Effect of parathyroid hormone on amino acid transport by cultured neonatal mouse calvarial bone cells.
The effect of synthetic bovine parathyroid hormone [bPTH-(1-34)] on amino acid uptake by confluent primary cultures of osteoblast-like cells isolated from neonatal mouse calvaria was studied. The uptake of proline and leucine by membrane transport Systems A, ASC, and L was discriminated on the basis of their sodium dependency and sensitivity to the system-specific amino acid analogs 2-(methylamino)-isobutyric acid (MeAIB) for System A and 2-amino-(2,2,1)-heptane-2-carboxylic acid (BCH) for System L. Treatment with 24 nM bPTH-(1-34) in serum-free EBSS for 4 hr increased the initial uptake rate of proline by 50-80% but had no effect on the uptake of leucine. Temporally, the increase in proline uptake was preceded by a 2-hr lag period and plateaued after 5-6 hr. A 5-min exposure to the hormone was sufficient to cause a significant increase in proline uptake measured 4 hr later. The magnitude of the increase was dose-related from 0.24 to 240 nM bPTH-(1-34), with the half-maximal effect occurring at 2.4 nM. Only the sodium-dependent, MeAIB-inhibitable component of proline uptake was elevated. Eadie-Hofstee analysis indicated that bPTH-(1-34) increased Vmax without changing the Km. Actinomycin D and cycloheximide prevented the hormone-stimulated increase, suggesting that RNA and protein synthesis were required. Treatment with either inhibitor alone caused a 30-35% decrease in proline transport that was not observed in the presence of bPTH-(1-34), indicating an effect not dependent on macromolecular synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)
Yee
J A
JA
Department of Cell Biology and Anatomy, Texas Tech University Health Sciences Center, Lubbock 79430.
D000818:Animals; D000831:Animals, Newborn; D001692:Biological Transport / Q000187:drug effects; D003994:Bucladesine / Q000494:pharmacology; D002478:Cells, Cultured; D003513:Cycloheximide / Q000494:pharmacology; D003609:Dactinomycin / Q000494:pharmacology; D007700:Kinetics; D007930:Leucine / Q000378:metabolism*; D051379:Mice; D010006:Osteoblasts / Q000187:drug effects / Q000378:metabolism*; D010281:Parathyroid Hormone / Q000494:pharmacology*; D010446:Peptide Fragments / Q000494:pharmacology*; D011392:Proline / Q000378:metabolism*; D019379:Teriparatide
D010281:Parathyroid Hormone; D010446:Peptide Fragments; D019379:Teriparatide; D003609:Dactinomycin; D003994:Bucladesine; D003513:Cycloheximide; D011392:Proline; D007930:Leucine