A quantitative account of the activation steps involved in phototransduction in amphibian photoreceptors

T. D. Lamb, Edward N Pugh Jr

Research output: Contribution to journalArticlepeer-review

489 Scopus citations


1. We have undertaken a theoretical analysis of the steps contributing to the phototransduction cascade in vertebrate photoreceptors. We have explicitly considered only the activation steps i.e. we have not dealt with the inactivation reactions. 2. From the theoretical analysis we conclude that a single photoisomerization leads to activation of the phosphodiesterase (PDE) with a time course which approximates a delayed ramp: the delay is contributed by several short first-order delay stages. 3. We derive a a method for extracting the time course of PDE activation from the measured electrical response, and we apply this method to recordings of the photoresponse from salamander rods. The results confirm the prediction that the time course of PDE activation is a delayed ramp, with slope proportional to light intensity; the initial delay is about 10-20 ms. 4. We derive approximate analytical solutions for the electrical response of the photoreceptor to light, both for bright flashes (isotropic conditions) and for single photons (involving longitudinal diffusion of cyclic GMP in the outer segment). The response to a brief flash is predicted to follow a delayed Caussian function of time, i.e. after an initial short delay the response should begin rising in proportion to t2. Further, the response intensity relation is predicted to obey an exponential saturation. 5.These predictions are compared with experiment, and it is shown that the rising phase of the flash response is accurately described over a very wide range of intensities. We conclude that the model provides a comprehensive description of the activation steps of phototransduction at a molecular level.

Original languageEnglish (US)
Pages (from-to)719-758
Number of pages40
JournalJournal of Physiology
StatePublished - 1992
Externally publishedYes

ASJC Scopus subject areas

  • Physiology


Dive into the research topics of 'A quantitative account of the activation steps involved in phototransduction in amphibian photoreceptors'. Together they form a unique fingerprint.

Cite this