Immunocytochemical localization of protein kinase-C subtypes in anterior pituitary cells: Colocalization in hormone-containing cells reveals heterogeneity

We have examined the distribution and colocalization of protein kinase-C (PKC) in cultured rat anterior pituitary cells by light microscopic immunocytochemistry using monoclonal antibodies to group A rat brain PKC subspecies. Type I (PKCγ) was not detected in the cells, in line with the assertion that the γ-enzyme is expressed specifically in central nervous tissues. The other subspecies recognized by the antibodies (PKCβ and PKCα) were present throughout the cytoplasm in a diffused pattern, while the nuclei were apparently unstained. The number of cells stained with the antibodies in juvenile animals (12 days old) increased rapidly with age and reached a plateau between adult (5-month-old) and older (1-yr-old) rats. Type II (PKCβ) was the predominant subspecies detected in anterior pituitary cells. Double immunofluorescence staining techniques enabled the colocalization of PKC with various anterior pituitary cell types. Surprisingly, not all of the hormone-producing cells were stained with the PKC antibodies. Moreover, within the different pituitary cell types, the percentage of PKC-stained cells varied, revealing heterogeneity among the various cell populations. Thus, among somatrophs, mammotrophs, thyrotrophs, ACTH-containing cells, and gonadotrophs, only 9%, 22%, 13%, 44%, and 26%, respectively, reacted with the PKC antibodies. We suggest that activation of pituitary PKC might mobilize only a fraction of the hormone-containing cells.