Hormonal regulation of [Ca2+](i) in periosteal-derived osteoblasts: Effects of parathyroid hormone, 1,25(OH)(2)D-3 and prostaglandin E-2

The effects of hormonal modulators of osteoblast function, parathyroid horm one, 1,25(OH)(2)D-3 and prostaglandins on [Ca2+](i) in periosteal-derived o steoblasts from rat femurs have been investigated. Our results show that ap plication of parathyroid hormone PTH (10(-5) M) and prostaglandin E-2 (PGE( 2)) (4 mu M) result in a rapid heterogeneous elevation in [Ca2+](i) that, i n the case of PTH, is dependent on both extracellular and intracellular sou rces of calcium. Variable responses to treatments have been found within po pulations of cells. The PGE, response is dose dependent. Treatment with 1,2 5(OH)(2)D-3 (10(-8) M) induces a brief (60-90 sec) elevation in [Ca2+](i) t hat is almost totally abolished in EGTA-buffered Ca2+ free medium. Interact ive effects of multiple hormone treatments have been observed. Pretreatment with 1,25(OH)(2)D-3 results in near-total inhibition of the PTH and PGE, r esponses. In conclusion, modulation of [Ca2+](i) appears to play a role not only in the direct effects of osteotropic hormones on osteoblasts but also in the synergistic and antagonistic effects between circulating hormones. (C) 2000 Wiley-Liss, Inc.