title: Blockade of visual excitation and adaptation in Limulus photoreceptor by GDP-beta-S.
abstract: Light causes both depolarization and adaptation to light in Limulus ventral photoreceptors. Both visual excitation and adaptation were blocked by guanosine 5'-O-(2-thiodiphosphate) (GDP-beta-S), a metabolically stable analog of guanosine 5'-diphosphate (GDP). However, GDP-beta-S did not block the excitation caused by injection of inositol 1,4,5-trisphosphate into the cell. These results suggest a molecular cascade of visual excitation and adaptation: Light isomerizes the visual pigment rhodopsin, which in turn activates a guanyl nucleotide-binding protein. The binding protein then stimulates production of inositol 1,4,5-trisphosphate, which causes release of calcium from the endoplasmic reticulum.
mesh_terms: D000221:Adaptation, Ocular / Q000187:drug effects; D000818:Animals; D006150:Guanine Nucleotides; D006153:Guanosine Diphosphate / Q000031:analogs & derivatives* / Q000494:pharmacology; D006737:Horseshoe Crabs / Q000502:physiology*; D015544:Inositol 1,4,5-Trisphosphate; D007295:Inositol Phosphates / Q000494:pharmacology; D010775:Photic Stimulation; D010786:Photoreceptor Cells / Q000187:drug effects / Q000502:physiology*; D013873:Thionucleotides / Q000494:pharmacology*; D014785:Vision, Ocular
chemical_list: D006150:Guanine Nucleotides; D007295:Inositol Phosphates; D013873:Thionucleotides; D006153:Guanosine Diphosphate; C023427:guanosine 5'-O-(2-thiodiphosphate); D015544:Inositol 1,4,5-Trisphosphate