Study of conductance changes of bilayer lipid membrane induced by electric field

Changes in the bilayer lipid membrane (BLM) conductance induced by electric field were studied. BLMs were formed from diphytanoylphosphocholine (DPhPC) solution in squalene. Certain time after a constant voltage (200-500 mV) was applied to the BLM in the voltage-clamp mode, the BLM conductance started to grow UP to similar to 10 nS until the BLM ruptured. The conductance often changed abruptly (with the front duration of less than 33 mu s) and then stabilized for a relatively long Lime (up to 10 s; 300 ms in average) thus resembling the ion channel activity. The mean amplitude of conductance steps was 650 pS, However, in some cases a slow conductance drift was recorded, When N-methyl-D-glucamineiglutamate ions were used instead of KCI, the conductance changes became 5 times smaller, We suggest that formation in the BLM of single pores similar to 1 nm in diameter should result in the observed changes in the BLM conductance. The BLM conductance growth was due to consecutive opening of several such pores. When the electric field amplitude was abruptly decreased (down to 50-100 mV), the conductance dropped rapidly to the background value. When we increased the voltage again, the BLM conductance right after the increase depended on the time BLM spent under "weak" electric field, If this time exceeded 500 ms, the conductance was at the background level, but when the time was diminished, the conductance reached the value recorded before the voltage decrease, These data imply that closure of the pores should lead to the formation in BLM of small defects (prepores) that can be easily transformed into pores when the voltage is increased. The lifetime of such prepores did not exceeded 500 ms.