title: An extended Ca2+-hypothesis of visual transduction with a role for cyclic GMP.
abstract: A model is described having the following features: Light induces Ca2+ release from vertebrate rod outer segments discs via pores composed of multimeric rhodopsin. Cytoplasmic Ca2+ reversibly blocks Na+ channels of the surface membrane, with the time course of development and amplitude of the response to light being influenced by restrictions on intradiscal Ca2+ diffusion. The falling phase of response reflects a decline in cytoplasmic [Ca2+] due to a Ca2+-binding protein controlled by cyclic GMP so that its binding capacity is increased by the reduction in cytoplasmic [cyclic GMP] which follows rhodopsin bleaching.
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002463:Cell Membrane Permeability; D006152:Cyclic GMP / Q000378:metabolism*; D008954:Models, Biological; D010775:Photic Stimulation; D012243:Rhodopsin / Q000378:metabolism; D012374:Rod Cell Outer Segment / Q000378:metabolism; D014785:Vision, Ocular / Q000502:physiology*
chemical_list: D012243:Rhodopsin; D006152:Cyclic GMP; D002118:Calcium