SELECTIVE AND ASYMMETRIC MOLECULAR-TRANSPORT ACROSS ELECTROPORATED CELL-MEMBRANES

Transport of a divalent cation (Ca2+) and three DNA indicators [ethidi um bromide (EB), propidium iodide (Pr), and ethidium homodimer (EthD-1 )] across electroporated membranes of several mammalian cell lines was found to be selective and asymmetrical. In low salt medium, Ca2+ and EB were preferentially transported across the anodefacing cell membran e while PI and EthD-1 predominately entered at the site facing the cat hode. In high salt medium, the entry site for Ca2+ and EB was reversed to the cathode-facing hemisphere while it remained unchanged for PI a nd EthD-1. In all these experiments, the observed transport patterns r emained unaffected whether the dyes (or ion) were present during or ad ded after the electroporating pulse. The data suggest that asymmetric pores are created on both sides of the membrane facing the electrodes, with smaller pore size (but greater in number) on the anode side and larger pores (with a lower population) on the cathode side. Furthermor e, the rate of resealing of the membrane pores is significantly enhanc ed in high ionic strength medium, thus affecting the entry site. The a symmetric transport pattern is neither caused by electrophoresis induc ed by the externally applied electric field nor due to one-sided membr ane breakdown as previously believed.