Abstract
Purpose::
This is a preliminary investigation to assess the biochemical and physiological role of S100B modulated ROS-GC transduction system in visual transduction.
Methods::
Membranes of photoreceptor outer segments, outer plexiform layer (P1) and inner plexiform layer (P2) prepared from freshly isolated retinas of wild type (wt) and S100B KO mice were used for guanylate cyclase activity assay, Western blots and co-immunoprecipitation experiments. Sections prepared from whole retinas of the wt or S100B KO mice were used for immunohistochemical localization of S100B. Scotopic electroretinography (ERG) responses were recorded from the S100B KO and wt mice using a single-flash and double-flash paradigms.
Results::
ROS-GC activity in the membrane fractions of photoreceptor outer segments, outer plexiform (P1) and inner plexiform (P2) layers measured in the absence of Ca2+ (1 mM EGTA) is identical for the wt and S100B KO mice indicating that in the absence of Ca2+, S100B does not affect ROS-GC activity. In the presence of 0.1 mM Ca2+ ROS-GC activity is significantly lower in the KO mice than in the wt native outer segments, P1 and P2 layers indicating that Ca2+ through S100B enhances ROS-GC activity. This interpretation was supported by the reconstitution experiments where the activity in the KO mice membranes could be restored by the addition of exogenous S100B. ERG responses (a- and b-waves) were similar in the S100B KO and wt mice. The recovery of the b-wave after strong flash in the S100B KO mice occurred at least as fast as in wt mice.
Conclusions::
The results indicate that Ca2+-modulated ROS-GC-like transduction systems are present not only in native photoreceptors but also in the secondary and tertiary retinal neurons and they may be linked with the physiology of these neurons.
Keywords: calcium • retina • signal transduction: pharmacology/physiology