Transretinal ERG in studying mouse rod phototransduction: Comparison with local ERG across the rod outer segments

PURPOSE. Electroretinography (ERG) is the gold standard in clinical examinations of retinal function. Corneal ERG is widely used for diagnostics, but ERG components from the inner retina complicate quantitative investigations of the phototransduction cascade. Transretinal ERG (TERG) recorded ex vivo enables pharmacologic isolation of signals generated by photoreceptor cells, establishing an appealing electrophysiologic method for diverse studies of phototransduction. Pharmacologically isolated TERG, however, contains components arising in the photoreceptor inner segments. Here, we compared simultaneously recorded TERG and local ERG across the outer segment layer (LERG-OS) to determine how consistently TERG reflects changes in the rod outer segment current signaling. METHODS. Recordings were made from dark-adapted, isolated C57BL/6J mouse retinas superfused with HEPES or bicarbonate buffered solution containing 2-mM aspartate or 20-μM DL-2-amino-4-phosphonobutyric acid to block synaptic transmission, and 50-μM BaCl₂ to block the Müller cell component. TERG responses were recorded with macroelectrodes on both sides of the retina while responses across different retinal layers were recorded with microelectrodes. RESULTS. The time-to-peak and the dominant time constant values were slightly smaller and the half-saturating stimulus was somewhat stronger in TERG compared with LERG-OS. No differences in light adaptation data were observed between the methods. LERG responses recorded across the whole photoreceptor layer were similar to those by TERG. CONCLUSIONS. TERG photoreceptor responses correspond well with the LERG-OS responses. The main differences are the nose component and slightly faster response kinetics observed by TERG. We conclude that TERG can be used for reliable quantitative investigation of phototransduction.