Desensitization of calcium messenger system in parathyroid hormone-stimulated opossum kidney cells.
We have studied the desensitization of the calcium message system to parathyroid hormone (PTH) by monitoring intracellular calcium concentration ([Ca2+]i) in an opossum kidney cell line (OKP). PTH (10(-7) M) caused a transient increase in [Ca2+]i, with an average peak height of 48.7 +/- 4.7% above baseline (n = 32). Cells stimulated with either 10(-7) or 10(-8) M PTH did not respond to a second challenge with a maximal dose (10(-7) M) of the hormone, whereas lower concentrations of PTH (10(-9) M and 10(-10) M) only partially desensitized the cells, since a [Ca2+]i transient of smaller amplitude (12.7 +/- 2.1 and 40.6 +/- 6.2% above baseline, respectively) was observed with a second stimulation. Desensitization developed within 5 min of initial hormone exposure, when PTH receptor binding was not significantly decreased. Maximal reduction of PTH binding sites (37.0 +/- 1.4%) was achieved only after 2 h. Partial desensitization was reproduced by 10(-9) M phorbol 12-myristate 13-acetate (PMA) but not by dibutyryladenosine 3',5'-cyclic monophosphate, and it was blocked by staurosporine. However, staurosporine had no effect on the complete desensitization induced by high doses of PTH. At 10(-9) M, PTH also caused a time-dependent desensitization of the adenosine 3',5'-cyclic monophosphate (cAMP) response, with maximal inhibition achieved after 2 h. PMA also decreased the cAMP response to PTH, but its inhibitory effect was less potent than that of 10(-9) M PTH. Therefore PTH induces a dose-dependent homologous desensitization of the Ca2+ message system in OKP cells, independent of receptor occupancy.(ABSTRACT TRUNCATED AT 250 WORDS)
Division of Bone and Mineral Diseases, Jewish Hospital of St. Louis, Washington University Medical Center, St. Louis, Missouri.
A
A
Fujimori
A
A
Miyauchi
K A
KA
Hruska
K J
KJ
Martin
L V
LV
Avioli
R
R
Civitelli
D000470:Alkaloids / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D002999:Clone Cells; D000242:Cyclic AMP / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D007425:Intracellular Membranes / Q000378:metabolism; D007668:Kidney / Q000166:cytology / Q000187:drug effects* / Q000502:physiology*; D009893:Opossums; D009994:Osmolar Concentration; D010281:Parathyroid Hormone / Q000378:metabolism / Q000494:pharmacology*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D015290:Second Messenger Systems; D019311:Staurosporine; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D000470:Alkaloids; D010281:Parathyroid Hormone; D000242:Cyclic AMP; D011493:Protein Kinase C; D019311:Staurosporine; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium