Figure 5.
Examples of flash response families and response analysis in cones. The first three rows present data recorded from a single cone of a particular genotype as indicated on the figure. A, Families of responses to a series of 5 ms 500 nm flashes of graded intensities. At least 60 individual responses were averaged for the dimmer flashes and at least 15 individual responses were averaged for the brighter flashes. The gray horizontal lines indicate estimated levels of the maximum (saturating) response amplitude corresponding to a complete closure of the light sensitive channels. The “nose” component above the gray lines was not light sensitive and was excluded from further analysis by the response normalization (see Materials and Methods). For each cell, responses were normalized to the saturating response amplitude (average of 6 pA for WT and Gnb3+/− and 8 pA for Gnb3−/− cones). B, Responses to the dimmer flashes from the response families of column A were plotted on a faster time scale together with the Lamb and Pugh activation theory traces (thickened gray traces). Open circles are placed at the response peak to measure time to peak (Tpeak) from the dim-flash responses. The estimated values of the amplification constant “A” and of Tpeak are indicated on the figure. C, Normalized peak response amplitude (left ordinates) and time to 40% recovery (right ordinates) versus flash intensity data measured from the response families of column A (filled symbols indicate data measured in the intensity range ∼105–106 photons per μm2, note that recovery time is plotted on a linear scale and response amplitude and flash intensity on logarithmic scales). To measure the parameter Qe (flash intensity at which response amplitude is ∼0.63 of the maximum), an exponential saturation function was fitted to the amplitude versus flash intensity data. To measure the recovery time constant, a linear regression line was fitted to recovery time versus log of flash intensity. The slope of the line per e-fold change in flash intensity estimates recovery time constant τs. D–H, Population averages (n = 9, 9, 15 for WT, Gnb3+/−, and Gnb3−/− records, respectively) for the maximum response amplitude (D), the amplification constant (E), Qe (F), light sensitivity (1/Qe; G), and time to peak (H) for WT (light gray), Gnb3+/− (dark gray), and Gnb3−/− (black) cones (n = 14 for time to peak in Gnb3−/−). **p < 0.01. In this figure, all error bars are ±2 SEMs.