### Abstract

Purpose. The time course of recovery of rod photocurrent from a saturating flash and noise in the single-photon response are intimately related. A single model should account for both. In the case of lower vertebrate rods, a plot of the recovery function which gives the time required for the in ward photocurrent, to increase by a criterion amount from saturation at zero as a function of the number of photoisomerizations, is well described by a single straight line on linear vs. log coordinates. One interpretation, that the random lifetime of a single activated rhodopsin (R*) is exponentially distributed, leads to a well-known theoretical problem. If the time course of activated phosphodiesterase (PDE*) were controlled by that of R*., predicted single-photon responses would be too noisy. If, instead, the time course of PDE* were uncoupled from that of R*, responses would not be noisy enough. Methods. We explored a model for R* in which complete inactivation requires multiple phosphorylation steps and a final "capping" reaction. This scheme was coupled to a phototransduction model which extends the model of Lamb and Pugh to include inactivation reactions and feedback control of guanylate cyclase activity by Ca^{2+} Results. One choice of parameters gives computed single-photon responses, noise and recovery function like those reported for lower vertebrates. Another gives single-photon responses and noise like those reported for primate rods; it also gives a recovery function with two branches like that inferred from human ERG recordings. Mathematical analysis shows why this behavior obtains. Conclusions. A single model for transduction accounts for characteristics of rod responses to single photons and to super-saturating flashes.

Original language | English (US) |
---|---|

Journal | Investigative Ophthalmology and Visual Science |

Volume | 37 |

Issue number | 3 |

State | Published - Feb 15 1996 |

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### ASJC Scopus subject areas

- Ophthalmology

### Cite this

**Phototransduction in rods : A theoretical analysis of inactivation kinetics, saturation and noise.** / Tranchina, D.

Research output: Contribution to journal › Article

}

TY - JOUR

T1 - Phototransduction in rods

T2 - A theoretical analysis of inactivation kinetics, saturation and noise

AU - Tranchina, D.

PY - 1996/2/15

Y1 - 1996/2/15

N2 - Purpose. The time course of recovery of rod photocurrent from a saturating flash and noise in the single-photon response are intimately related. A single model should account for both. In the case of lower vertebrate rods, a plot of the recovery function which gives the time required for the in ward photocurrent, to increase by a criterion amount from saturation at zero as a function of the number of photoisomerizations, is well described by a single straight line on linear vs. log coordinates. One interpretation, that the random lifetime of a single activated rhodopsin (R*) is exponentially distributed, leads to a well-known theoretical problem. If the time course of activated phosphodiesterase (PDE*) were controlled by that of R*., predicted single-photon responses would be too noisy. If, instead, the time course of PDE* were uncoupled from that of R*, responses would not be noisy enough. Methods. We explored a model for R* in which complete inactivation requires multiple phosphorylation steps and a final "capping" reaction. This scheme was coupled to a phototransduction model which extends the model of Lamb and Pugh to include inactivation reactions and feedback control of guanylate cyclase activity by Ca2+ Results. One choice of parameters gives computed single-photon responses, noise and recovery function like those reported for lower vertebrates. Another gives single-photon responses and noise like those reported for primate rods; it also gives a recovery function with two branches like that inferred from human ERG recordings. Mathematical analysis shows why this behavior obtains. Conclusions. A single model for transduction accounts for characteristics of rod responses to single photons and to super-saturating flashes.

AB - Purpose. The time course of recovery of rod photocurrent from a saturating flash and noise in the single-photon response are intimately related. A single model should account for both. In the case of lower vertebrate rods, a plot of the recovery function which gives the time required for the in ward photocurrent, to increase by a criterion amount from saturation at zero as a function of the number of photoisomerizations, is well described by a single straight line on linear vs. log coordinates. One interpretation, that the random lifetime of a single activated rhodopsin (R*) is exponentially distributed, leads to a well-known theoretical problem. If the time course of activated phosphodiesterase (PDE*) were controlled by that of R*., predicted single-photon responses would be too noisy. If, instead, the time course of PDE* were uncoupled from that of R*, responses would not be noisy enough. Methods. We explored a model for R* in which complete inactivation requires multiple phosphorylation steps and a final "capping" reaction. This scheme was coupled to a phototransduction model which extends the model of Lamb and Pugh to include inactivation reactions and feedback control of guanylate cyclase activity by Ca2+ Results. One choice of parameters gives computed single-photon responses, noise and recovery function like those reported for lower vertebrates. Another gives single-photon responses and noise like those reported for primate rods; it also gives a recovery function with two branches like that inferred from human ERG recordings. Mathematical analysis shows why this behavior obtains. Conclusions. A single model for transduction accounts for characteristics of rod responses to single photons and to super-saturating flashes.

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M3 - Article

AN - SCOPUS:33750151622

VL - 37

JO - Investigative Ophthalmology and Visual Science

JF - Investigative Ophthalmology and Visual Science

SN - 0146-0404

IS - 3

ER -