Figure 2.
Current responses and sensitivity of juvenile lamprey rod and cone photoreceptors to brief light stimuli. (a) Mean responses of 13 rods to 20 ms 500 nm flashes given at t = 0 at the following intensities (in photons μm−2): 9, 40, 98, 366, 1055 and 2591. (b) Mean responses of six cones to 20 ms 600 nm flashes given at t = 0 at the following intensities (in photons µm−2): 78, 711, 2051, 5036, 1.91 × 104, 2.20 × 105, 6.71 × 105 and 6.96 × 105. (c) Normalized mean current response amplitudes (±s.e.) as a function of flash intensity for rods (closed squares) and cones (open squares). The same cells as in (a) and (b). Data for both cell types were fitted with the Michaelis–Menton equation, r/rmax = I/(I + I½), where r/rmax is the normalized current amplitude, I the flash intensity and I½ the flash intensity producing a half-maximal response. Best-fitting values of I½ were 52 photons μm−2 for rods and 3210 photons μm−2 for cones.