Dynamical Adaptation in Photoreceptors
Figure 9
Schematic illustration of the phototransduction cascade.
Initially, photons are absorbed by rhodopsin molecules. This triggers a sequence of biochemical reactions resulting in photoreceptor hyperpolarization and calcium influx. We highlight the reaction step in which activated phosphodiesterase (red) increases the rate of conversion of cyclic GMP to GMP (green). The documented calcium feedback mechanisms (blue) include positive and negative regulations of reaction rates (denoted by the symbols + and − respectively).