BIOPHYSICAL CHARACTERIZATION OF GAP-JUNCTION CHANNELS IN HELA-CELLS

HeLa cells seem not to be junctionally coupled when probed with techni ques such as Lucifer yellow spreading and/or ionic coupling measured w ith three inserted microelectrodes. When investigated with double whol e-cell patch-clamp measurements, HeLa cells in monolayer cultures were electrically coupled in 39% of the cases with very low transjunctiona l conductances (average one to five open channels). These gap-junction channels had a single-channel conductance gamma = 26 +/- 6 pS and wer e voltage-gated with an equivalent gating charge z = 3.1 +/- 1.5 for a voltage of half-maximal inactivation U(o) = 49 +/- 10 mV. The voltage -dependent component represents only 31 +/- 8% of the total junctional conductance. The voltage-insensitive conductance is characterized by a residual open probability p(o)(infinity) = 0.34 +/- 0.12, which corr esponds to a ratio G(min)/G(max) = 0.50 +/- 0.12. Dissociation of mono layer cells into cell pairs yielded about 58% coupled cell pairs with no notably altered single-channel properties.