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The TRPM1 channel in ON-bipolar cells is gated by both the ? and the ?? 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 G?o?3?13, 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 G?o or G?? and then observing their effects on the basal holding current. After opening the TRPM1 channels with light, a constitutively active mutant of G?o closed the channel, but wild-type G?o did not. After closing the channels by dark adaptation, phosducin or inactive G?o (both sequester G??) opened the channel while the active mutant of G?o did not. Co-immunoprecipitation showed that TRPM1 interacts with G?3 and with the active and inactive forms of G?o. Furthermore, bioluminescent energy transfer assays indicated that while G?o interacts with both the N- and the C- termini of TRPM1, G?? interacts only with the N-terminus. Our physiological and biochemical results suggest that both G?o and G?? bind TRPM1 channels and cooperate to close them.

SUBMITTER: Xu Y

PROVIDER: S-EPMC4756708 | biostudies-literature | 2016 Feb

REPOSITORIES: biostudies-literature

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The TRPM1 channel in ON-bipolar cells is gated by both the α and the βγ subunits of the G-protein Go.

Xu Ying Y Orlandi Cesare C Cao Yan Y Yang Shengyan S Choi Chan-Il CI Pagadala Vijayakanth V Birnbaumer Lutz L Martemyanov Kirill A KA Vardi Noga N

Scientific reports 20160217

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 ei ...[more]

PMID: 26883481

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Project description:As with other elements of the peripheral auditory system, spiral ganglion neurons display specializations that vary as a function of location along the tonotopic axis. Previous work has shown that voltage-gated K(+) channels and synaptic proteins show graded changes in their density that confers rapid responsiveness to neurons in the high frequency, basal region of the cochlea and slower, more maintained responsiveness to neurons in the low frequency, apical region of the cochlea. In order to understand how voltage-gated calcium channels (VGCCs) may contribute to these diverse phenotypes, we identified the VGCC α-subunits expressed in the ganglion, investigated aspects of Ca(2+)-dependent neuronal firing patterns, and mapped the intracellular and intercellular distributions of seven VGCC α-subunits in the spiral ganglion in vitro. Initial experiments with qRT-PCR showed that eight of the ten known VGCC α-subunits were expressed in the ganglion and electrophysiological analysis revealed firing patterns that were consistent with the presence of both LVA and HVA Ca(2+) channels. Moreover, we were able to study seven of the α-subunits with immunocytochemistry, and we found that all were present in spiral ganglion neurons, three of which were neuron-specific (Ca(V)1.3, Ca(V)2.2, and Ca(V)3.3). Further characterization of neuron-specific α-subunits showed that Ca(V)1.3 and Ca(V)3.3 were tonotopically-distributed, whereas Ca(V)2.2 was uniformly distributed in apical and basal neurons. Multiple VGCC α-subunits were also immunolocalized to Schwann cells, having distinct intracellular localizations, and, significantly, appearing to distinguish putative compact (Ca(V)2.3, Ca(V)3.1) from loose (Ca(V)1.2) myelin. Electrophysiological evaluation of spiral ganglion neurons in the presence of TEA revealed Ca(2+) plateau potentials with slopes that varied proportionately with the cochlear region from which neurons were isolated. Because afterhyperpolarizations were minimal or absent under these conditions, we hypothesize that differential density and/or kinetics of one or more of the VGCC α-subunits could account for observed tonotopic differences. These experiments have set the stage for defining the clear multiplicity of functional control in neurons and Schwann cells of the spiral ganglion.

Dataset Information

The TRPM1 channel in ON-bipolar cells is gated by both the ? and the ?? subunits of the G-protein Go.

Publications

The TRPM1 channel in ON-bipolar cells is gated by both the α and the βγ subunits of the G-protein Go.

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