Amphotericin B channels in phospholipid membrane-coated nanoporous silicon surfaces: implications for photovoltaic driving of ions across membranes.

The antimycotic agent amphotericin B (AmB) functions by forming complexes with sterols to form ion channels that cause membrane leakage. When AmB and cholesterol mixed at 2:1 ratio were incorporated into phospholipid bilayer membranes formed on the tip of patch pipettes, ion channel current fluctuations with characteristic open and closed states were observed. These channels were also functional in phospholipid membranes formed on nanoporous silicon surfaces. Electrophysiological studies of AmB-cholesterol mixtures that were incorporated into phospholipid membranes formed on the surface of nanoporous (6.5 nm pore diameter) silicon plates revealed large conductance ion channels ( approximately 300 pS) with distinct open and closed states. Currents through the AmB-cholesterol channels on nanoporous silicon surfaces can be driven by voltage applied via conventional electrical circuits or by photovoltaic electrical potential entirely generated when the nanoporous silicon surface is illuminated with a narrow laser beam. Electrical recordings made during laser illumination of AmB-cholesterol containing membrane-coated nanoporous silicon surfaces revealed very large conductance ion channels with distinct open and closed states. Our findings indicate that nanoporous silicon surfaces can serve as mediums for ion-channel-based biosensors. The photovoltaic properties of nanoporous silicon surfaces show great promise for making such biosensors addressable via optical technologies.

Large-conductance cholesterol-amphotericin B channels in reconstituted lipid bilayers.

The antimycotic activity of amphotericin B (AmB) depends on its ability to make complexes sterols to form ion channels that cause membrane leakage. To study this phenomenon, surface pressure (pi) as a function of surface area (A) and pi-A hysteresis were measured in monolayers of AmB-cholesterol mixtures on the water-air interface. The most stable monolayers were produced from molecules of AmB and cholesterol with 2:1 stoichiometry. At this ratio, AmB and cholesterol interact to form ion channels in lipid bilayers with millisecond dwell times and conductances of 4-400 pS. The AmB-cholesterol complexes assemble in three, four, etc., subunit aggregates to form ion channels of diverse and large-conductances. Their I-V characteristics were linear over a range of +/-200 mV. The channel currents were inhibited by the addition of tetraethylammonium (TEA), potassium channel blocker, to the cis-side of the membrane. Likewise, AmB-cholesterol complexes reconstituted in membrane-coated nanoporous silicon dioxide surfaces showed single channel behavior with large amplitudes at various voltages. Large-conductance ion channels show great promise for use in biosensors on solid supports.