DIP PATCH-CLAMP CURRENTS SUGGEST ELECTRODIFFUSIVE TRANSPORT OF THE POLYELECTROLYTE DNA THROUGH LIPID BILAYERS

Planar lipid bilayers formed from monolayers of diphytanoyl lecithin ( DPhL) were found to interact with plasmid DNA (5.6 kbp; M(r) = 3.7 X 1 0(6)) leading to an increase in the conductance of the membrane. The a ssociation of DNA with a lipid bilayer greatly facilitates the transpo rt of the small ions of the main salt KCl. The appearance of long-live d current levels, for instance, of 27.6 pA at V-m = +60 mV membrane vo ltage, where the actual contact (adsorption) is electrophoretically en hanced, suggests a locally conductive DNA/lipid interaction zone where parts of the DNA strand may be transiently inserted in the bilayer, l eaving other parts of the DNA probably protruding out from the outer s urface of the bilayer. At V-m = -60 mV, where DNA can be electrophoret ically moved away from the membrane, the membrane current is practical ly zero. This current asymmetry is initially also observed at higher v oltages, for instance at 200 mV. However, if the voltage sign (V-m = 200 mV) is changed after a transient positive current (approximate to 15 pA) was observed, there is also now (at V-m = -200 mV) a finite neg ative current at the negative membrane voltage. Thus, it appears that at V-m = +200 mV the adsorbed parts of the polyelectrolyte DNA are not only transiently inserted in, but actually also electrophoretically p ulled through, the porous zones onto the other membrane side leaving t he bilayer structure basically intact. These data provide direct elect ric evidence for the electrophoretic transport of a highly charged and hydrated macromolecule, probably together with the associated gegen-i ons, through the thin hydrophobic film of the lipid bilayer.