Vagaries of artificial bilayers and gating modes of the SCl channel from the sarcoplasmic reticulum of skeletal muscle

The elucidation of the structure-function relation of reconstituted ion channel proteins into artificial planar bilayers is expected to be greatly influenced by the physical properties of these bilayers. The dependence of the gating mode of a voltage- and calcium-dependent small chloride channel (SCI channel) on the bilayer properties, as deduced from the specific bilayer capacitance, C-b, was investigated. In bilayers having a C-b value of 0.42 mu F/cm(2) the SCl channel was in the ''burst mode''. At a C-b value of 0.28 mu F/cm(2) the ''burst mode'' gave way to a ''flickering mode''. At C-b values between 0.24 and 0.28 mu F/cm(2) channel bursts were often infrequent and brief. No ion channel activities were observed at C-b values lower than 0.24 mu F/cm(2). These results suggest that changes in bilayer thickness, mediated via n-decane, contribute to changes in channel gating mode, i.e. ''gear shift''. Standardizing C-b and its time-independence are important in comparative and detailed investigations of ion channel characteristics.