Analysis of the relationship between rod cell membrane currents and the photoreceptor component of electroretinograms using a cable model

This study presents a one-dimensional bidomain cable model for analyzing the relationship between rod membrane currents and rod electroretinogram (ERG) waveform components. The model incorporates the detailed structural and electrophysiological properties of rod photoreceptors by assuming the distribution of various ion currents. Simulation results indicate that the outer segment current (I_photo) primarily influences the photoreceptor component of ERG in low-intensity light, while the transient potential notch shape called "nose," observed under high-intensity light stimulation, is mainly attributed to the I_h current in the inner segment. In addition, capacitive currents in the outer segment play a crucial role in maintaining extracellular current loops when I_photo is inactive. These findings highlight that currents other than I_photo, such as I_h and capacitive currents, contribute significantly to the ERG waveform, particularly under high-intensity light, as theoretically suggested by Robson et al. The model successfully reproduced the experimentally measured rod ERG waveforms and their local components, providing a foundational platform for further investigation of ERG mechanisms. This enhanced understanding could lead to improved clinical applications of ERG in the diagnosis and assessment of retinal conditions. Future work will focus on refining the ion channel distribution, incorporating additional transport mechanisms, and validating the model using a broader range of experimental data to better replicate the complex electrophysiological phenomena of rod photoreceptor cells.