Phototransduction in Rods and Cones, and Beyond

  • King-Wai Yau
Conference paper
Part of the Keio University International Symposia for Life Sciences and Medicine book series (KEIO, volume 11)


Retinal rods and cones hyperpolarize to light as a result of a light-triggered cyclic guanosine monophosphate (cGMP) signaling pathway. In this phototransduction process, light activates rhodopsin, which, via the G protein transducin, stimulates a phosphodiesterase to increase cGMP hydrolysis, causing the intracellular free cGMP level to fall and cGMP-gated, nonselective cation channels that are open in darkness to close, hence producing the hyperpolarization. This closure of the cGMP-gated channels, which are Ca2+ permeable, leads to a decrease in the free Ca2+ concentration in the outer segment. This Ca2+ decrease in the light activates multiple negativefeedback mechanisms to produce light adaptation.

Key words

Retina Photoreceptor Phototransduction 


  1. 1.
    Gomez M, Nasi E (1995) Activation of light-dependent K+ channels in ciliary invertebrate photoreceptors involves cGMP but not the IP3/Ca2+ cascade. Neuron 15: 607–618CrossRefGoogle Scholar

Copyright information

© Springer-Verlag Tokyo 2003

Authors and Affiliations

  • King-Wai Yau
    • 1
  1. 1.Department of Neuroscience and Howard Hughes Medical Institute, Room 907, Preclinical Teaching BuildingJohns Hopkins University School of MedicineBaltimoreUSA

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