title: Parathyroid hormone secretion does not respond to changes of free calcium in electropermeabilized bovine parathyroid cells, but is stimulated with phorbol ester and cyclic AMP.
abstract: The secretion of parathyroid hormone (PTH) is suppressed in bovine parathyroid cells by raised extracellular [Ca2+], and 12-0-tetradecanoyl-phorbol-13-acetate (TPA) stimulates the release of PTH from cells suppressed by high extracellular [Ca2+]. Extracellular and cytosolic free [Ca2+] are proportionally related in intact cells. To assess the role of cytosolic free [Ca2+] on PTH secretion, bovine parathyroid cells were rendered permeable by brief exposure to an intense electric field. PTH secretion was comparable at 40 nM, 500 nM, 5 microM, 28 microM, 0.5 mM and 2 mM [Ca2+] (release of total cellular PTH 3.7 +/- 0.5%, 3.9 +/- 0.4%, 3.4% +/- 0.3%, 3.9 +/- 0.4%, 3.1 +/- 0.3%, 3.5 +/- 0.7%, respectively), but the secretion was stimulated twofold (P less than 0.05 vs. control) in a dose and ATP dependent manner with TPA (100 nM) and cyclic AMP (1 mM). As a result, free [Ca2+] in the range of those observed in intact cells during regulation of PTH secretion by changes of extracellular [Ca2+] did not affect the release of PTH in permeabilized cells. The [Ca2+] independent stimulation of PTH release by TPA and cyclic AMP indicates that changes of cytosolic free [Ca2+] may represent a secondary event not related to the regulation of PTH secretion.
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D002463:Cell Membrane Permeability; D000242:Cyclic AMP / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004563:Electrochemistry; D010280:Parathyroid Glands / Q000187:drug effects / Q000378:metabolism*; D010281:Parathyroid Hormone / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D010281:Parathyroid Hormone; D000255:Adenosine Triphosphate; D000242:Cyclic AMP; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium