Profound defects in pupillary responses to light in TRPM-channel null mice: A role for TRPM channels in non-image-forming photoreception

The Nuffield Laboratory of Ophthalmology, Nuffield Department of Clinical Neurosciences, University of Oxford, Level 5-6 West Wing, John Radcliffe Hospital, Headley Way, Oxford OX3 9DU, UK.
European Journal of Neuroscience (Impact Factor: 3.18). 01/2012; 35(1):34-43. DOI: 10.1111/j.1460-9568.2011.07944.x
Source: PubMed


TRPM1 is a spontaneously active non-selective cation channel that has recently been shown to play an important role in the depolarizing light responses of ON bipolar cells. Consistent with this role, mutations in the TRPM1 gene have been identified as a principal cause of congenital stationary night blindness. However, previous microarray studies have shown that Trpm1 and Trpm3 are acutely regulated by light in the eyes of mice lacking rods and cones (rd/rd cl), a finding consistent with a role in non-image-forming photoreception. In this study we show that pupillary light responses are significantly attenuated in both Trpm1(-/-) and Trpm3(-/-) animals. Trpm1(-/-) mice exhibit a profound deficit in the pupillary response that is far in excess of that observed in mice lacking rods and cones (rd/rd cl) or melanopsin, and cannot be explained by defects in bipolar cell function alone. Immunolocalization studies suggest that TRPM1 is expressed in ON bipolar cells and also a subset of cells in the ganglion cell layer, including melanopsin-expressing photosensitive retinal ganglion cells (pRGCs). We conclude that, in addition to its role in bipolar cell signalling, TRPM1 is involved in non-image-forming responses to light and may perform a functional role within pRGCs. By contrast, TRPM3(-/-) mice display a more subtle pupillary phenotype with attenuated responses under bright light and dim light conditions. Expression of TRPM3 is detected in Muller cells and the ciliary body but is absent from pRGCs, and thus our data support an indirect role for TRPM3 in pupillary light responses.

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    • "In vivo, TRPM3 channel activity has been found to facilitate diverse cellular processes including, insulin release by pancreatic β-cells [47], mechano-sensing in vascular smooth muscle cells [48], and thermo-sensing by dorsal root ganglia neurons [49]. Recently, Trpm3-null mice were found to display an attenuated pupillary light reflex (iris constriction) under bright light and dim light conditions [50]. The abundant expression of Trpm3 in the ciliary body coupled with the requirement for sustained Ca2+ influx during ciliary muscle contraction, support the notion that Trpm3 functions in regulating pupil constriction [50]. "
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