Show description

When a cell, which may be considered as a hollow thin-walled sphere, is exposed to such an electric field, a voltage will be imposed across its membrane. The magnitude of this potential depends on the intensity of the field [E (V/cm)] and the size of the cell [radius r (cm)] and will vary around the cell's circumference. With reference to Fig. I the voltage at point P (Vp) across the membrane of a spherical cell is given by the simplified equation Vp = C" r" E " cos 0 volts where the value of the constant C depends on the relative conductivities of the extracellular fluid, the cytosol, and the membrane.

W 3-J 2- Z rim 1 - j J J c ~ J f t d J u3 0 0 I 2 I 5 FIELD I 10 STRENGTH (KV I 15 CM -1) FIG. 2. The expected membranepotential [from Eq. 2 #m diameteras a resultof exposureto variousfield strengths. Methodology Two methods have been used routinely to subject isolated cells to electric fields: (a) passing cells through a Coulter counter 2 and (b) discharging a capacitor through a cell suspension. The main disadvantage of using the Coulter-counter method is the length of time taken to harvest a worthwhile number of "leaky" cells, and for this reason we routinely use the second method, which is described below.

Temperature 37*. (c) Effect of Mg acetate on Ca-sensitive release of catecholamine. Cells on a K glutamate solution (Table I) were rendered "leaky" by 10 exposures of 2 kV cm -t (~ = 200 #sec) and immediately transferred to similar solutions containing various concentrations of free Mg 2+ (Mg acetate used). After 5-min incubation the cells were challenged with 10 m M Ca EGTA buffer and the catecholamine was determined 10 rain later. Temperature 37*. (d) Ca activation curves at different chloride concentrations.