GIRK1 IMMUNOREACTIVITY IS PRESENT PREDOMINANTLY IN DENDRITES DENDRITIC SPINES, AND SOMATA IN THE CA1 REGION OF THE HIPPOCAMPUS

Electron microscopic analysis of the CA1 region of the rat hippocampus revealed that specific immunoreactivity (IR) for a G protein-gated, i nwardly rectifying potassium channel (GIRK1) was present exclusively i n neurons and predominantly located in spiny dendrites of pyramidal ce lls. Within stratum lacunosum-moleculare and the superficial stratum r adiatum, GIRK1-IR was often present immediately adjacent to asymmetric (excitatory-type) postsynaptic densities in dendritic spines. The sub cellular localization of GIRK1-IR in the Golgi apparatus of pyramidal cell somata and in the plasma membrane of dendrites and dendritic spin es confirms the hypothesis that GIRK1 is synthesized by pyramidal cell s and transported to the more distal dendritic processes. G protein-co upled receptor activation of a dendritic potassium conductance would a ttenuate the propagation of excitatory synaptic inputs and thereby pro duce postsynaptic inhibition. Thus, these results show that the GIRK f amily of channels joins the list of voltage-sensitive channels now kno wn to be expressed in dendritic spines.