Immunocytochemical localization of vitamin D-dependent calcium-binding protein (calbindin) in thyroid parafollicular cells of guinea pig.

The presence of the 28K vitamin D-dependent, calcium-binding protein (28K calbindin) was investigated by immunocytochemistry in normal thyroid glands and parathyroid glands of rats, guinea pigs, rabbits and men, as well as in human thyroid medullary carcinomas and human parathyroid adenomas. In addition, thyroid glands and parathyroid glands of rats and guinea pigs were studied after treatment with vitamin D3 injected intramuscularly at a total dose of 1.2 x 10(6) IU per 100 g body weight. 28K calbindin was found exclusively in parafollicular cells of guinea pigs and never in those of other species investigated. It was present predominantly in the cytoplasm and in lower concentration in nuclei. After vitamin D3 treatment, increased immunoreactivity of 28K calbindin was observed in the cytoplasm and, even more pronounced, in the nuclei. In normal parathyroid cells and in parathyroid tumors and medullary thyroid carcinomas, 28K calbindin was not demonstrable. Our findings suggest an important function of calbindin in the cellular calcium processing of parafollicular cells of guinea pigs.