Dissociation between parathyroid hormone‐stimulated cAMP and calcium increase in UMR‐106‐01 cells

We used the osteogenic sarcoma cell line, UMR‐106‐01, to determine whether the rise in free cytosolic Ca 2+ concentration ([Ca 2+ ] i ) and cellular cAMP following PTH stimulation are able to be regulated independently. For this purpose, we compared the effect of a PTH antagonist, stimulation of protein kinase C, augmentation by prostaglandins, and the time course of desensitization of the two cellular responses. Two × 10 −7 M of the PTH antagonist 8,18 Nle 34 Tyr‐bPTH(3–34) amide ([Nle, Tyr]bPTH(3–34)A) was required to inhibit 10 −9 M bPTH(1–34)‐stimulated cAMP generation by 50%. 10 −7 M bPTH(1–34) completely overcame the inhibition induced by 10 −6 M [Nle, Tyr]bPTH(3–34)A. Only 7 × 10 −8 M and 2.7 × 10 −7 M [Nle, Tyr]bPTH(3–34)A were required to half maximally inhibit the [Ca 2+ ] i increase evoked by 3 × 10 −8 and 10 −7 M bPTH(1–34), respectively. In addition, dissociation between [Ca 2+ ] i and cAMP signals was observed when modulation by protein kinase C and prostaglandins was tested. Preincubation of the cells with 10 nM TPA for 5 minutes markedly inhibited the PTH‐evoked [Ca 2+ ] i increase. Short incubation with PGF 2α augmented the PTH‐evoked [Ca 2+ ] i increase. Similar pretreatments had no effect on the PTH‐stimulated cAMP increase. Finally, preincubation with 1.5 × 10 −9 M bPTH(1–34) for 20 minutes almost completely blocked the effect of 10 −7 M bPTH(1–34) on [Ca 2+ ] i , while preincubation with 5 × 10 −9 M bPTH(1–34) for 4 hours was required to inhibit the effect of 10 −8 M bPTH(1–34) on cAMP production by 50%. The differences in the regulation of the two PTH‐stimulated cellular signaling systems, in particular, the response to antagonists and the time course of desensitization, could be at the level of the PTH receptor(s) or at a postreceptor domain. © 1992 Wiley‐Liss, Inc.