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)
Fujimori
A
A
Division of Bone and Mineral Diseases, Jewish Hospital of St. Louis, Washington University Medical Center, St. Louis, Missouri.
Miyauchi
A
A
Hruska
K A
KA
Martin
K J
KJ
Avioli
L V
LV
Civitelli
R
R
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