Abstract
It is known that the rod network in the retina behaves as a high-pass filter to electrical signals. In the turtle and toad retinae, it was found that the time to peak of the response was shorter in rods further away from a slit of light. In the tiger salamander retina, it was shown that the voltage responses to square current injection became more transient as they travel through the rod network. In previous studies, the high-pass filtering behavior has been attributed to an inductance element, a hyperpolarization-activated current, or a K conductance activated by Ca. However, biophysical mechanism underlying the high-pass filter is not fully understood. The objective of this study is to analyze the functional roles of individual ionic currents in the temporal filtering properties of rods through computer simulations. A model of the rod photoreceptor network was developed. The model incorporates much of the known parameters in 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.In simulation, the temporal filtering properties of the rod was analyzed. The simulated result shows that single rod itself behaves as a high-pass filter. The mechanism underlying the high-pass filter was examined by changing model parameters. The result suggests that IK(Ca), ICl(Ca) and Ih are responsible for the high-pass filtering. The model also well reproduced the experimental observation that the shortening of the time to peak as the signal propagates laterally. [J Physiol Sci. 2006;56 Suppl:S174]
