Differential effects of parathyroid hormone and its analogues on cytosolic calcium ion and cAMP levels in cultured rat osteoblast-like cells.
While the stimulatory effect of parathyroid hormone (PTH) on osteoblast-like cell adenylate cyclase is well known, the effect of PTH on cytosolic calcium ion ([Ca2+]i) mobilization is controversial, one group finding no effect but others reporting various increases. We investigated the effects on [Ca2+]i of synthetic rat PTH fragment 1-34 (rPTH(1-34)) and two bovine PTH analogues that inhibit PTH's stimulation of adenylate cyclase (bovine 8,18Nle, 34Tyr-PTH(3-34) and 34Tyr-PTH(7-34]. [Ca2+]i was measured before, during, and after exposure to PTH analogues in perifused, attached osteoblast-like rat osteosarcoma cells (ROS 17/2.8) that had been scrape-loaded with the luminescent photoprotein aequorin. Resting [Ca2+]i was 0.094 +/- 0.056 microM (mean +/- S.D., n = 103) and rose in a time- and dose-specific way after exposure to rPTH(1-34). At 10(-10) M rPTH(1-34), [Ca2+]i rose 100% within 30 s to a plateau; higher concentrations of PTH yielded increasing initial peaks of [Ca2+]i followed by lower plateaus. At 10(-6) M, the initial peak was 5-fold basal, or 0.64 +/- 0.07 microM. Both analogues of PTH were at least partial agonists for [Ca2+]i mobilization and did not reduce peak [Ca2+]i when co-perifused with rPTH(1-34). However, the analogues did reduce significantly rPTH(1-34)-induced cAMP accumulation and did not increase cAMP accumulation by themselves. Thus, rPTH(1-34) strongly mobilizes [Ca2+]i in ROS 17/2.8 cells, at near-physiologic concentrations. Failure of the PTH analogues to block the effect of PTH on [Ca2+]i while inhibiting the effect on cAMP accumulation suggests separate pathways for PTH activation of adenylate cyclase and mobilization of calcium.
Donahue
H J
HJ
Division of Endocrinology, Metabolism, and Internal Medicine, Mayo Clinic, Rochester, Minnesota 55905.
Fryer
M J
MJ
Eriksen
E F
EF
Heath
H
H
D000262:Adenylyl Cyclases / Q000378:metabolism; D000331:Aequorin; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D010006:Osteoblasts / Q000187:drug effects / Q000378:metabolism*; D012516:Osteosarcoma; D010281:Parathyroid Hormone / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D010446:Peptide Fragments / Q000494:pharmacology; D051381:Rats; D019379:Teriparatide; D014407:Tumor Cells, Cultured
D010281:Parathyroid Hormone; D010446:Peptide Fragments; D019379:Teriparatide; D000331:Aequorin; C025497:parathyroid hormone (3-34) amide, Nle(8,18)-Nle(34)-; C038040:parathyroid hormone (7-34)amide, Tyr(34)-; D000242:Cyclic AMP; D000262:Adenylyl Cyclases; D002118:Calcium