2 The role of Ca+ as an internal messenger in visual transduction of vertebrate and invertebrate organisms has been explored intensely in the recent past. Since the 2 early 1970s, calcium ions and cyclic GMP (whose levels are controlled by Ca+ in vertebrates) have been recognized as important second messengers. Particularly in 2 the last decade, however, the role of Ca+ in visual transduction has been re-evalu ated and a proliferation of research has documented a multiplicity of roles. 2 It is now evident that Ca+ modulates phototransduction by acting at several 2 sites through a host of...

2 The role of Ca] as an internal messenger in visual transduction of vertebrate and invertebrate organisms has been explored intensely in the recent past. Since the 2 early 1970s, calcium ions and cyclic GMP (whose levels are controlled by Ca+ in vertebrates) have been recognized as important second messengers. Particularly in 2 the last decade, however, the role of Ca+ in visual transduction has been re-evalu- ated and a proliferation of research has documented a multiplicity of roles. 2 It is now evident that Ca+ modulates phototransduction by acting at several 2 sites through a host of...