Parathyroid hormone, prostaglandin E2, and 1,25-dihydroxyvitamin D3 decrease the level of Na+-Ca2+ exchange protein in osteoblastic cells.
We previously described Na+-Ca2+ exchange in osteoblastic rat osteosarcoma cells (UMR-106) and demonstrated that Na+-dependent Ca2+ transport was inhibited by 24-hour treatment of cells with parathyroid hormone (PTH), prostaglandin E2 (PGE2), or 1,25(OH)2D3. To determine whether this inhibition of Na+-Ca2+ exchange is at the level of exchanger protein synthesis we have examined exchanger protein levels using immunoblot analysis. UMR-106 cells were treated for 24 hours with or without PTH, PGE2, or 1,25(OH)2D3. Plasma membrane fractions (7500 g) were obtained and proteins were separated by SDS-PAGE, transferred to nylon membranes, and immunoblotted with a polyclonal antibody to the canine cardiac Na+-Ca2+ exchanger. In rat cardiac membranes, we detected 125 and 75 kD bands, similar to findings for the canine exchanger. In the osteoblastic UMR cell membranes, a specific band was detected at 90 kD that decreased 65% after treatment of cells with PTH. Inhibition by PTH was dose dependent, was maximal with 10(-7) M PTH, and required 16-24 hour treatment time. Similar inhibition was observed after a 24 hour treatment with 10(-6) M PGE2 or 10(-8) M 1,25(OH)2D3. These results demonstrate the presence of a specific protein in UMR cells that cross-reacts with antibody directed against the cardiac Na+-Ca2+ exchanger. Thus, the previously reported inhibition of Na+-Ca2+ exchange activity by calcemic agents in osteoblasts appears to be due to regulation of exchanger protein levels in these osteoblastic cells.
Krieger
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NS
Department of Medicine, Box 675, University of Rochester School of Medicine, 601 Elmwood Avenue, Rochester, New York 14642, USA.
D000818:Animals; D001859:Bone Neoplasms; D002117:Calcitriol / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D002352:Carrier Proteins / Q000096:biosynthesis* / Q000187:drug effects; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D015232:Dinoprostone / Q000494:pharmacology*; D004285:Dogs; D007700:Kinetics; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D010006:Osteoblasts / Q000187:drug effects / Q000378:metabolism*; D012516:Osteosarcoma; D010281:Parathyroid Hormone / Q000494:pharmacology*; D051381:Rats; D019831:Sodium-Calcium Exchanger
D002352:Carrier Proteins; D010281:Parathyroid Hormone; D019831:Sodium-Calcium Exchanger; D002117:Calcitriol; D015232:Dinoprostone; D002118:Calcium