ROS-GC1/GCAP1 Signal Transduction Machinery in the Photoreceptor-Bipolar Synaptic Region

Abstract

Abstract: : Purpose:Rod outer segment membrane guanylate cyclase (ROS-GC) transduction system is composed of two parts, Ca²⁺ sensor guanylate cyclase activating protein (GCAP), and ROS-GC. The system is pivotal for the Ca²⁺-sensitive phototransduction machinery. This study was designed to examine if this system is also operational in the photoreceptor-bipolar synaptic region. Methods:A combination of biochemical analyses involving enzyme assays, reconstitution, peptide competition, cross-linking and immunocytochemical analyses has been used. Results:The results show that the GCAP1/ROS-GC1 transduction system exists in the photoreceptor synaptic (presynaptic) terminals. Thus, the presence of this system and its linkage is not unique to the phototransduction machinery. A new topographic model of ROS-GC1 transduction is proposed. In this model, the catalytic module of ROS-GC1 at its opposite ends is independently regulated by GCAP1- and S100ß-modules. GCAP1 senses the Ca²⁺ impulse and inhibits the catalytic module; S100ß senses the impulse and stimulates the catalytic module. Conclusions: ROS-GC1 acts as a bimodal Ca²⁺ signal transduction switch in the photoreceptor bipolar synapse.

Keywords: photoreceptors • calcium • signal transduction