TRPM1 is a cation-channel protein required for the normal depolarizing response of retinal ON-bipolar cells to increased illumination. In this pathway, reduced glutamate release from light-stimulated sensory cells changes signaling through mGluR6, permitting a depolarizing electric current. Thus TRPM1 participates in a synaptic response to light rather than acting as a pigment that directly absorbs the light.[ref]
TRPM1 is required for the depolarizing light response in retinal ON-bipolar cells by Catherine W. Morgans and others. Abstract: mGluR6-coupled cation channel and sign-inverting ON pathway
A 2009 experiment combined tissue localization with functional tests. Mice lacking TRPM1 retained an essentially normal initial a-wave in electroretinography, but lacked the later b-wave. The early sensory response could therefore survive while a downstream response failed. Whole-cell patch clamp recordings in retinal slices then bypassed the upstream sensory cells by chemically simulating their signal: responses were abolished in rod retinal ON-bipolar cells and strongly altered in cone retinal ON-bipolar cells.[ref]
TRPM1 is required for the depolarizing light response in retinal ON-bipolar cells by Catherine W. Morgans and others. Figures3–4: electroretinograms and chemically simulated light responses
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TRPM1 (Transient Receptor Potential Melastatin 1) is a member of the TRP (transient receptor potential) ion channel family. It is primarily known for its role in sensory reception, particularly in the context of vision and pain. TRPM1 is expressed in various tissues, including the retina, where it is localized in the photoreceptor cells, specifically in the ON-bipolar cells.