Dynamics of cyclic GMP synthesis in retinal rods.
In retinal rods, Ca(2+) exerts negative feedback control on cGMP synthesis by guanylate cyclase (GC). This feedback loop was disrupted in mouse rods lacking guanylate cyclase activating proteins GCAP1 and GCAP2 (GCAPs(-/-)). Comparison of the behavior of wild-type and GCAPs(-/-) rods allowed us to investigate the role of the feedback loop in normal rod function. We have found that regulation of GC is apparently the only Ca(2+) feedback loop operating during the single photon response. Analysis of the rods' light responses and cellular dark noise suggests that GC normally responds to light-driven changes in [Ca(2+)] rapidly and highly cooperatively. Rapid feedback to GC speeds the rod's temporal responsiveness and improves its signal-to-noise ratio by minimizing fluctuations in cGMP.
D000818:Animals; D016477:Artifacts; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000502:physiology*; D002135:Calcium-Binding Proteins / Q000172:deficiency* / Q000235:genetics; D006152:Cyclic GMP / Q000096:biosynthesis*; D003623:Dark Adaptation / Q000502:physiology; D005246:Feedback / Q000502:physiology*; D006162:Guanylate Cyclase / Q000378:metabolism*; D051604:Guanylate Cyclase-Activating Proteins; D006358:Hot Temperature; D008564:Membrane Potentials / Q000502:physiology; D051379:Mice; D018345:Mice, Knockout; D010775:Photic Stimulation; D017785:Photons; D017948:Retinal Rod Photoreceptor Cells / Q000166:cytology / Q000378:metabolism*; D012243:Rhodopsin / Q000378:metabolism; D014785:Vision, Ocular / Q000502:physiology
D002135:Calcium-Binding Proteins; D051604:Guanylate Cyclase-Activating Proteins; C496737:Guca1a protein, mouse; C496740:Guca1b protein, mouse; D012243:Rhodopsin; D006162:Guanylate Cyclase; D006152:Cyclic GMP; D002118:Calcium