CALCIUM AND INSULIN-LIKE-GROWTH-FACTOR-I STIMULATION OF SODIUM-DEPENDENT PHOSPHATE-TRANSPORT AND PROLIFERATION OF CULTURED RAT OSTEOBLASTS

Calcium (Ca) stimulates proliferation of osteoblasts in vitro, an effe ct proposed to be mediated by IGF I, Addition of 1 mM Ca or of 1 nM IG F I to the medium (0.3 mM Ca) of a rat bone derived cell line, PyMS, s timulated not only DNA synthesis but also sodium-dependent (Na-d) phos phate (Pi) uptake, the latter, within 2 h. These cells barely express and produce IGF I. IGF binding protein-3 which inhibits IGF action dec reased neither basal nor Ca-stimulated but IGF I-stimulated Na(d)Pi tr ansport and DNA synthesis, indicating that Ca stimulated Na(d)Pi trans port and DNA synthesis independently of IGF I. The effects of Ca and I GF I on DNA synthesis were additive. 1 mu M nifedipine blocked IGF I-a nd Ca-stimulated DNA synthesis but not Na(d)Pi transport, suggesting t hat Ca influx is not mediating the Na(d)Pi transport-enhancing IGF I s ignal but is required for IGF I-induced osteoblast proliferation. (C) 1998 Academic Press.