Asymmetric pore distribution and loss of membrane lipid in electroporated DOPC vesicles

An externally applied electric field across vesicles leads to transient per foration of the membrane. The distribution and lifetime of these pores was examined using 1,2-di-oleoyl-sn-glycero-3-phosphocholine (DOPC) phospholipi d vesicles using a standard fluorescent microscope. The vesicle membrane wa s stained with a fluorescent membrane dye, and upon field application, a si ngle membrane pore as large as similar to7 mum in diameter was observed at the vesicle membrane facing the negative electrode. At the anode-facing hem isphere, large and visible pores are seldom found, but formation of many sm all pores is implicated by the data. Analysis of pre- and post-field fluore scent vesicle images, as well as images from negatively stained electron mi crographs, indicate that pore formation is associated with a partial loss o f the phospholipid bilayer from the vesicle membrane. Up to similar to 14% of the membrane surface could be lost due to pore formation. Interestingly, despite a clear difference in the size distribution of the pores observed, the effective porous areas at both hemispheres was approximately equal. Ca 2+ influx measurements into perforated vesicles further showed that pores a re essentially resealed within similar to 165 ms after the pulse. The pore distribution found in this study is in line with an earlier hypothesis (E. Tekle, R. D. Astumian, and P. B. Chock, 1994, Proc. Natl. Acad. Sci. U.S.A. 91:11512-11516) of asymmetric pore distribution based on selective transpo rt of various fluorescent markers across electroporated membranes.