AJP - Endocrinology and Metabolism, Vol 267, Issue 1 E24-E31, Copyright © 1994 by American Physiological Society
Pi transport regulation by chicken growth plate chondrocytes
C. Montessuit, J. P. Bonjour and J. Caverzasio
Department of Medicine, University Hospital, Geneva, Switzerland.
Inorganic phosphate (Pi) is a key element for the growth and mineralization
of the epiphyseal cartilage. In this study, the characteristics of the
transport of Pi in growth plate chondrocytes have been determined using
primary cultures of chicken growth plate cartilage cells. The uptake of Pi
was significantly increased in the presence of extracellular sodium. The
kinetic parameters of the saturable sodium-dependent Pi transport (NaPiT)
were determined. The Michaelis constant for Pi was 0.443 +/- 0.095 mM, and
the concentration of sodium with which half-maximal Pi transport was
observed was 48.0 +/- 8.7 mM. Stoichiometric analysis suggested that more
than one sodium ion was cotransported with each Pi molecule. NaPiT was
sensitive to inhibition by Pi analogues such as phosphonoformic acid and
arsenate. These data strongly suggest that Pi uptake by chicken growth
plate chondrocytes is a carrier-mediated process driven by the
transmembrane electrochemical gradient of sodium. Two important regulators
of biosynthetic activities of growth plate chondrocytes, insulin-like
growth factor I (IGF-I) and parathyroid hormone (PTH), selectively
regulated Pi transport. With IGF-I, maximal stimulation (117 +/- 7% above
control) was observed at doses > 5 nM, with an half-maximal effective
concentration of 0.46 +/- 0.18 nM. A significant effect was observed after
1 h of exposure and was maintained for up to 24 h. PTH increased Pi
transport with a biphasic dose-response curve. The change in NaPiT was
transient, being maximally observed after 8 h (58 +/- 8%) and unexpressed
after 24 h.(ABSTRACT TRUNCATED AT 250 WORDS)
