Biophysical characterization of gap-junction channels in HeLa cells

HeLa cells seem not to be junctionally coupled when probed with techniques such as Lucifer yellow spreading and/or ionic coupling measured with three inserted microelectrodes. When investigated with double whole-cell patch-clamp measurements, HeLa cells in monolayer cultures were electrically coupled in 39% of the cases with very low transjunctional conductances (average one to five open channels). These gap-junction channels had a single-channel conductance gamma = 26 +/- 6 pS and were voltage-gated with an equivalent gating charge z = 3.1 +/- 1.5 for a voltage of half-maximal inactivation Uo = 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 po (infinity) = 0.34 +/- 0.12, which corresponds to a ratio Gmin/Gmax = 0.50 +/- 0.12. Dissociation of monolayer cells into cell pairs yielded about 58% coupled cell pairs with no notably altered single-channel properties.