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Dynamical Adaptation in Photoreceptors
Figure 2
Response to single and paired flashes in the dark—comparison of data and DA model predictions.
(A) Top: Traces of recorded hyperpolarizations in a red-sensitive turtle cone, induced by light flashes delivered in the dark. Integrated flash intensities range from 41 (lowest amplitude) to 6.7·105
photons/µm2 (highest amplitude) in intervals of factors of 2.1. (Data from Fig. 19 of Ref. [14].) Bottom: DA model predictions for corresponding intensities. The dotted line represents the response to a flash 100 times more intense than the largest experimental flash. (B) Peak hyperpolarization against flash intensity for the data displayed in Fig. 2A (open circles), for a separate experiment (closed circles; data from Fig. 7 of Ref. [15]), and for the DA model predictions displayed in Fig. 2A (solid, red line). (C) Peak delay (following the input flash) against flash intensity, extracted from Fig. 2A. (Symbols are as in Fig. 2B.) (D) Parametric plot of peak delay against peak hyperpolarization (normalized by the maximum hyperpolarization). Data points (open circles) summarize several experiments (from Fig. 10 in Ref. [13]). Parameters were chosen so as to minimize the root-mean-squared error in the voltage traces, and result in faster peaks at high intensities; alternative fitting criteria could better fit the peak timing. (E) The model predicts that responses to paired flashes add non-linearly. A conditioning flash (10 ms, 560 photons/µm2/s) is presented at 
ms. A test flash of identical intensity to the conditioning flash is presented either before or after the conditioning flash, and the response is measured. The response to the conditioning flash (in the absence of any test flash) is represented as a thick, grey line, while the colored traces represent the paired flash response minus the conditioning response on its own. The test flash delivery times are indicated by small, vertical ticks of the corresponding colors. (F) Peak response to the test flash (normalized by the peak response to the conditioning flash alone) against the delay between conditioning and test flashes. Negative delays correspond to situations in which the test flash preceded the conditioning flash. Circles represent data (from Fig. 12 of Ref. [13], modified to undo a saturation correction performed there), while the solid, red line represents the DA model prediction. The DA model predictions for this figure are calculated using the parameter set BHL (see Table 2).
doi: https://doi.org/10.1371/journal.pcbi.1003289.g002