We used the pre-embedding immunogold technique to determine the developmental changes in the subcellular localization of GIRK1, GIRK2 and GIRK3 at extrasynaptic sites (Figs 5 and 6). Distribution was quantified in the stratum radiatum for the three subunits at P5, P15 and P60. At P5, labelling for GIRK1 (Fig. 5A, B and H), GIRK2 (Fig. 5E and I) and GIRK3 (Fig. 6A, B and H) was found to be primarily associated with the endoplasmic reticulum of dendritic shafts and spine apparatus (75, 71 and 78% of all particles examined for GIRK1, GIRK2 and GIRK3, respectively). Of the immunoparticles found in the plasma membrane, most (82% of GIRK1, 81% of GIRK2 and 52% of GIRK3) were found in postsynaptic compartments, whereas the remainder (18% of GIRK1, 19% of GIRK2 and 48% of GIRK3) were found at presynaptic sites in axon terminals establishing asymmetrical synapses with dendritic spines (Figs 5H and I, and 6H).
