Figure 3.

Tubulin induces fast flickering of the ionic current through grA channels in a dose- and voltage-dependent manner: (A) grA current traces were obtained at indicated tubulin concentrations in the DPhPC membrane at 200 mV applied voltage. The flickering increases with tubulin concentration and the corresponding decrease of the average conductance (black dotted line indicates conductance at 0 and 3 nM tubulin and red dotted line indicates conductance at 10 and 50 nM tubulin). Current records were filtered with a digital 8-pole Bessel filter at 1 kHz. (B) Power spectral densities of current fluctuations at 50 nM of tubulin (upper trace) can be approximated by a Lorentzian spectrum (smooth line through the data) with a corner frequency of f_c = 600 Hz. (C) Tubulin-induced current fluctuations in the grA channel increase with applied voltage. Power spectral densities of current fluctuations of the single grA channel obtained at applied voltages as indicated in the presence of 50 nM tubulin. Solid lines are fitted with Lorentzian spectra. Current records were filtered with a digital 8-pole Bessel filter at 2 kHz. The medium consisted of 1 M KCl buffered with 5 mM HEPES at pH 7.4.