The effect of lanthanum on alamethicin channels in black lipid bilayers

The properties of alamethicin channels in dioleyl phosphatidylcholine bilayers were studied in 1 M LaCl3 and were compared with those in 1 M NaCl. Single-channel recordings demonstrated that the mean single-channel life-time is about 0.25 s in NaCl but only about 17 ms in LaCl3. Whereas in NaCl the conductance levels 2 and 3 are mostly populated, in LaCl3 the levels 0 and 1 are preferentially adopted. The single-level conductance are slightly smaller in LaCl3 if the higher bulk solution conductivity of LaCl3 is taken into account. Multipore experiments confirmed earlier results (Boheim, G., Irmscher, G. and Jung, G. (1978) Biochim. Biophys. Acta 507, 485--506) that the bilayer conductance is less strongly dependent on voltage in LaCl3 than in NaCl solution. Current-fluctuation analysis showed that this effect can be explained by a less strong dependence on voltage of the pore-formation rate as well as of the mean channel life-time in LaCl3. The data can be interpreted as an increased lateral diffusion mobility of the alamethicin monomers in the bilayer. This can be the result of the binding of La3+ to the polar headgroups which can induce cluster formation of the phospholipids.