Figure 6.

Pore properties of voltage-insensitive 124Q channels. (A) Unidirectional single channel currents measured at +40 mV (Tris Ringer//“X⁺” EGTA, shaded histograms) and at −40 mV (“X⁺” Ringer//Tris EGTA, open histograms). The histograms show the following permeability sequence: K⁺ > Rb⁺ > NH4⁺ > Cs⁺ and Na⁺. (B) 124Q channels are sensitive to block by 4-AP. I–V data points from one representative oocyte using two-electrode voltage clamp. Macroscopic current seen in 115-mM external K⁺ solution (▴) appears effectively blocked after addition of 10 mM 4-AP to the bath solution (○).