Ca2+ and extracellular acidification rate responses to parathyroid hormonefragments in rat ROS 17/2 and human SaOS-2 cells

To examine the importance of the N- or C-termini of PTH(1-34) the effects o f truncated fragments of PTH on human receptors in osteoblast-like SaOS-2 c ells and rat receptors in rats ROS 17/2 cells were examined. Fura-2-loaded cells were used to monitor cytosolic free Ca2+ concentration ([Ca2+](i)), a nd the Cytosensor microphysiometer was used to monitor extracellular acidif ication rate (ECAR). C-terminally truncated fragments (1-31) and (1-28) of hPTH(1-34)NH2 stimulated an increase in [Ca2+](i) and ECAR in both cell lin es. hPTH(3-34)NH2 and other N-terminally truncated fragments did not stimul ate [Ca2+](i) or ECAR in either cell type. The signal transduction pathway of PTH-induced ECAR in ROS 17/2 cells was investigated to compare with prev ious results in SaOS-2 cells. Potentiation by IBMX, attenuation by 8Br-cAMP and lack of effect of the PKC inhibitor chelerythrine chloride support a c AMP/PKA-mediated signal transduction pathway in ROS 17/2, while the protein kinase C pathway was predominant in SaOS-2 cells. Ne conclude that the int act N-terminus of PTH is essential in PTH signaling mediated via either the cAMP/PKA or inositol lipid/Ca2+/PKC pathways in osteoblast-like cells. (C) 1999 Academic Press.