Characterization of the distribution of G_αo in rat striatal synaptosomes and its colocalization with tyrosine hydroxylase

Dopaminergic striatal synaptosomes can be detected and isolated with a fluorescence‐activated cell sorter (FACS). In the present study, two antigens were detected simultaneously with primary antisera raised in different species and species‐specific fluorescent secondary antibodies with different emission spectra. Double‐label FACS analysis was used to determine whether tyrosine hydroxylase (TH) and the alpha subunit of G_αo (G_αo) are colocalized in striatal synaptosomes. Rabbit antibodies generated against a synthetic fragment of G_αo (corresponding to amino acids 22–35) combined with fluorescein‐conjugated secondary antibodies were used to detect G_αo‐containing striatal synaptosomes. Preadsorption of G_αo antiserum with the synthetic peptide antigen reduced labeling to the level obtained with preimmune serum. Approximately 65–75% of striatal synaptosomes were specifically labeled by G_αo antiserum. Tyrosine hydroxylase‐containing synaptosomes were detected with a mouse monoclonal antibody to TH and R‐phycoerythrin‐conjugated secondary antibody. They comprised 15–17% of total striatal synaptosomes. Double‐label studies indicated that at least 50% of TH‐containing synaptosomes also contained G_αo. These finding suggest that G_αo may not be a protein component of all striatal nerve terminals, and provide a basis for a role for G_αo in signal transduction within subpopulations of intrinsic and afferent nerve terminals, including those of nigrostriatal dopamine neurons.