Fig. 2.

Modulation of ion current through a single PA₆₃ channel by AmPrβCD. Using higher salt concentrations (1 M KCl, pH 6.6), we are able to resolve discrete reversible interruptions in the ion current through a single channel. In the absence of cyclodextrin the ion movement is mainly determined by the geometry and the surface properties of the pore (topmost track). Fast flickering between open and closed states inherent to PA₆₃ channels [so-called voltage gating (12, 25)] was mainly removed by averaging over a time interval of 50 msec. In the presence of 13 nM AmPrβCD in the cis half of the chamber, the channel gets spontaneously blocked, and at higher AmPrβCD concentrations (80 nM and 1.8 μM) channel blockages are more frequent.