Lead inhibits 1,25-dihydroxyvitamin D-3 regulation of calcium metabolism in osteoblastic osteosarcoma cells (ROS 17/2.8).
We have determined the dose-response of 1,25-dihydroxyvitamin D-3 (1,25-(OH)2D3) on the intracellular free calcium-ion concentration ([Ca2+]i) in the osteoblastic osteosarcoma cells, ROS 17/2.8, using 19F-NMR and the intracellular divalent cation indicator, 1,2-bis(2-amino-5-fluorophenoxy)ethane-N,N,N',N'-tetraacetic acid (5F-BAPTA). The dose-response demonstrated an inverted U-shaped relationship with maximal elevation of [Ca2+]i at doses of 1 to 10 nM 1,25-(OH)2D3. At 10 nM, 1,25-(OH)2D3 elevated the [Ca2+]i from a control level of 118 +/- 4 nM to a peak value of 237 +/- 8 nM within 40 min. 1,25-(OH)2D3 also increased the initial rate of Ca2+ influx into ROS 17/2.8 cells, measured by 45Ca uptake, with a dose-response relationship which paralleled its effect on [Ca2+]i. Treatment of ROS 17/2.8 cells with Pb2+ at 1 and 5 microM significantly increased [Ca2+]i but significantly reduced the 1,25-(OH)2D3-induced elevation of [Ca2+]i. Simultaneous treatment of naive cells with 1,25-(OH)2D3 and Pb2+ produce little reduction of 1,25-(OH)2D3-induced 45Ca uptake while 40 min treatment with Pb2+ before addition of 1,25-(OH)2D3 significantly reduced the 1,25-(OH)2D3-induced increase in 45Ca influx. These findings suggest that Pb2+ acts by inhibiting 1,25-(OH)2D3-activation of Ca2+ channels and interferes with 1,25-(OH)2D3 regulation of Ca2+ metabolism in osteoblastic bone cells.
Schanne
F A
FA
Department of Pediatrics, Albert Einstein College of Medicine, Montefiore Medical Center, New York, NY 10467.
Gupta
R K
RK
Rosen
J F
JF
D000818:Animals; D002117:Calcitriol / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line / Q000187:drug effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D006801:Humans; D007854:Lead / Q000633:toxicity*; D010006:Osteoblasts / Q000378:metabolism*; D012516:Osteosarcoma / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D013997:Time Factors
D007854:Lead; D011493:Protein Kinase C; D002117:Calcitriol; D002118:Calcium