title: The TRPM1 channel in ON-bipolar cells is gated by both the α and the βγ subunits of the G-protein Go.
abstract: Transmission from photoreceptors to ON bipolar cells in mammalian retina is mediated by a sign-inverting cascade. Upon binding glutamate, the metabotropic glutamate receptor mGluR6 activates the heterotrimeric G-protein Gαoβ3γ13, and this leads to closure of the TRPM1 channel (melastatin). TRPM1 is thought to be constitutively open, but the mechanism that leads to its closure is unclear. We investigated this question in mouse rod bipolar cells by dialyzing reagents that modify the activity of either Gαo or Gβγ and then observing their effects on the basal holding current. After opening the TRPM1 channels with light, a constitutively active mutant of Gαo closed the channel, but wild-type Gαo did not. After closing the channels by dark adaptation, phosducin or inactive Gαo (both sequester Gβγ) opened the channel while the active mutant of Gαo did not. Co-immunoprecipitation showed that TRPM1 interacts with Gβ3 and with the active and inactive forms of Gαo. Furthermore, bioluminescent energy transfer assays indicated that while Gαo interacts with both the N- and the C- termini of TRPM1, Gβγ interacts only with the N-terminus. Our physiological and biochemical results suggest that both Gαo and Gβγ bind TRPM1 channels and cooperate to close them.
authors.affiliation: GHM Institute of CNS Regeneration, Jinan University, Guangzhou, 510632, China.|Co-Innovation Center of Neuroregeneration, Nantong University, Jiangsu, China.
authors.forename: Ying
authors.initials: Y
authors.lastname: Xu
authors.affiliation: Department of Neuroscience, The Scripps Research Institute, Jupiter, FL 33458, USA.
authors.forename: Cesare
authors.initials: C
authors.lastname: Orlandi
authors.affiliation: Department of Neuroscience, The Scripps Research Institute, Jupiter, FL 33458, USA.
authors.forename: Yan
authors.initials: Y
authors.lastname: Cao
authors.affiliation: GHM Institute of CNS Regeneration, Jinan University, Guangzhou, 510632, China.
authors.forename: Shengyan
authors.initials: S
authors.lastname: Yang
authors.affiliation: National Institute of Environmental Health. Sciences., Research Triangle Park, NC 27709, USA.
authors.forename: Chan-Il
authors.initials: CI
authors.lastname: Choi
authors.affiliation: National Institute of Environmental Health. Sciences., Research Triangle Park, NC 27709, USA.
authors.forename: Vijayakanth
authors.initials: V
authors.lastname: Pagadala
authors.affiliation: National Institute of Environmental Health. Sciences., Research Triangle Park, NC 27709, USA.
authors.forename: Lutz
authors.initials: L
authors.lastname: Birnbaumer
authors.affiliation: Department of Neuroscience, The Scripps Research Institute, Jupiter, FL 33458, USA.
authors.forename: Kirill A
authors.initials: KA
authors.lastname: Martemyanov
authors.affiliation: Department of Neuroscience, University of Pennsylvania, Philadelphia, PA 19104, USA.
authors.forename: Noga
authors.initials: N
authors.lastname: Vardi
mesh_terms: D000818:Animals; D002460:Cell Line; D003623:Dark Adaptation; D003624:Darkness; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D020962:Heterotrimeric GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D015640:Ion Channel Gating; D008027:Light; D051379:Mice; D023421:Models, Animal; D009154:Mutation; D019814:Myristic Acid / Q000494:pharmacology; D011485:Protein Binding; D051381:Rats; D051245:Retinal Bipolar Cells / Q000378:metabolism* / Q000528:radiation effects; D050053:TRPM Cation Channels / Q000378:metabolism*
chemical_list: D050053:TRPM Cation Channels; C116297:Trpm1 protein, mouse; D019814:Myristic Acid; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D020962:Heterotrimeric GTP-Binding Proteins