Phototransduction: modeling the primate cone flash response

Visual Neuroscience
R D Hamer, C W Tyler

Abstract

We have developed a new model of phototransduction that accounts for the dynamics of primate and human cone flash responses in both their linear and saturating range. The model incorporates many of the known elements of the phototransduction cascade in vertebrate photoreceptors. The input stage is a new analytic expression for the activation and inactivation of cGMP-phosphodiesterase (PDE). Although the Lamb and Pugh (1992) model (of a delayed ramp for the rising phase of the PDE response in amphibian rods) provided a good fit for the first 2 log units of stimulus intensity without parameter adjustments, the remaining 4 log units of the data required nonlinear modifications of both delay and gain (slope). We show that this nonlinear behavior is a consequence of the delay approximation and develop a completely linear model to account for the rising phase of amphibian rod photocurrent responses over the full intensity range (approximately 6 log units). We use the same dynamic model to account for primate cone responses by decreasing the time constants of PDE activation and introducing an enhanced inactivation process. This PDE response activates a nonlinear calcium feedback stage that modulates guanylate cyclase synthesis of cycl...Continue Reading

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Citations

Jun 2, 2005·The Journal of General Physiology·David Holcman, Juan I Korenbrot
Oct 5, 2010·Ophthalmic & Physiological Optics : the Journal of the British College of Ophthalmic Opticians (Optometrists)·David Alleysson

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