POLOXAMER-188 DECREASES SUSCEPTIBILITY OF ARTIFICIAL LIPID-MEMBRANES TO ELECTROPORATION

The effect of a nontoxic, nonionic block cc-polymeric surface active a gent, poloxamer 188, on electroporation of artificial lipid membranes made of azolectin, was investigated. Two different experimental protoc ols were used in our study: charge pulse and Voltage clamp. For the ch arge pulse protocol, membranes were pulsed with a 10-mu S rectangular voltage waveform, after which membrane Voltage decay was observed thro ugh an external 1-M Ohm resistance. For the voltage clamp protocol the membranes were pulsed with a waveform that consisted of an initial 10 -mu s rectangular phase, followed by a negative sloped ramp that decay ed to zero in the subsequent 500 mu s. Several parameters characterizi ng the electroporation process were measured and compared for the cont rol membranes and membranes treated with 1.0 mM poloxamer 188. For bot h the charge pulse and voltage clamp experiments, the threshold voltag e (amplitude of initial rectangular phase) and latency time (time elap sed between the end of rectangular phase and the onset of membrane ele ctroporation) were measured. Membrane conductance (measured 200 mu s a fter the initial rectangular phase) and rise time (t; the time require d for the porated membrane to reach a certain conductance value) were also determined for the voltage clamp experiments, and postelectropora tion time constant (PE tau; the time constant for transmembrane Voltag e decay after onset of electroporation) for the charge pulse experimen ts. The charge pulse experiments were performed on 23 membranes with 1 0 control and 13 poloxamer-treated membranes, and voltage pulse experi ments on 49 membranes with 26 control and 23 poloxamer-treated membran es: For both charge pulse and voltage clamp experiments, poloxamer 188 -treated membranes exhibited a statistically higher threshold voltage (p = 0.1 and p = 0.06, respectively), and longer latency time (p = 0.0 4 and p = 0.05, respectively). Also, poloxamer 188-treated membranes w ere found to have a relatively lower conductance (p = 0.001), longer t ime required for the porated membrane to reach a certain conductance v alue (p = 0.05), and longer postelectroporation time constant (p = 0.0 05). Furthermore, addition of poloxamer 188 was found to reduce the me mbrane capacitance by similar to 4-8% in 5 min. These findings suggest that poloxamer 188 adsorbs into the lipid bilayers, thereby decreasin g their susceptibility to electroporation.