Limits...
Metastable pores at the onset of constant-current electroporation.

Kotulska M, Basalyga J, Derylo MB, Sadowski P - J. Membr. Biol. (2010)

Bottom Line: During this stage two species of metastable pores open, the majority of very low conductance that seem not fully developed as hydrophilic electropores.Membrane capacitance has a great impact on the membrane susceptibility to the pore appearance, related to its thickness and integrity.Pores of nonperfect membranes appear more easily, but they do not live any longer than others.

View Article: PubMed Central - PubMed

Affiliation: Institute of Biomedical Engineering and Instrumentation, Wroclaw University of Technology, ul. Wybrzeze Wyspianskiego 27, 50-370, Wroclaw, Poland. malgorzata.kotulska@pwr.wroc.pl

ABSTRACT
Single metastable nanopores, appearing before the actual electroporation under constant-current conditions, are used to characterize the onset of electroporation. Unlike the long-lived electropores typical of the current controlled methods, these pores survive for milliseconds and observing them is possible due to slow development of electroporation, provided by the gradual accumulation of charges on a planar membrane. Analysis of the metastable pore appearance frequency and lifetime shows the first introductory stage of electroporation. During this stage two species of metastable pores open, the majority of very low conductance that seem not fully developed as hydrophilic electropores. The experiments reveal that voltage value defines the electroporation onset while the current value affects the rate of electroporation. Membrane capacitance has a great impact on the membrane susceptibility to the pore appearance, related to its thickness and integrity. Pores of nonperfect membranes appear more easily, but they do not live any longer than others.

Show MeSH
Metastable pores may not be fully formed, exposing their hydrophobic parts to contact with microleaks of ions and water. Hypothetical metastable pore
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2914259&req=5

Fig3: Metastable pores may not be fully formed, exposing their hydrophobic parts to contact with microleaks of ions and water. Hypothetical metastable pore

Mentions: The appearance of such prepores indicates limiting conditions of the actual electroporation and membrane susceptibility to the electric field, which relates to the membrane structure and mechanical properties. Our hypothesis is that metastable pores are not fully formed, exposing their hydrophobic parts to contact with microleaks of ions and water, as schematically depicted in Fig. 3. These pores tend to close when the voltage is not well above the electroporation threshold. Molecular dynamics simulations show that pore formation starts with water “wires” that invade the membrane, subsequently triggering reorganization of the lipid molecules and final formation of hydrophilic pores if the leak continues (Tieleman 2004; Tarek 2005). The hydrophilic pore, fully formed, will not reseal immediately, and even closed will keep structural changes in the membrane for some time (Melikov et al. 2001). Resealing in the prepore experiment, presented here, should be even more difficult since the voltage is constantly rising and charge is accumulating on the membrane. The fact that metastable pores manage to close completely in such adverse conditions suggests that lipids have not fully reoriented themselves and that the pore is surrounded by abundant lipid molecules. The pores we present here could be regarded as opposite to the prepores observed by Melikov et al. (2001). In that experiment, conducted in the voltage-clamp mode, the silent and nonconductive prepores were observed at a voltage below the electroporation threshold following pulses that ensure electroporation. These prepores do not conduct ions, but they keep reoriented lipid molecules that remember the previously open hydrophilic pore. In our case the situation is reversed. The metastable pores, which also typically appear at a voltage below the electroporation threshold and can be regarded as prepores, conduct ions but the lipid molecules have not adjusted to this situation and maintain their nonreoriented position.Fig. 3


Metastable pores at the onset of constant-current electroporation.

Kotulska M, Basalyga J, Derylo MB, Sadowski P - J. Membr. Biol. (2010)

Metastable pores may not be fully formed, exposing their hydrophobic parts to contact with microleaks of ions and water. Hypothetical metastable pore
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2914259&req=5

Fig3: Metastable pores may not be fully formed, exposing their hydrophobic parts to contact with microleaks of ions and water. Hypothetical metastable pore
Mentions: The appearance of such prepores indicates limiting conditions of the actual electroporation and membrane susceptibility to the electric field, which relates to the membrane structure and mechanical properties. Our hypothesis is that metastable pores are not fully formed, exposing their hydrophobic parts to contact with microleaks of ions and water, as schematically depicted in Fig. 3. These pores tend to close when the voltage is not well above the electroporation threshold. Molecular dynamics simulations show that pore formation starts with water “wires” that invade the membrane, subsequently triggering reorganization of the lipid molecules and final formation of hydrophilic pores if the leak continues (Tieleman 2004; Tarek 2005). The hydrophilic pore, fully formed, will not reseal immediately, and even closed will keep structural changes in the membrane for some time (Melikov et al. 2001). Resealing in the prepore experiment, presented here, should be even more difficult since the voltage is constantly rising and charge is accumulating on the membrane. The fact that metastable pores manage to close completely in such adverse conditions suggests that lipids have not fully reoriented themselves and that the pore is surrounded by abundant lipid molecules. The pores we present here could be regarded as opposite to the prepores observed by Melikov et al. (2001). In that experiment, conducted in the voltage-clamp mode, the silent and nonconductive prepores were observed at a voltage below the electroporation threshold following pulses that ensure electroporation. These prepores do not conduct ions, but they keep reoriented lipid molecules that remember the previously open hydrophilic pore. In our case the situation is reversed. The metastable pores, which also typically appear at a voltage below the electroporation threshold and can be regarded as prepores, conduct ions but the lipid molecules have not adjusted to this situation and maintain their nonreoriented position.Fig. 3

Bottom Line: During this stage two species of metastable pores open, the majority of very low conductance that seem not fully developed as hydrophilic electropores.Membrane capacitance has a great impact on the membrane susceptibility to the pore appearance, related to its thickness and integrity.Pores of nonperfect membranes appear more easily, but they do not live any longer than others.

View Article: PubMed Central - PubMed

Affiliation: Institute of Biomedical Engineering and Instrumentation, Wroclaw University of Technology, ul. Wybrzeze Wyspianskiego 27, 50-370, Wroclaw, Poland. malgorzata.kotulska@pwr.wroc.pl

ABSTRACT
Single metastable nanopores, appearing before the actual electroporation under constant-current conditions, are used to characterize the onset of electroporation. Unlike the long-lived electropores typical of the current controlled methods, these pores survive for milliseconds and observing them is possible due to slow development of electroporation, provided by the gradual accumulation of charges on a planar membrane. Analysis of the metastable pore appearance frequency and lifetime shows the first introductory stage of electroporation. During this stage two species of metastable pores open, the majority of very low conductance that seem not fully developed as hydrophilic electropores. The experiments reveal that voltage value defines the electroporation onset while the current value affects the rate of electroporation. Membrane capacitance has a great impact on the membrane susceptibility to the pore appearance, related to its thickness and integrity. Pores of nonperfect membranes appear more easily, but they do not live any longer than others.

Show MeSH