Computerized analysis of ionic channel multi-state conductance in planar lipid bilayers

Ionic transport through cell membranes controls many physiological processes in living organisms. Transport across the cell surface is mediated by membrane proteins (channels), which form hydrophilic pathways permeable to various ions. Also, many synthetic peptides and bacterial toxins form ionic channels when incorporated in lipid bilayer membranes. Changes in boundary physico-chemical conditions and modifications of protein conformation, or sequence, give rise to ionic current signals with different characteristics. A low-cost MS-DOS-based system interfaced to a 12 bit analog/digital/analog (A/D/A) board was used for data acquisition and analysis of square-shaped signals due to the open-closed transitions of single-channel molecules. A dedicated software was developed to investigate the conductance of channels that generate bursts of current, i.e. a sequence of current events due to the rapid flickering of the protein between the open and closed configurations. Up to three current levels present within the same burst can be identified from the best fit of current histogram distribution with the sum of three gaussians. Results obtained from the incorporation of a tetanus toxin channel into phosphatidylserine planar bilayers are reported.