Figure 6.
Dim-flash responses of Gnb3−/− cones have reduced sensitivity and amplification whereas response kinetics are similar to those of WT. Responses to the dimmest flashes from the response families like those shown on Figure 5A were divided by the corresponding flash intensity to calculate responses to 1 photon per μm2 for sensitivity and amplification analysis (left column), or scaled to the unity amplitude for the kinetic analysis (right column). The first three rows plot dim flash responses recorded from cones of a particular genotype as indicated on the figure. The individual responses are shown with thin gray traces, “n” indicates the number of cone records for each genotype. Population averaged responses are shown with thickened black traces. The dashed gray traces in A and E show responses from two slow WT cones that were excluded from the population average. A–C, Normalized responses per photon. D, Population averaged “single-photon” responses for the three different genotypes. Activation theory traces (thin black traces) calculated for a flash with intensity of 1 photon per μm2 were fitted to the population averaged responses and the values of the amplification constant are shown on the graph. The peak amplitudes are indicated with thin dashed lines. E–G, Dim-flash responses scaled to unity amplitude. The thickened dark gray trace in E that overlaps with black trace shows the M-dominant cone population-averaged response from Nikonov et al., 2006. The trace was shifted to the left by 14 ms to account for the difference in the hardware related delays in the current and previous studies (11 and 25 ms correspondingly). The inserts illustrate analysis of the tail phases of the population-averaged dim-flash responses. Averaged responses replotted from the corresponding panels (left ordinates, linear scales) and response tail phases (right ordinates, logarithmic scales) are shown on the same time axis with light gray traces. The slopes of the lines fitted to the response tail phases in the semilogarithmic coordinates give values of the τtail time constant, same τtail values were used to generate exponential traces for fitting response tail phases in the linear coordinates. H, The normalized population averaged responses for the three different genotypes demonstrate the similar shape of the response.