Immunocytochemical Localization of Cyclic Guanosine Monophosphate-Dependent Protein Kinase in Endocrine Tissues*

Antisera have been produced against purified soluble cyclic guanosine monophosphate (cGMP) dependent-protein kinase (ATP: protein phosphotransferase EC 2.7.1.37) isolated from bovine lung. No cross-reactivity was observed between the antisera and structurally related components of cAMP-dependent protein kinases (cAMP kinase), as judged by the immunodiffusion and immunoprecipitation techniques. Immunocytochemical specificity was determined by absorption of antisera with pure antigen. The distribution of cGMP kinase has been examined in several rat tissues, using an indirect immunofluorescence technique, and compared with the immunocytochemical distribution of cGMP. In skeletal muscle, cGMP kinase was localized primarily to A bands on the muscle fiber and along the Z line in I band regions. Densitometric determinations of immunoperoxidase staining indicated that absorbance over A band areas was greater than absorbance over the I band regions. In small intestine, cGMP kinase is distributed primarily along the villus brush border membrane. In testis, cGMP kinase is observed in several cell types adjacent to the seminiferous tubular wall, including Sertoli cells and spermatogonia, as well as in association with meiotic chromosomes of pachytene spermatocytes. In the cortex of the adrenal glands from dexamethasone-suppressed rats, chronic ACTH treatment induced an increase in cGMP kinase fluorescence in nuclei. In each of the tissues examined, a striking correlation was observed between the distribution of cGMP kinase and cGMP, supporting the hypothesis that cGMP-mediated actions occur via cGMP kinases.