Figure 4. Electrophysiological correlates of Arr2 translocation.

(A) Electroretinogram (ERG) responses to 2 s photoequilibrating stimuli of different wavelengths in white-eyed flies (w¹¹¹⁸). M was fully photoreconverted to R one minute before each stimulus by an ultrabright orange LED. At 520 nm there was a PDA that failed to recover. Between ca. 535 and 525 nm the recovery time courses became progressively longer. (B, C) Averaged data (mean ± SEM n = 7) plotted against wavelength (B) and f_M (C): PDA, normalized to maximal PDA (at λ <515 nm) measured 40 s after the stimulus; t_½ is the time to 50% recovery of the ERG. The normalized extent of translocation measured from Arr2-GFP fluorescence is replotted from Figure 3. (D) Responses to 2 s photoequilibrating 530 nm flashes expected to induce ~50% translocation (see panel B). 1^st flashes, delivered 1 min after long wavelength illumination had fully reconverted M to R, showed a slow recovery phase as in panel A (2 example traces superimposed); responses to subsequent identical “2^nd” flashes without an intervening reconverting stimulus (green) showed accelerated decay, similar to responses to 550 nm light (orange trace) that induced negligible translocation. Inset: bargraph showing time to 50% decay (t_½: mean ± SEM, n = 9). (E) Responses to brief (4 ms) 560 nm flashes which by themselves caused negligible (<1%) R>M or M>R conversion, before (DA) or after (530 Ad, green) translocation induced by photoequilibrating 530 nm illumination. Bar graph, showing t_½ for decay, indicates that translocation induced no significant difference in response kinetics under these conditions (mean ± SEM n= 4).