Figure 8.

Effect of the 12′ δS→T mutation on diliganded activity. Display f_c ≅ 6 kHz. In addition to inward currents (approximately −100 mV), outward currents (approximately +50 mV) were also recorded in the presence of 2 mM ACh or 2 mM acetylthiocholine to relieve fast blockade by the agonist itself. This was not necessary in the presence of 20 mM choline because the increase in open-channel noise due to fast blockade was much lower (Grosman and Auerbach 2000). Openings are downward deflections at −100 mV and upward deflections at +50 mV. The higher amplitude of the δS→T currents in the presence of 2 mM ACh at +50 mV, as compared with that of the wild type, is most likely due to the slower closing rate constant of the mutant.