid indicated that the three different surfactants increase the fluidity of erythrocyte ghost membranes. At the higher C9E20 and C9E100 surfactant concentrations in the presence of membrane ghosts, spin-label is located in the surfactant micelles. In the case of the hemolytic concentrations of C9E9, mixed (surfactant plus phospholipid) micelles are formed. These results suggest that C9 E9 has a higher affinity for membrane phospholipids, which accounts fo r its lytic activity. The protective effect of C9E100 is assigned to t he osmotic buffering of the liquid surrounding the cell membrane, due to the large polar chains anchored to the membrane outer monolayer but other mechanisms previously considered in the literature may also be effective. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.