Trypsinization of bovine parathyroid cells abolishes Ca2+-regulated parathyroid hormone secretion.
The secretion of parathyroid hormone (PTH) is inversely related to the extracellular Ca2+ concentration (Ca2e+). To test the hypothesis that a Ca2+ sensor on the surface of parathyroid cells is involved in Ca2+-regulated PTH secretion, limited trypsinization of bovine parathyroid cells was carried out. Treatment with trypsin (1.1-10 mg/ml) inhibited, in a dose-dependent manner, PTH secretion stimulated by lowering Ca2e+ from 2.0 to 0.5 mmol/l. In control cells, activation of protein kinase C with 12-O-tetradecanoylphorbol-13-acetate (TPA) enhanced PTH secretion at 2.0 mmol Ca2e+/l but not at 0.5 mmol Ca2e+/l. In trypsinized cells, however, TPA enhanced PTH secretion at both 0.5 and 2.0 mmol Ca2e+/l. Isoproterenol-stimulated PTH secretion was maintained in trypsinized cells, but reduced cyclic AMP production revealed that some beta-adrenergic receptors were destroyed. The cytosolic free Ca2+ concentration (Ca2i+), as measured with fura-2, was raised within seconds in response to increasing Ca2e+ from 0.5 to 2.0 mmol/l and was then lowered within 1 min to a sustained plateau; the changes were the same in trypsinized and control cells. In conclusion, trypsinization of parathyroid cells abolished Ca2+-regulated PTH secretion without affecting Ca2i+.
Muff
R
R
Department of Orthopaedic Surgery, University of Zurich, Switzerland.
Fischer
J A
JA
D000818:Animals; D002118:Calcium / Q000502:physiology*; D002417:Cattle; D000242:Cyclic AMP / Q000378:metabolism; D010280:Parathyroid Glands / Q000187:drug effects* / Q000378:metabolism; D010281:Parathyroid Hormone / Q000378:metabolism*; D014357:Trypsin / Q000494:pharmacology*
D010281:Parathyroid Hormone; D000242:Cyclic AMP; D014357:Trypsin; D002118:Calcium