Photocurrents measured under voltage clamp at −40 mV in a dark-adapted bass single cone in response to 10-msec flashes or 2-s steps of 540-nm light. (A) Responses elicited with flashes of intensities: 9, 18, 37, 91, 178, 372, 913, 1,933, 3,685, and 9,133 VP*. Peak amplitude increases with light intensity (right) in a manner well described by an exponential saturation function (Eq. 1.1; continuous line), with Ipeak = 18.8 pA and k = 260.1 VP*. The inset is a log–log plot to show that signal threshold was ∼8 VP*. (B) Responses elicited with step stimuli of intensities: 65, 327, 651, 1,635, 3,266, 6,513, 16,369, 65,131, and 163,687 VP*/s. The current at its peak (•) is more sensitive to light than in the stationary state (▽; right). Amplitude dependence on light intensity is well described by a Michaelis–Menten function (Eq. 1.2; continuous line), with Ipeak = 21.8 pA and σ = 1,844 VP*/s for the response at its peak, and Imax = 21.8 pA and σ = 3,522 VP*/s for the response at 2 s. The inset is a log–log plot of the peak amplitude of the step response to show that signal threshold was 56 VP*/s.