Biomedical subjects

F Beckers

Publications and source records attributed to F Beckers.

20 records · Page 2Linked to original sources

PubMed1979

Reversible electrical breakdown of lipid bilayer membranes: a charge-pulse relaxation study.

Charge-pulse experiments were performed with lipid bilayer membranes from oxidized cholesterol/n-decane at relatively high voltages (several hundred mV). The membranes show an irreversible mechanical rupture if the membrane is charged to voltages on the order of 300 mV. In the case of the mechanical rupture, the voltage across the membrane needs about 50-200 musec to decay completely to zero. At much higher voltages, applied to the membrane by charge pulses of about 500 nsec duration, a decrease of the specific resistance of the membranes by nine orders of magnitude is observed (from 10(8) to 0.1 omega cm2), which is correlated with the reversible electrical breakdown of the lipid bilayer membrane. Due to the high conductance increase (breakdown) of the bilayer it is not possible to charge the membrane to a larger value than the critical potential difference Vc. For 1 M alkali ion chlorides Vc was about 1 V. The temperature dependence of the electrical breakdown voltage Vc is comparable to that being observed with cell membranes. Vc decreases between 2 and 48 degrees C from 1.5 to 0.6 V in the presence of 1 M KCl. Breakdown experiments were also performed with lipid bilayer membrane composed of other lipids. The fast decay of the voltage (current) in the 100-nsec range after application of a charge pulse was very similar in these experiments compared with experiments with membranes made from oxidized cholesterol. However, the membranes made from other lipids show a mechanical breakdown after the electrical breakdown, whereas with one single membrane from oxidized cholesterol more than twenty reproducible breakdown experiments could be repeated without a visible disturbance of the membrane stability. The reversible electrical breakdown of the membrane is discussed in terms of both compression of the membrane (electromechanical model) and ion movement through the membrane induced by high electric field strength (Born energy).

Cell Membrane↗

PubMed1977

The effect of pressure on the electrical breakdown in the membranes of Valonia utricularis.

The interpretation of electrical breakdown in terms of electro-mechanical instabilities, predicts that the breakdown potential should decrease with increasing cell turgor pressure. Experiments were conducted to test this hypothesis on cells of Valonia utricularis over a turgor pressure range of 0.5-10(5)-5.0-10(5) N/m2. Electrical breakdown was measured using intracellular electrodes and 500 mus current pulses. The pressure was monitored by an intracellular micropipette pressure transducer. The results obtained show a linear decrease in the critical breakdown potential with pressure. The effective compressive modulus of the cell membrane, gamma, is calculated from the slope of this line to 69+/-10-10(5) N/m2 (average value of seven measurements). This is consistent with the theoretical prediction of the electromechanical model using our previously determined values of the elastic modulus of the membrane. A theoretical analysis is given of the effects of pressure on the breakdown, This includes also considerations of the indirect effect of pressure on the membrane via stretching of the cell wall with a possible coupling of such strains to the cell membrane. The results and analysis presented allow us to conclude on the basis of the experimentally determined breakdown P.K. of 959 mV that the region of membrane where electrical breakdown occurs is a dielectric with one of the following combinations of parameters: (A) a thickness delta=7-9 nm with a dielectric constant epsilon=greater than 10, e.g. a hydrated protein spanning the whole membrane. (B) delta=4-5 nm with epsilon=3-8, e.g. a lipoprotein of lipid bilayer dimensions. (C) delta approximately 2 nm with epsilon=2-3, e.g. a half lipid bilayer. If we assume that the breakdown P.D. of the tonoplast and plasmalemma are identical, that is 480 mV, then there is only one reasonable choice for the membrane thickness and the dielectric constant: delta=2 nm, epsilon=3-8, e.g. a (lipo) proteinaceous module facing a half life lipid bilayer.

Cell Membrane↗