AJP - Endocrinology and Metabolism, Vol 256, Issue 1 E93-100, Copyright © 1989 by American Physiological Society
Regulation of Na-dependent Pi transport by parathyroid hormone in osteoblast-like cells
T. Selz, J. Caverzasio and J. P. Bonjour
Department of Medicine, University Hospital, Geneva, Switzerland.
In the present work we investigated the influence of parathyroid hormone
(PTH) on the transport of inorganic phosphate (Pi) in the osteoblast-like
cell line UMR-106. Pi was transferred from the extra- to the intracellular
compartment by means of a Na-dependent transport system with an apparent
binding affinity for both Pi and Na similar to that recently observed in
the osteoblast-like cell line ROS 17/2.8 (Calcif. Tissue Int. 43: 83-87,
1988). Exposure of confluent UMR-106 cells to PTH (10(-9)-10(-7) M) induced
a concentration-related stimulation of the Na-dependent Pi transport
(NaPiT). An increase in NaPiT was observed after a 1-h exposure to 10(-7) M
PTH, with the maximal response occurring at 4-6 h. (PTH, 35.6 +/- 0.3;
vehicle, 27.4 +/- 0.2 pmol.microgram DNA-1.4 min-1, P less than 0.001). The
stimulatory effect of PTH on NaPiT was not associated with a change in the
Na-dependent alanine transport. A positive correlation was observed between
the increase of NaPiT and that of cAMP in response to various
concentrations of PTH. Stimulation of cAMP by forskolin (10(-4) M) mimicked
the effect of PTH on NaPiT. Kinetic analysis of the PTH-induced stimulation
of NaPiT indicated an increase in Vmax (PTH, 226.9 +/- 6.9; vehicle, 182.9
+/- 1.9 pmol Pi/microgram DNA, P less than 0.001), with no change in Km.
The increase in NaPiT by either PTH or forskolin was followed by a
transient inhibition from 6 to 24 h that was associated with a decrease in
the Na-dependent alanine transport.(ABSTRACT TRUNCATED AT 250 WORDS)
