Stimulation by parathyroid hormone of sup 45 Ca sup 2+ uptake in osteoblast-like cells: Possible involvement of alkaline phosphatase
- Harvard School of Public Health, Boston, MA (USA)
We have investigated the actions of human PTH (hPTH-(1-34)) on the association of 45Ca2+ with two human (SaOS-2 and MG-63) and two rat (ROS 17/2.8 and UMR-106) osteoblast-like cell types. In SaOS-2 cells, hPTH-(1-34) binds to specific membrane receptors to activate adenylate cyclase. Treatment of SaOS-2 cells with hPTH-(1-34) resulted in an increase in 45Ca2+ uptake, in a dose-dependent fashion, up to 2- to 4-fold above control values. The increase was first evident at 10 min and persisted for at least 30 min. Treatment with nimodipine, a calcium channel antagonist, was without effect on the stimulatory action of PTH. A similar enhancement of cell-associated 45Ca2+ was observed when the cells were incubated with vasoactive intestinal peptide, which acts via different receptors to activate adenylate cyclase in SaOS-2 cells. Treatment with (Bu)2cAMP also induced an increase in cell-associated 45Ca2+. Pretreatment of SaOS-2 cells with hPTH-(1-34) for 4 h, which induced homologous desensitization to a second challenge with the same peptide for stimulation of cAMP production, did not attenuate the further enhancement of cell-associated 45Ca2+ by a second treatment with hPTH-(1-34). We then examined a possible relationship between alkaline phosphatase (ALPase) and 45Ca2+ uptake. SaOS-2 cells contained high levels of alkaline phosphatase activity and continuously released the enzyme into the medium. Release was enhanced by treatment with hPTH-(1-34) for 10 min. Incubation of cells with levamisole (an inhibitor of the liver/bone/kidney type of ALPase) resulted in a rapid decrease in basal and PTH-stimulated 45Ca2+ uptake, while treatment with L-Phe-Gly-Gly was without effect. Treatment of the cells with ALPase (bovine kidney) enhanced 45Ca2+ uptake. In MG-63 cells, a stimulatory effect of hPTH-(1-34) on cell-associated 45Ca2+ was also observed; however, hPTH-(1-34) did not stimulate cAMP production in MG-63 cells.
- OSTI ID:
- 7118087
- Journal Information:
- Endocrinology; (USA), Vol. 126:4; ISSN 0013-7227
- Country of Publication:
- United States
- Language:
- English
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ALKALINE PHOSPHATASE
ENZYME ACTIVITY
CALCIUM COMPOUNDS
MEMBRANE TRANSPORT
CYCLASES
PARATHORMONE
BIOCHEMICAL REACTION KINETICS
BONE CELLS
CALCIUM 45
DOSE-RESPONSE RELATIONSHIPS
MAN
PEPTIDES
RATS
RECEPTORS
TRACER TECHNIQUES
TUMOR CELLS
ALKALINE EARTH ISOTOPES
ALKALINE EARTH METAL COMPOUNDS
ANIMAL CELLS
ANIMALS
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CALCIUM ISOTOPES
CONNECTIVE TISSUE CELLS
DAYS LIVING RADIOISOTOPES
ENZYMES
ESTERASES
EVEN-ODD NUCLEI
HORMONES
HYDROLASES
INTERMEDIATE MASS NUCLEI
ISOTOPE APPLICATIONS
ISOTOPES
KINETICS
LYASES
MAMMALS
MEMBRANE PROTEINS
NUCLEI
ORGANIC COMPOUNDS
PEPTIDE HORMONES
PHOSPHATASES
PRIMATES
PROTEINS
RADIOISOTOPES
REACTION KINETICS
RODENTS
SOMATIC CELLS
VERTEBRATES
550201* - Biochemistry- Tracer Techniques