Ca2+ and Extracellular Acidification Rate Responses to Parathyroid Hormone Fragments in Rat ROS 17/2 and Human SaOS-2 Cells

Abstract

To examine the importance of the N- or C-termini of PTH(1–34) the effects of truncated fragments of PTH on human receptors in osteoblast-like SaOS-2 cells 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 ), and the Cytosensor microphysiometer was used to monitor extracellular acidification 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 lines. hPTH(3–34)NH2 and other N-terminally truncated fragments did not stimulate [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 previous results in SaOS-2 cells. Potentiation by IBMX, attenuation by 8Br-cAMP and lack of effect of the PKC inhibitor chelerythrine chloride support a cAMP/PKA-mediated signal transduction pathway in ROS 17/2, while the protein kinase C pathway was predominant in SaOS-2 cells. We conclude that the intact 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.