The physiological role of Ca-dependent CNG channel modulation in flash photocurrents. Experimental photocurrents were measured at −40 mV in a dark-adapted bass single cone in response to 10-msec flashes of intensities: 71, 167, 710, and 3,561 VP*. The panels on the left illustrate experimental (gray traces, noisy) and simulated (black traces, noiseless) photocurrents computed with the normal complete model (Table 3, Cone 1). The panels on the right reproduce the same experimental data (gray traces, noisy), now superimposed by simulated photocurrents (black traces, noiseless) computed with a model in which CNG channel modulation is omitted.