Effect of parathyroid hormone and parathyroid hormone fragments on the intracellular ionized calcium concentration in an osteoblast cell line

In the present study the effect of parathyroid hormone and parathyroid hormone fragments on the intracellular ionized calcium concentration in an osteoblastic cell line (UMR 106-01) is examined. In these cells the intact hormone, bPTH(1-84) and three fragments (bPTH(1-34), hPTH(1-34) and bPTH(3-34)) induce an initial increase of the ionized calcium concentration ([Ca²⁺](i)). The increase of the [Ca²⁺](i) due to bPTH(1-84) is more pronounced and of longer duration compared to the increase due to PTH fragments. For two parathyroid hormone fragments with a modified amino acid sequence ([Nle-8,Nle-18,Tyr-34]bPTH(1-34), [Nle-8,Nle-18,Tyr-34]bPTH(3-34)), no effect was found. Our observations suggest: (1) a second messenger role for intracellular ionized calcium in the action of bPTH(1-84)in osteoblasts; (2) a functional role for the COOH-terminal part in the action of bPTH(1-84); and (3) the existence of a specific part of the hormone being responsible for the increase of the intracellular ionized calcium concentration.