Figure 2. Voltage-dependent blockage of Na⁺ current by intracellular Rb⁺ and Cs⁺ ions in WT CNGA1 channels.

A, scheme illustrating the nomenclature used for designating intracellular () and extracellular () solutions. X⁺ is the indicated monovalent cation. B, representative WT CNGA1 current recordings from one excised-patch in Na⁺ symmetrical conditions (110 mm /110 mm ) and when intracellular Na⁺ was replaced by an equimolar amount of K⁺, Rb⁺ and Cs⁺, respectively (110 mm /110 mm , 110 mm /110 mm and 110 mm /110 mm ). Currents were elicited in the presence of 1 mm cGMP in the bathing medium and voltage steps ranging from −100 to 40 mV (ΔV = 20 mV). Dashed line indicates 0 current level; arrows indicate the −100 mV Na⁺ current level in symmetrical solution. C, I–V curves in WT CNGA1 channels in the presence of 110 mm intracellular Na⁺ (filled squares), K⁺ (open circles), Rb⁺ (filled triangles) and Cs⁺ (filled circles). D, dependency of residual fractional Na⁺ current I_X/I_Na on voltage when Rb⁺ (filled triangles; n = 5) and Cs⁺ ions (filled circles; n = 6) are in the bathing medium.