Neuronal GIRK channels have been implicated in pain and analgesia, reward, anxiety, and energy homeostasis. Functional GIRK channels have been thought to be comprised of combinations of GIRK1 and GIRK2, the role for GIRK3 is controversial. Despite the evident importance of these channels to normal physiology, surprisingly little is known about whether channels of different subunit compositions exist and their possible role in channel function and localization. We took advantage of the cerebellum, where all three neuronal GIRK channels have been detected, to look at the existence of channels of different subunit composition. Using RT-PCR and immunohistochemistry, we found differential expression of GIRK channels in different neuronal cell types. All three neuronal GIRK channels are expressed in purkinje cells and granule cells; however, there are neurons that express only GIRK1 and GIRK3 (basket cells); only GIRK3 (stellate cells); and only GIRK2 (golgi cells). Our data suggest that channels of different subunit composition exist in vivo. To study the contribution of different subunits to channel function we compared GABAB-evoked currents in wild-type and GIRK knockout hippocampal neurons. In both acutely-isolated brain slices and primary cultures, the channel mediating the GABAB response is composed of GIRK1 and GIRK2. Although, no direct contribution of GIRK3 to GABAB-evoked current was apparent, we found evidence suggesting a role of GIRK3 in the trafficking of GIRK channels. Interestingly, subunit composition not only affects function, but it also affects localization. Using immunoelectron microscopy we found that, while GIRK1 and GIRK2 were present extrasynaptically, only GIRK2 could be detected in the synaptic cleft. Furthermore, we found evidence that the coupling efficiency of the GABAB receptor to GIRK1 and GIRK2 channels depends on their co-localization into lipid microdomains. Our data indicate that channels of different subunit composition exist in vivo, and subunit composition affects both the coupling of channels to receptors and channel localization into membrane compartments.
University of Minnesota Ph.D. dissertation. December 2008. Major: Pharmacology. Advisor: Kevin D. Wickman. 1 computer file (PDF); xii, 127 pages. ill.(some col.)
Colón Sáez, José O..
Molecular diversity and localization of Girk channels in the central nervous system..
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