Subcellular compartment-specific molecular diversity of pre- and post-synaptic GABAB-activated GIRK channels in Purkinje cells |
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| Authors: | Laura Fernández-Alacid Carolina Aguado Francisco Ciruela† Ricardo Martín‡ José Colón§ María José Cabañero Martin Gassmann¶ Masahiko Watanabe Ryuichi Shigemoto†† Kevin Wickman§ Bernhard Bettler¶ José Sánchez-Prieto‡ Rafael Luján |
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| Institution: | Departamento de Ciencias Médicas, CRIB-Facultad de Medicina, Universidad Castilla-La Mancha, Albacete, Spain;
Departamento de Bioquímica i Biologia Molecular, Universitat de Barcelona, Avda. Barcelona, Spain;
Departamento de Bioquímica, Facultad de Veterinaria, Universidad Complutense, Madrid, Spain;
Department of Pharmacology, University of Minnesota, Minneapolis, Minnesota, USA;
Department of Biomedicine, Institute of Physiology, Pharmazentrum, University of Basel, Basel, Switzerland;
Department of Anatomy, Hokkaido University School of Medicine, Sapporo, Japan;
Division of Cerebral Structure, National Institute for Physiological Sciences, Myodaiji, Okazaki, SORST Japan Science and Technology Corporation, Japan |
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| Abstract: | Activation of G protein-gated inwardly-rectifying K+ (GIRK or Kir3) channels by metabotropic gamma-aminobutyric acid (B) (GABAB) receptors is an essential signalling pathway controlling neuronal excitability and synaptic transmission in the brain. To investigate the relationship between GIRK channel subunits and GABAB receptors in cerebellar Purkinje cells at post- and pre-synaptic sites, we used biochemical, functional and immunohistochemical techniques. Co-immunoprecipitation analysis demonstrated that GIRK subunits are co-assembled with GABAB receptors in the cerebellum. Immunoelectron microscopy showed that the subunit composition of GIRK channels in Purkinje cell spines is compartment-dependent. Thus, at extrasynaptic sites GIRK channels are formed by GIRK1/GIRK2/GIRK3, post-synaptic densities contain GIRK2/GIRK3 and dendritic shafts contain GIRK1/GIRK3. The post-synaptic association of GIRK subunits with GABAB receptors in Purkinje cells is supported by the subcellular regulation of the ion channel and the receptor in mutant mice. At pre-synaptic sites, GIRK channels localized to parallel fibre terminals are formed by GIRK1/GIRK2/GIRK3 and co-localize with GABAB receptors. Consistent with this morphological evidence we demonstrate their functional interaction at axon terminals in the cerebellum by showing that GIRK channels play a role in the inhibition of glutamate release by GABAB receptors. The association of GIRK channels and GABAB receptors with excitatory synapses at both post- and pre-synaptic sites indicates their intimate involvement in the modulation of glutamatergic neurotransmission in the cerebellum. |
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| Keywords: | cerebellum electron microscopy glutamate release immunohistochemistry potassium channels subunit composition |
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