Frozen tissue sections as an experimental system to reveal specific binding sites for the regulatory subunit of type II cAMP-dependent protein kinase in neurons.

Specific binding sites for the regulatory subunit of type II cAMP-dependent protein kinase (RII) were revealed in neurons by an immunohistochemical approach. Fixed frozen sections of several regions of the rat central nervous system were incubated in the presence of bovine RII. Bound bovine RII was subsequently detected by an immunofluorescence procedure using antibodies that recognize bovine but not rat RII. The results indicate that RII binds with high affinity to neurons. Binding is prominent in dendrites and almost undetectable in axons and axon terminals. The morphological distribution of the RII binding sites is almost identical to that of microtubule-associated protein 2 (MAP 2) immunoreactivity. Preadsorption of RII with a MAP preparation highly enriched in MAP 2 completely abolished binding of RII to tissue sections, suggesting that the binding is mediated by MAP 2. Our results indicate that frozen sections of fixed tissues are a suitable experimental system for study of specific interactions of cellular macromolecules at a morphological level.