Figure 4. Effect of transduction protein concentration on physiological properties of rods. A, Representative light-evoked responses from WT rods (C57BL/6J, black), Tr+/− rods (blue), and PDE6AB+/− rods (red). Patch-clamp recordings were made in whole-cell mode [membrane potential (Vm) = −40 mV]. Twenty millisecond light flashes given at time 0 yielded flash strengths ranging from 4 to 550 R*/rod, increasing by a factor of 2. Reduction in expression of transducin or PDE yielded no marked change in response waveforms compared with C57BL/6J rods. B, Intensity–response plot (mean ± SEM) of WT rods (black, n = 10), Tr+/− rods (blue, n = 6), and PDE+/− (red, n = 11). The sensitivity (I1/2) was derived from the best fitting Hill equation, I1/2 = 19.8 ± 1.8, 23.2 ± 3.6, and 20.2 ± 3.2, respectively. Reduction in rod transducin corresponded with a small, albeit nonsignificant, decrease in flash sensitivity (p = 0.47). Reduction in PDE resulted in no significant change in flash sensitivity (p = 0.94). C, Averaged single-photon responses from WT (black), Tr+/− (blue), and PDE+/− (red) rods, time-to-peak 222.5 ± 0.5, 245. ± 19.8, and 232. ± 32.8 ms, respectively. Reduction of neither transducin nor PDE resulted in a significant change in response kinetics.