Surface contact measurement of electrical cell uncoupling in the mouse heart during ischemia

Electrical cell uncoupling via gap junction closure is assumed to cause characteristic changes of the passive dielectric spectrum of ischemic heart tissue. In order to find an independent evidence for this assumption, we analysed heart tissue during ischemia, measured the open state of gap junctions by means of dye transfer and correlated this parameter with the time course of the dielectric permittivity. The hearts were pre-ischemically arrested by perfusion with Ringer solution containing 20 mmol/L of potassium (group KCL, n=10). This solution was also used with the addition of two gap junction blockers, either 3 mmol/L heptanol (group HEP, n=4) or 20 micromol/L palmitoleic acid (group PA, n=7). During subsequent ischemia at 21.0+/-0.5 degrees C, we monitored the passive dielectric permittivity spectrum and the spread of dye. After a sigmoidal increase the dielectric permittivity reached an upper plateau at 61+/-22 min of ischemia in KCL, at 45+/-7 min in PA, and already during perfusion at 2+/-1 min in group HEP. At the beginning of ischemia, dye migrated to neighbouring cells in groups KCL and PA but not in HEP. In KCL and PA, the intercellular diffusion of dye stopped after 64+/-26 and 40+/-11 min of ischemia, respectively. Our results suggest that the sigmoidal increase in dielectric permittivity and the reduction of dye diffusion depend on a common mechanism, namely gap junction closure.