DEVELOPMENTAL AND AGE-DEPENDENT CHANGES OF 28-KDA CALBINDIN-D IN THE CENTRAL NERVOUS-TISSUE DETERMINED WITH A SENSITIVE IMMUNOASSAY METHOD

For the quantitative analysis of vitamin D-dependent 28-kDa calcium-binding protein (calbindin-D) in the CNS, we have established a highly sensitive immunoassay method. The antisera were raised in rabbits with purified calbindin-D from rat kidneys, and the antibodies were purified with a calbindin-D-coupled Sepharose column. The purified antibodies were specific for calbindin-D, showing a single band on the immunoblot with the extract of rat kidney or cerebellum. The sandwich-type immunoassay system was prepared by the use of purified monospecific antibodies, and the minimum detection limit of the assay was 0.1 pg or 3.6 amol of calbindin-D, which was sufficiently sensitive for the measurement of calbindin-D content in isolated Purkinje cell bodies at the level of single cells. The average content of calbindin-D in a single Purkinje cell was 0.05 pg. Calbindin-D was detected in most of the rat tissues examined, but it was present predominantly in the kidney and CNS, especially in the cerebellum. Calbindin-D was detected at a similarly low level in the cerebral cortex, cerebellum, and brainstem of rat embryos of 15 gestational days, and it increased gradually but differently in these regions, reaching the respective adult levels by 4-5 weeks of postnatal age. In contrast, kidney calbindin-D increased sharply between 15 gestational days and 3 postnatal days, reaching the adult level by 6 days of age. Calbindin-D levels in the adult rat CNS were affected little by age, whereas the concentrations in human cerebral cortices were significantly low in the aged brain as compared with those in the young brain. However, the concentrations in various regions of cerebral cortex from patients with Alzheimer's disease showed values similar to those in the relevant regions of the age-matched control patients.