[Kinetic parameters of single ion channels and stationary conductivities of phytotoxin modified lipid bilayers]

As shown earlier, phytotoxins produced by Pseudomonas syringae pv. syringae form ion channels of "small" and "large" conductance when incorporated into planar lipid membranes. The multilevel conductance is due to cluster organization of the channels (Kaulin et al., 1998; Gurnev et al., 2002). In this study the kinetic parameters of syringomycin E (SRE) and syringostatin A (SSA) channels in negatively charged bilayer lipid membranes were estimated. The average time of open state of the small channels (t(s)(open)) did not depend on transmembrane voltage (in the range of +/- 200 mV). The channel characteristics differed between two phytotoxins: the t(s)(open) for the SRE-channels was much larger than that for SSA-channels. An energetic diagram with two non-conducting states illustrating the formation of the small channel is proposed to explain the voltage independence of the kinetic parameters. The probability for synchronous functioning of small channels with SSA was higher than that with SRE. To analyse the role of the clusters in the biological activities of SRE and SSA, we estimated the cluster contribution to a net transmembrane currents to be 60 and 90%, respectively.