Functional comparison of bovine CNGA1 and P366T mutant. (A; left) Sample traces of single-channel recordings of bovine CNGA1 and P366T at −100 mV in cell-attached configuration. (Right) Histogram of single-channel current at −100 mV. (B) Normalized macroscopic currents of wild-type bovine CNGA1 and P366T mutant as a function of [cGMP]_i measured in inside-out patches at −100 mV. Data are fitted to the Hill equation. The K_1/2 and n of bovine CNGA1 are 39.5 ± 3.6 µM and 1.2, respectively. The K_1/2 and n of P366T are 41.2 ± 4.7 µM and 1.3, respectively. (C) I-V curves of bovine CNGA1 and P366T mutant measured from outside-out patches at different external (bath) Ca²⁺ concentrations. (D) Fraction of unblocked current (I/I_max) at −100 mV as a function of Ca²⁺ concentration. Data are fitted into a Hill equation, with K_i of 3.5 ± 0.5 µM and n of 1.03 for bovine CNGA1 and K_i of 6.0 ± 0.7 µM and n of 1.36 for P366T. All error bars are mean ± SEM from five measurements.