Regulation of the phosphate (Pi) concentration in UMR 106 osteoblast-like cells: effect of Pi, Na+ and K+.
Osteoblast-like cells possess Na-dependent transporters which accumulate orthophosphate (Pi) from the extracellular medium. This may be important in bone formation. Here we describe parallel measurements of Pi uptake and cellular [Pi] in such cells from the rat (UMR 106-01 and UMR 106-06) and human (OB), and in non-osteoblastic human fibroblasts (Detroit 532 (DET)). In UMR 106-01, cellular [Pi] was weakly dependent on extracellular [Pi] and higher than expected from passive transport alone. [32Pi]-uptake was inhibited by Na deprivation, but paradoxically increased on K deprivation. With Na, 87 per cent of cellular 32P was found in organic phosphorus pools after only 5 min. Na deprivation also decreased cellular [Pi], in both UMR 106-01 and DET, but the decrease was smaller than that in [32Pi]-uptake. Ouabain decreased [32Pi]-uptake and cellular [Pi] in DET, but not in UMR 106-01. Regulation of cellular [Pi] is therefore at least partly dependent on Na/Pi co-transport, but this does not seem to be an exclusive property of osteoblasts.
Department of Human Metabolism and Clinical Biochemistry, Medical School, Sheffield, U.K.
G J
GJ
Kemp
H I
HI
Khouja
A
A
Ahmado
R
R
Graham
G
G
Russell
A
A
Bevington
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D010006:Osteoblasts / Q000187:drug effects / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology; D010710:Phosphates / Q000378:metabolism* / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology*; D051381:Rats; D012964:Sodium / Q000494:pharmacology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000378:metabolism; D014407:Tumor Cells, Cultured
D010710:Phosphates; D010042:Ouabain; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium