Subsequently, these experiments were repeated after substituting K+ in the pipette solution with either Na+ or Rb+, whereas K+ in the bath remained unchanged (so-called bi-ionic conditions). Outward currents with kinetics characteristic for NtORK were elicited in the presence of alkali cations other than K+, indicating that the channel was permeable to these cations. However, the current densities obtained with Na+ and Rb+ were significantly lower than those in the presence of K+ (Fig. 1F).