Characterization of G-protein-gated K+ channels composed of Kir3.2 subunits in dopaminergic neurons of the substantia nigra.

G-protein-gated K+ (KG) channels generate slow inhibitory postsynaptic potentials in the brain. Current opinion suggests that neuronal KG channels are heterotetramers of Kir3.1 and Kir3.2. In substantia nigra (SN), however, mRNA of Kir3.1 does not express, whereas that of Kir3.2 clearly does. Therefore, we have characterized the KG channels containing Kir3.2 subunits in SN using biochemical and immunological techniques. We found that they were composed of only Kir3.2 subunits and did not contain significant amounts of either Kir3.1 or Kir3.3. Furthermore, at least some of the KG channels in SN were assemblies of the splicing variants Kir3. 2a and Kir3.2c. The channels were localized specifically at the postsynaptic membrane on the dendrites of dopaminergic neurons. Kir3. 2c, but not Kir3.2a, could bind a PDZ domain-containing protein, PSD-95. The heterologously expressed KG channels composed of Kir3.2a plus Kir3.2c or Kir3.2a alone were activated by G-protein stimulation, but expression of Kir3.2c alone was not. This study reveals that the Kir3.2 splicing variants play distinct roles in the control of function and localization of some of the KG channels in dopaminergic neurons of SN.