VOLTAGE-DEPENDENT PORIN-LIKE ION CHANNELS IN THE ARCHAEON HALOFERAX-VOLCANII

Membrane vesicles isolated from the cell envelope of the archaebacteri um Haloferax volcanii were either reconstituted in giant liposomes and examined by the patch-clamp technique or were fused into planar lipid bilayers. In addition, cell envelope proteins were solubilized by det ergent and reconstituted in azolectin liposomes, which were then fused into planar lipid bilayers. Independently of the technique used the p redominant channel activity encountered exhibited the following charac teristics. Channels were open at all voltages in the range approximate ly -120 to +120 mV and exhibited frequent fast transitions to closed l evels of different amplitudes. At voltages greater than 120 mV the cha nnels tended to close in a manner characterized by large, slow transit ions of variable amplitudes. The tendency to close at high membrane po tentials was much stronger at one polarity. The channel gating pattern was complex exhibiting a range of subconductances of 10-300 picosieme ns in symmetric 100 mM KCl. These electrophysiological characteristics are comparable with those of bacterial and mitochondrial porins, sugg esting that the archaeal channels may belong to the general class of p orin channels. Some channels showed preference for K+, whereas the oth ers preferred Cl-, suggesting the existence of at least two types of p orin-like channels in H. volcanii.