Calcium and Phototransduction

  • Kei Nakatani
  • Chunhe Chen
  • King-Wai Yau
  • Yiannis Koutalos
Part of the Advances in Experimental Medicine and Biology book series (AEMB, volume 514)


Visual phototransduction, the conversion of incoming light to an electrical signal, takes place in the outer segments of the rod and cone photoreceptor cells. Light reduces the concentration of cGMP, which, in darkness, keeps open cationic channels present in the plasma membrane of the outer segment. Ca2+plays an important role in phototransduction by modulating the cGMP-gated channels as well as cGMP synthesis and breakdown. Ca2+is involved in a negative feedback that is essential for photoreceptor adaptation to background illumination. The effects of Ca2+on the different components of rod phototransduction have been characterized and can quantitatively account for the steady state responses of the rod cell to background illumination. The propagation of the Ca2+feedback signal from the periphery toward the center of the outer segment depends on the Ca2+diffusion coefficient, which has a value of 15±1 μm2s-1. This value shows that diffusion of Ca2+in the radial direction is quite slow providing a significant barrier in the propagation of the feedback signal. Also, because the diffusion coefficient of Ca2+is much smaller than that of cGMP, the decline of Ca2+in the longitudinal direction lags behind the propagation of excitation by the decline of cGMP.


Outer Segment Guanylate Cyclase Guanylate Cyclase Activity Rhodopsin Kinase Copyright Permission 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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Copyright information

© Springer Science+Business Media New York 2002

Authors and Affiliations

  • Kei Nakatani
    • 1
  • Chunhe Chen
    • 2
  • King-Wai Yau
    • 3
  • Yiannis Koutalos
    • 2
  1. 1.Institute of Biological SciencesUniversity of TsukubaJapan
  2. 2.Department of Physiology and BiophysicsUniversity of Colorado School of MedicineUSA
  3. 3.Departments of Neuroscience and Ophthalmology and the Howard Hughes Medical InstituteThe Johns Hopkins University School of MedicineUSA

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