DIFFERENTIATION OF HETEROGENEOUS PHENOTYPES IN HUMAN OSTEOBLAST CULTURES IN RESPONSE TO 1,25-DIHYDROXYVITAMIN-D3

1,25(OH)2D3 (1,25-dihydroxyvitamin D3) inhibits the cell proliferation of human osteoblast-like cell cultures, but stimulates the synthesis of two of the phenotypic markers of the osteoblast, alkaline phosphata se and osteocalcin. It is not known whether all cells which synthesize alkaline phosphatase also synthesize osteocalcin in response to 1,25( OH)2D3. In this study we addressed this question by examining the resp onse of human osteoblast-like cell cultures to 1,25(OH)2D3, using conc urrent histochemical and immunochemical staining for alkaline phosphat ase and osteocalcin, respectively. The cells were grown in the presenc e or absence of 1,25(OH)2D3 (10(-9) M) for 48 h. Co-localisation of os teocalcin and alkaline phosphatase in osteoblast-like cell cultures sh owed that not all cells which synthesize osteocalcin (about 9%) in res ponse to 1,25(OH)2D3 synthesize alkaline phosphatase (about 24%) and v ice versa. There was also a proportion of osteoblast-like cells which produce both osteocalcin and alkaline phosphatase simultaneously (abou t 12%). These findings suggest that during differentiation of bone-der ived cells in cultures, in response to 1,25(OH)2D3, heterogeneous phen otypes with respect to expression of alkaline phosphatase and osteocal cin appear.