Studies of cell pellets: I. Electrical properties and porosity

Abstract

Cell pellets formed by centrifugation provided a good system to study the osmotic behavior, electroporation, and interaction between cells. Rabbit erythrocyte pellets were used in this study because they were simpler than nucleated cells to model analytically. Structurally, cell pellets possessed properties of porous solid bodies and gels. Electrically, cell pellets were shown to behave as a parallel set of resistance, Rp, and capacitance, Cp. Information on pellet structures was obtained from electric measurements. The pellet resistance reflected the intercellular conductivity (porosity and gap conductivity), whereas the pellet capacitance depended mostly on membrane capacitance. The pellet resistance was more sensitive to experimental conditions. The intercellular gap distance can be derived from pellet porosity measurements, providing the cell volume and surface area were known. Rp increased and relaxed exponentially with time when centrifugation started and stopped; the cycles were reversible. When supernatants were exchanged with solutions containing hypotonic electrolytes or macromolecules (such as PEG) after the pellets were formed, complicated responses to different colloidal osmotic effects were observed. A transient decrease followed by a large increase of Rp was observed after the application of a porating electric pulse, as expected from a momentary membrane breakdown, followed by a limited colloidal-osmotic swelling of pelleted cells. The equilibrium values of Rp, Cp, pellet porosity, and intercellular distances were measured and calculated as functions of cell number, centrifugation force, and ionic strength of the exchanged supernatant. Thus, the structure and properties of cell pellets can be completely characterized by electrical measurements.

Tension‐voltage relationship in membrane fusion and its implication in exocytosis

“…3). The tension on the membrane was determined by the centrifugation speed [21] but an increase of the centrifuge acceleration did not increase the fusion yield. Increase in membrane tension after pulsation had no effect on fusion.…”

Improving electrotransfection efficiency by post-pulse centrifugation

“…It is known that postpulse pelleting can decrease the electrolysis of pulsed erythrocytes due to the inhibition of colloidal osmotic swelling. 10,15 The thicker the post-pulse pellet, the lower the electrolysis. However, the thick pellet also poses a hindrance to the supply of nutrients.…”

“…3,10 There are several ways to reduce post-pulse cell swelling. 10,17 Forming a pellet immediately after pulse would reduce erythrocyte swelling, 10,15 and therefore give more time for cells to reseal and reduce cell lysis. In this study, we set to test if what we learned from erythrocytes 10 and hybrid cells 3 can be applied to …”

“…10,15 This feature may be used to reduce postpulse cell mortality in cultured cells. Furthermore, postpulse pelleting does not interfere with the pulsing procedure.…”

In vivo electrical impedance measurements during and after electroporation of rat liver

“…Passive electrical properties of the tissue are measured during and after the application of the electroporation pulse thanks to an automated switching scheme (this strategy has been employed previously by some researchers in the field [19,20]). After the electroporation pulse the impedance of the tissue between the electrodes is measured by using the four-electrode method in which the electroporation electrodes are used as the current injection electrodes and a pair of smaller inner electrodes are used to measure the induced voltage difference across the tissue sample.…”