Voltage-Induced Nonconductive Pre-Pores and Metastable Single Pores in Unmodified Planar Lipid Bilayer

Abstract

Electric fields promote pore formation in both biological and model membranes. We clamped unmodified planar bilayers at 150-550 mV to monitor transient single pores for a long period of time. We observed fast transitions between different conductance levels reflecting opening and closing of metastable lipid pores. Although mean lifetime of the pores was 3 +/- 0.8 ms (250 mV), some pores remained open for up to approximately 1 s. The mean amplitude of conductance fluctuations (approximately 500 pS) was independent of voltage and close for bilayers of different area (40,000 and 10 microm(2)), indicating the local nature of the conductive defects. The distribution of pore conductance was rather broad (dispersion of approximately 250 pS). Based on the conductance value and its dependence of the ion size, the radius of the average pore was estimated as approximately 1 nm. Short bursts of conductance spikes (opening and closing of pores) were often separated by periods of background conductance. Within the same burst the conductance between spikes was indistinguishable from the background. The mean time interval between spikes in the burst was much smaller than that between adjacent bursts. These data indicate that opening and closing of lipidic pores proceed through some electrically invisible (silent) pre-pores. Similar pre-pore defects and metastable conductive pores might be involved in remodeling of cell membranes in different biologically relevant processes.

Imaging the dynamics of individual electropores

“…Increasing the applied potential difference is predicted to lower and broaden the local energy minimum that supports the hydrophilic pore, and lower the barrier to unbounded pore expansion. electrical recording (5,22,23); however, here, by isolating individual oSCR signals, we are able to extend observation of these phenomena to higher potentials, where the individual signals would be obscured in a purely electrical measurement. We have observed that all of these modes can occur at elevated potentials, with no apparent favor of one mode over another.…”

“…The transient nature and small size of electropores place significant limitations on the measurement of electropore dynamics, and more fundamentally on their direct detection. Electrical single-channel recording (SCR) can resolve these dynamics at high time resolution (22,23); however, SCR is limited in that it can only detect the total current across the membrane, and is thus unable to resolve whether conductance events are due to single or multiple permeabilization events. Indeed, the most common characteristic for electroporation in SCR would be a "noisy" trace that precedes bilayer rupture (see Fig.…”

Bax-type Apoptotic Proteins Porate Pure Lipid Bilayers through a Mechanism Sensitive to Intrinsic Monolayer Curvature

“…Since there are no constant, unitary conductance steps in these recordings, they do not resemble recordings from typical ionic channels where the conduit from one side of the membrane to the other is exclusively lined by protein. Instead, these results reveal striking similarities to lipidic pores, in which the pore is lined by lipid headgroups (9,10).…”

Shape bistability of a membrane neck: A toggle switch to control vesicle content release

“…Membrane tubules were made by patch-clamping a planar phospholipid bilayer membrane formed on a Teflon orifice (30). A fire-polished glass pipette was pressed against the planar BLM Abbreviations: BLM, bilayer lipid membrane; DPhPC, diphytanoyl phosphatidylcholine; DNPC, dinervonoyl phosphatidylcholine; OPC, oleoyl phosphatidylcholine; OPE, oleoyl phosphatidylethanolamine; Chol, cholesterol; cP, centipoise; NT, narrow tubule; WT, wide tubule.…”