The influence of surface charges on the conductance of the human connexin37 gap junction channel

The single-channel conductance of the hCx37 homotypic gap junction channel does not saturate with transjunctional voltages up to +/-75 mV, nor does it depend linearly on the intracellular electrolyte concentration. The averag e maximum unitary conductances measured in KCI were 175 pS (30 mM), 236 pS (55 mM), 343 pS (110 mM), and 588 pS (270 mM) in the presence of 0.1 mM MgC l2, The unexpectedly high unitary conductance at low salt concentrations ca n be explained by fixed charge groups within or near the channel orifice. F ixed cytoplasmic surface charges (3.4 e) positioned adjacent (15 Angstrom) to the channel pore adequately model the data (surface charge density of 0. 24 e/(nm)(2)). In other experiments, high Mg2+ reduced the unitary conducta nce of hCx37 homotypic gap junction channels more than predicted by screeni ng alone, consistent with specific effects of Mg2+ on the channel.