Cell fusion generates an inhomogeneous distribution of elasticity and rigidity in plasma membranes

The post-electrofusion oscillation cycle of human erythrocytes (doublets) was evaluated for the first four pump events in order to quantify the spectrin-network rearrangement in the fusion zone. Experiments were carried out on control cells and on cells that received a 40 degree C and a 45 degree C 20-min heat treatment. The amplitude of the geometrical changes depended on the heat-treatment procedure, whereas the roundness on entering the pump event was always identical. The rigid influence of the fusion zone prevented the doublets from adopting a spherical shape. The fusion zone was characterized by a linear elongation modulus that could be calculated from geometrical measurements and earlier findings on erythrocyte membrane mechanics, and that ranged between 1.44E6 Nm(-2) for control doublets and 0.99E6 Nm(-2) after 45 degrees C heat treatment. The membrane composition of the fusion zone differs greatly from that of the other membrane parts not involved in fusion processes and evidence is given that this inhomogeneity stems from a rearrangement of the triangulated spectrin network and other membrane skeletal proteins in the fusion zone.