Immunocytochemical localization and immunological characterization of vitamin D-dependent calcium-binding protein in the bullfrog cerebellum.

Antiserum prepared against rat renal calcium-binding protein (CaBP) was used with the unlabeled antibody peroxidase-antiperoxidase (PAP) technique to localize the 28,000 molecular weight CaBP in the cerebellum of the bullfrog, Rana catesbeiana. Whole brains of premetamorphic tadpoles and adults were fixed in Bouin's solution for 2 or 24 h and embedded in paraffin. 8-microns parasagittal sections were prepared and treated by the PAP method. Purkinje cells of the cerebellum in tadpoles and adults were specifically stained for CaBP. In the premetamorphic corpus cerebelli, the stained Purkinje cells corresponded to the precociously developed Purkinje cells described previously. In the auricular lobe region of the cerebellum mature Purkinje cells were stained. In addition, smaller stained cells were seen. The latter were presumed to be immature Purkinje cells that would mature at the time of metamorphosis. Immunoblot procedure demonstrated cross-reactivity for the ranid brains in the 28,000 molecular weight region. This immunoreactive band comigrated with the immunoreactive band observed with purified rat renal CaBP. Although the exact functional significance of CaBP is unknown at this time, our immunocytochemical and immunological findings indicate that CaBP is an excellent marker for studies of Purkinje cell maturation.