• Spatial and temporal development of membrane fusion sites in response to a transmembrane electric field pulse

      Wu, Yankuan; Sowers, Arthur E. (1992)
      Cell fusion takes place when two cells become one larger cell. On a morphological level, this process appears as two spheres come into contact and then, after "membrane fusion", form an "hourglass" shape. As cell fusion continues to take place, the diameter of the hourglass "constriction"--or fusion zone--increases until the two separate cells become indistinguishable and one giant cell is formed. In the present work, this process was modeled using erythrocyte ghost membranes and an electric field protocol to induce fusion. It was found that: (1) The fusion zone can be either: (i) the "flat diaphragm" type, or (ii) the "open lumen" type, which of these occurs is dependent on whether the ghost membranes were heat-treated (42 {dollar}\sp\circ{dollar}C, 20 mins). (2) The fusion zone diameter vs. time relationship had three distinct kinetic components, and each was independently alterable by specific physico-chemical conditions. However, the duration of each component was always constant (Phase I = 1 sec, Phase II = 4 sec, Phase III = at least 120 sec). (3) Open lumen-type fusion zones were always produced from flat diaphragm fusion zones. In other words, the flat diaphragm "appeared", by phase optics, to "dissolve" in a gradual manner into an open lumen at a time which can be from 0.5 to 140 sec after membrane fusion is induced. The interval over which the flat diaphragm clearly exists is termed the flat diaphragm lifetime, and itself depends on specific physico-chemical conditions. (4) Under certain physico-chemical conditions, populations of fusion zones were found to be a heterogeneous mixture of flat diaphragm-type and open lumen-type. Additional factors have been identified which control the ratio of open lumens to flat diaphragms. (5) The complex dependence of the diameter vs. time response, the flat diaphragm lifetime, and the ratio of open lumens to flat diaphragms suggests that multiple but specific factors control spectrin-membrane mechano-functions at the molecular level. (6) Crossing the known spectrin calorimetric transition, which affects spectrin and only spectrin, during the heat treatment caused both the Phase II and the Phase III kinetic components to disappear.