18-beta-Glycyrrhetinic Acid (BGA) as an electrical uncoupler for intracellular recordings in confluent monolayer cultures

In the study of epithelial cell biology, primary cell cultures or cell line s grown to confluency offer considerable advantages compared with isolated cells and cell clusters. This is due mainly to the development of appropria te cell-to-cell contacts that are a prerequisite for cell polarity and thus vectorial solute transport. On the other hand, electrical coupling via gap junctions in most instances significantly hinders the use of voltage-clamp techniques for electrophysiological analysis of transport processes in sin gle cells. In the present study we employed the gap junctional blocker 18-b eta -glycyrrhetinic acid (BGA) to reduce electrical cell-to-cell coupling i n confluent primary cultures of rat hepatocytes. In current-clamp experimen ts, 40 mu mol/l BGA reversibly increased apparent cell input resistance app roximately tenfold. Due to this partial electrical isolation of cells, two- channel voltage-clamp experiments became feasible and, for the first time, the hypertonicity-induced Na+ conductance of rat hepatocytes could be analy sed quantitatively. In ion substitution experiments, however, it became obv ious that BGA, while leaving Na+ and K+ conductances virtually unchanged, c ompletely blocked cell membrane Cl-conductance. This additional effect of B GA necessitates independent control experiments to ensure that the transpor t process under consideration is itself not changed by the compound. Nevert heless, BGA may serve as a powerful tool for the quantitative electrophysio logical study of epithelial cells that are in quasi physiological contact w ith their neighbours.