Electrical Properties of Phospholipid Vesicles

Abstract

The capacitance of the membrane of phospholipid vesicles and the electrical properties of the vesicle interior have been determined. To this end the electrical properties of phospholipid vesicles have been investigated over a frequency range extending from 1 kHz to 100 MHz. The dielectric behavior is characterized by two dispersions, one placed between 1 kHz and 1 MHz and the other between 1 and 100 MHz. The relaxational behavior at low frequencies is explained by counterion movement tangential to the vesicle surface and a reasonable value for the fixed charge of the vesicles is calculated from the dispersion magnitude. The relaxation at high frequencies is of the Maxwell-Wagner type and appears caused by the phospholipid bilayer bounding the interior phase of the vesicles. It is consistent with the existence of a closed bilayer with a capacitance of about 2 muF/cm(2) and an internal phase similar to the vesicle suspending medium. There is no indication of other than normally structured water inside the small vesicles.

The radio-frequency dielectric properties of yeast cells measured with a rapid, automated, frequency-domain dielectric spectrometer

“…1, 11, 49, 61), based upon the assumption that the cell membrane is essentially non-conducting at low frequencies, is where r is the cell radius (neglecting the cell wall) and C, the specific capacitance of the cell membrane (per cm2). Equation (6) permits the physically unreasonable assumption that the membrane volume is a negligible fraction of the total volume (and also that cells do not shield each other), and Schwan et al [58] therefore extended equation (6) as follows:…”

“…This is because such a dielectric increment depends strongly on both the volume fraction and the radius of the suspended particles, and the diameter of the phospholipid vesicles used was very small [13.5 nm]; indeed, the accessible volume fractions used in the above study (Ref. 58, cf. also Ref.…”

On-Line, Real-Time Measurements of Cellular Biomass using Dielectric Spectroscopy

“…Figure 4 is (Schwan and Morowitz, 1962;Schwan et al, 1970;Harris and Kell, 1983;Davey et al, 1992). Schwan (1957) also gives an equation for the characteristic (critical) frequency (f c ) of 2.0x10 6 Hz (2.0MHz) (For useful values to use in calculations such as these see .…”

Dielectric spectroscopy of single cells: time domain analysis using Maxwell's mixture equation

“…Measurements provide information about the structure, function and electrical characteristics of the system. The early work of Maxwell [1] and Wagner [2], Fricke [3][4][5], Cole [6][7][8] and Schwan [9][10][11][12], amongst others, laid the foundations for this field of research; see [13] for a review. The frequency dependent dielectric properties of a mixture of membrane-bound particles are characterized by a pronounced dielectric relaxation in the 1-100 MHz range which is due to interfacial charging, and was termed the β-relaxation (for cells) by Schwan [10].…”