Critical processes which characterize the photocurrent of retinal rod outer segments to flash stimuli.

The chemical reactions of retinal rod outer segments (ROS) were modeled aimed at finding the critical process for the reconstruction of the photocurrent to flash stimuli. The differential equations, which were derived from the chemical reactions, were numerically integrated. According to the present model, it was found that the most critical process for the recovery of the photocurrent was the synthesis of cGMP by guanylate cyclase in the [Ca2+]i-dependent manner. The other recovery processes, such as rhodopsin phosphorylation, transducin and phosphodiesterase inactivation seemed not to be involved in the recovery of the photocurrent to flash stimuli. Finally, a recently proposed scheme in which transducin remained bound to phosphodiesterase after its activation was examined. The simulation for this scheme showed that the ROS sensitivity was greatly reduced because of the limited amplification in the transduction cascades.