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Y. Kamiyama, T. Aoyama, S. Usui, J. Zhang, S.M. Wu; Simulation Analysis of the Spatio–Temporal Filtering Properties of the Rod Network by the Ionic Current Model . Invest. Ophthalmol. Vis. Sci. 2005;46(13):4542.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: It is well known that the rod network in the retinae of many lower vertebrates behaves as a high–pass filter to small signals. In previous studies, the high–pass filtering behavior has been attributed to an inductance in the rod membrane model (Detwiler et al. 1978), but the physiological mechanism underlying this behavior is not fully understood. The objective of this study is to analyze the functional roles of individual ionic currents in shaping the light responses of rods through computer simulations. Methods: We have developed a model of the rod photoreceptor network that accounts for the dynamics of light responses observed in rods. The model incorporates much of the known parameters in lower vertebrate rod photoreceptors, i.e., the phototransduction cascade in the outer segment, membrane ionic currents (ICa, IKv, IK(Ca), Ih, ICl(Ca)), intracellular calcium system and electrical junctions between rods. Results: Simulations with dim, slit–shaped flashes of light produced that the rod network behaves as a high–pass temporal filter to laterally spreading signals. Therefore, the underlying mechanisms of the high–pass filtering are presented in the model. We have analyzed all components in the model and found that the high–pass filtering is disappeared by blocking the calcium dependent currents, IK(Ca), ICl(Ca). We also found that the high–pass filtering to bright lights is generated by the hyperpolarization–activated current, Ih. Conclusions: The present results suggest that there are at least two different mechanisms are involved in the high–pass filtering of the rod photoreceptors, one is Ca–dependent mechanism and the other is Ih.
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