Explaining the functional differences of rods versus cones

Light responses in carp rods and cones, and a general scheme of phototransduction cascade. (a) Photographs and the schemes of a mechanically dissociated carp rod (left) and red-sensitive cone (right). (b) A family of light responses of a rod (left) and that of a red-sensitive cone (right) recorded with a suction electrode by giving light flashes of various intensities. (c) Light intensity–response relations of a rod (open circles) and a red-sensitive cone (filled circles) responses shown in (b). ((a)–(c): Reprinted with permission from Ref 3. Copyright 2008 Elsevier). (d) A general scheme of phototransduction cascade (see details in the text).

Purification of carp rods and cones. Mechanically dissociated carp rods and cones were layered at the top of a stepwise Percoll density gradient and were centrifuged to purify them. (Reprinted with permission from Ref 4. Copyright 2001 National Academy of Sciences, USA)

Rod versus cone differences in the generation mechanisms of a light response. (a) Transducin activation in the rod and the cone membranes. Time courses of guanosine gamma thio-phosphate (GTPγS)-binding in the rod and the cone membranes without adenosine triphosphate (ATP). Time course of GTPγS-binding in the cone membranes is shown at an expanded scale (inset). (Reprinted with permission from Fig. 2 in Ref 4. Copyright 2001 National Academy of Sciences, USA). (b) Phosphodiesterase (PDE) activation and inactivation in the rod and the cone membranes. Top: PDE activity time course measured with the pH assay method in the rod (left) or the cone (right) membranes in the presence of 0.1 mM ATP. Middle: Peak PDE activities in the rod and the cone membranes as a function of test flash intensity. Activity is expressed as percent of the maximum activity measured in the rod membranes. Bottom: Half-life of activated PDE as a function of test flash intensity. The PDE half-life was determined as the time required for the recovery of the PDE activity to 50% of the peak activity. (Reprinted with permission from Ref 4. Copyright 2001 National Academy of Sciences, USA)

Rod versus cone differences in the termination mechanisms of a light response. (a) Phosphorylation time courses in the rod and the cone membranes. The inset recordings show light responses measured in carp red-sensitive cones (four cells) elicited by a light flash of the intensity similar to that used in the biochemical phosphorylation measurement in the cone membranes. (Reprinted with permission from Fig. 1 in Ref 5. Copyright 2005 National Academy of Sciences, USA). (b) Estimated in situ guanylate cyclase activity in rods and cones. (Reprinted with permission from Ref 6. Copyright 2009 National Academy of Sciences, USA)

A scheme of rod and cone retinoid cycle. (Left) Known retinoid cycle for rods. (Right) Proposed model of retinoid cycles for cones (see text for details). (Reprinted with permission from Ref 25. Copyright 2008 National Academy of Sciences, USA)