STUDIES OF CELL PELLETS .2. OSMOTIC PROPERTIES, ELECTROPORATION, AND RELATED PHENOMENA - MEMBRANE INTERACTIONS

Using the relations between pellet structure and electric properties d erived from the preceding paper, the responses of rabbit erythrocyte p ellets to osmotic or colloidal-osmotic effects from exchanged supernat ants and from electroporation were investigated. Changing the ionic st rength of the supernatant, or replacing it with dextran or poly(ethyle ne glycol) solutions, caused changes of R(p) according to the osmotic behavior of the pellet. R(p) was high and ohmic before electroporation , but dropped abruptly in the first few microseconds once the transmem brane voltage exceeded the membrane breakdown potential. After the ini tial drop, R(p) increased as a result of the reduction of intercellula r space. R(p) increased regardless of whether the pellets were formed before or immediately after the pulse, indicating that porated cells e xperienced a slow colloidal-osmotic swelling. The intercellular or int ermembrane distances between cells in a pellet, as a function of osmot ic, colloidal-osmotic, and centrifugal pressures used to compress rabb it erythrocyte pellets, were deduced from the R(p) measurement. This o ffered a unique opportunity to measure the intermembrane repulsive for ce in a disordered system including living cells. Electrohemolysis of pelleted cells was reduced because of limited swelling by the compactn ess of the pellet. Electrofusion was observed when the applied voltage per pellet membrane exceeded the breakdown voltage. The fusion yield was independent of pulse length greater than 10 mu s, because after th e breakdown of membrane resistance, voltage drop across the pellet bec ame insignificant. Replacing the supernatant with poly(ethylene glycol ) or dextran solutions, or coating pellets with unporated cell layers reduced the colloidal osmotic swelling and hemolysis, but also reduced the electrofusion yield. These manipulations can be explored to incre ase electroloading and electrofusion efficiencies.