Local, nonlinear effects of cGMP and Ca2+ reduce single photon response variability in retinal rods

Autoři: Giovanni Caruso aff001;  Vsevolod V. Gurevich aff002;  Colin Klaus aff003;  Heidi Hamm aff002;  Clint L. Makino aff004;  Emmanuele DiBenedetto aff005
Působiště autorů: CNR Ist Tecnologie Applicate ai Beni Culturali, Roma, Italy aff001;  Department of Pharmacology, Vanderbilt University Medical Center, Nashville, Tennessee, Unites States of America aff002;  The Mathematical Biosciences Institute, The Ohio State University, Columbus, Ohio, United States of America aff003;  Department of Physiology and Biophysics, Boston University School of Medicine, Boston, Massachusetts, United States of America aff004;  Department of Mathematics, Vanderbilt University, Nashville, Tennessee, United States of America aff005
Vyšlo v časopise: PLoS ONE 14(12)
Kategorie: Research Article
doi: https://doi.org/10.1371/journal.pone.0225948


The single photon response (SPR) in vertebrate photoreceptors is inherently variable due to several stochastic events in the phototransduction cascade, the main one being the shutoff of photoactivated rhodopsin. Deactivation is driven by a random number of steps, each of random duration with final quenching occurring after a random delay. Nevertheless, variability of the SPR is relatively low, making the signal highly reliable. Several biophysical and mathematical mechanisms contributing to variability suppression have been examined by the authors. Here we investigate the contribution of local depletion of cGMP by PDE*, the non linear dependence of the photocurrent on cGMP, Ca2+ feedback by making use of a fully space resolved (FSR) mathematical model, applied to two species (mouse and salamander), by varying the cGMP diffusion rate severalfold and rod outer segment diameter by an order of magnitude, and by introducing new, more refined, and time dependent variability functionals. Globally well stirred (GWS) models, and to a lesser extent transversally well stirred models (TWS), underestimate the role of nonlinearities and local cGMP depletion in quenching the variability of the circulating current with respect to fully space resolved models (FSR). These distortions minimize the true extent to which SPR is stabilized by locality in cGMP depletion, nonlinear effects linking cGMP to current, and Ca2+ feedback arising from the physical separation of E* from the ion channels located on the outer shell, and the diffusion of these second messengers in the cytoplasm.

Klíčová slova:

Cytoplasm – Mass diffusivity – Photons – Photoreceptors – Salamanders – Simulation and modeling – Second messenger system – Phototransduction


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