Figure 1. Single CNGA1 channel currents at saturating cGMP (700 μm) with either symmetrical Na⁺ or K⁺ ions at +100 mV.

A, current traces. K⁺ ions produced openings smaller in amplitude, longer in duration, and with a less noisy open level compared to Na⁺ ions. B, amplitude histograms. All-point histograms were fitted with the sum of two Gaussian functions yielding the indicated values for the mean (i_o1, i_c) and standard deviation (σ_o1, σ_c) at the open and closed levels, respectively. σ_n1 indicates the extra RMS noise of the open channel calculated using eqn (7). C, cumulative open-time histograms. The histograms were fitted with eqn (1b) yielding the indicated parameters. Both open time constants are shorter for Na⁺ than for K⁺ currents.