GCAP (Guanylate Cyclase–Activating Protein)
The primary processes of vertebrate visual excitation are located in the rod and cone photoreceptor cells of the retina. Illumination of the rod and cone cells triggers a biochemical cascade leading to hyperpolarization of the cell. This conversion of a light signal into an electrical signal is called phototransduction, and in the 1970s the concept of an intracellular second messenger mediating this process was developed. Two competing hypotheses were intensively discussed, the “calcium hypothesis” and the “cGMP hypothesis” to reconcile different lines of experimental results. With the identification of a cGMP-gated cation channel (cyclic nucleotide–gated channel, CNG-channel) in the plasma membrane of rod and cone cells, the second messenger of light excitation was finally identified (for a historical overview see Luo et al. 2008). Calcium on the other hand was found to be important for the sensitivity regulation...
- Imanishi Y, Yang L, Sokal I, Filipek S, Palczewski K, Baehr W. Diversity of guanylate cyclase-activating proteins (GCAPs) in teleost fish: characterization of three novel GCAPs (GCAP4, GCAP5, GCAP7) from zebrafish (Danio rerio) and prediction of eight GCAPs (GCAP1-8) in pufferfish (Fugu rubripes). J Mol Evol. 2004;59:204–17.PubMedPubMedCentralCrossRefGoogle Scholar