The external K ⁺ sensitivity of alanine mutants of the pore region (amino acids I268–V355). Typical current traces of alanine mutants measured at 0.2 mM (red and 100 mM (black) external K⁺. Currents were elicited by depolarization of membrane from holding potential −100 to +60 mV. Recordings were started at 0.2 mM K⁺_o. After stabilization of the amplitudes, the 100 mM K⁺ containing solution was applied. Red traces correspond to the last recording point in 0.2 mM K⁺, black traces correspond to the first point in 100 mM K⁺.