The Copolymer Surfactant P188 Reduces Tension in Permeabilized Cell Membranes

Abstract

Introduction: Certain biocompatible block copolymer surfactants have been found to have important cytoprotective membrane sealing properties. Resealing of disrupted cell membranes through normal cellular endogenous vesicle- membrane fusion pathways is preceeded by a decrease in membrane line tension. It has been postulated that a similar decrease in membrane line tension preceeds sealing of permeabilized cell membranes by block copolymer surfactants such as Poloxamer 188 (P188). Methods: To test this concept we measured effects of sub-CMC P188 on line-tension in saponin permeabilized plasma membranes of MDCK cells in monolayer cell culture. 10 kDa neutral dextran was used an osmotic control. By recording quasi-static strain laser optical tweezer distraction of membrane-bound antibody coated latex 0.5μm diameter beads, we measured maximum tether length of detergent (0.005% saponin) disrupted MDCK cell membranes before and after treatment with either 0.2mM P188 or 0.2mM 10kDa neutral dextran (ND). Bead selection was determined by position and traction was parallel to cytoskeletal protein orientation. Steady-state tether length for maximum traction force was compared. Results and Discussion: Maximum tether length reflects available membrane reservoir and membrane material properties. Recorded tether lengths were 18.30±2.02 (mean±s.e.m.) μm for normal control cells. 6.46±0.82 μm for cells permeabilized with saponin, 6.18x0.96 μm for permeabilized cells treated with ND, and 11.09±1.09 μm for permeabilized cells treate with P188. Saponin extraction of membrane lipid increases membrane stiffness by reducing reservoir size and creation of water-filled defects.Because it is unlikely that P188 restores membrane reservoir volume, these results suggest P188 reduced membrane tension by resealing water-filled defects.