C. Montessuit et al., P-I TRANSPORT REGULATION BY CHICKEN GROWTH-PLATE CHONDROCYTES, The American journal of physiology, 267(1), 1994, pp. 50000024-50000031
Inorganic phosphate (P-i) is a key element for the growth and minerali
zation of the epiphyseal cartilage. In this study, the characteristics
of the transport of P-i in growth plate chondrocytes have been determ
ined using primary cultures of chicken growth plate cartilage cells. T
he uptake of P-i was significantly increased in the presence of extrac
ellular sodium. The kinetic parameters of the saturable sodium-depende
nt P-i transport (NaPiT) were determined. The Michaelis constant for P
-i was 0.443 +/- 0.095 mM, and the concentration of sodium with which
half-maximal P-i transport was observed was 48.0 +/- 8.7 mM. Stoichiom
etric analysis suggested that more than one sodium ion was cotransport
ed with each P-i molecule. NaPiT was sensitive to inhibition by P-i an
alogues such as phosphonoformic acid and arsenate. These data strongly
suggest that P-i uptake by chicken growth plate chondrocytes is a car
rier-mediated process driven by the transmembrane electrochemical grad
ient of sodium. Two important regulators of biosynthetic activities of
growth plate chondrocytes, insulin-like growth factor I (IGF-I) and p
arathyroid hormone (PTH), selectively regulated P-i transport. With IG
F-I, maximal stimulation (117 +/- 7% above control) was observed at do
ses >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 P-i transport with a biphasi
c dose-response curve. The change in NaPiT was transient, being maxima
lly observed after 8 h (58 +/- 8%) and unexpressed after 24 h. In conc
lusion, P-i transport in growth plate chondrocytes is a carrier-mediat
ed process that is selectively stimulated by IGF-I and PTH, two physio
logical regulators of growth plate chondrocyte development.