[32P]Pi uptake in cultured fibroblasts and osteoblasts: most of the cellular 32P is not Pi

Biochemical Society Transactions

Graham

et al. 1990

Self Cite

Chem. Enzymol. Commicn. 1,265-274 43,83-87 256, E93-El00 168-773 -P, transport and metabolism in the cultured rat myoblast line L6. (MEMI or Du]becco's MEM with oo/o (v/v) fetal calf Serum (FCS) or Despite the physiological and clinical importance of orthophosphate (P,) in cellular metabolism, little is known about how intracellular [PI] is controlled. This is not straight-L6 cells were grown in modified , , I Abbreviations used: MEM, modified Eagle's medium; FCS, fetal horse serum (HS). P, transport was measured on the culture plate by ["PIP, uptake 151, and cellular [P,] by a sensitivc calf serum; HS. horse serum; TR. Tris-buffered Ringer.Vol. 18

mentioning

confidence: 81%

1,25-Dihydroxyvitamin D3 increases the Pi concentration in cultured osteoblasts

Ahmado

Biochemical Society Transactions

Graham

et al. 1990

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“…3b), although this incubation period is substantially longer than the half-lives of labelling [6,9,26] and turnover [35] of 2,3-BPG. Preliminary studies of this type in cultured multicompartment cells suggest that such problems are not confined to the erythrocyte [36].…”

Section: Practical Implicationsmentioning

confidence: 99%

32P-labelling anomalies in human erythrocytes. Is there more than one pool of cellular Pi?

Kemp

Khodja

et al. 1989

Biochemical Journal

1. Human erythrocytes were incubated in autologous plasma containing [32P]Pi, and sampled by a method which avoids washing the cells. 2. In experiments of up to 3 h duration, the specific radioactivity of cellular Pi stabilized at a value below that of extracellular Pi. This can be explained on the basis of a single cellular Pi pool exchanging with a large unlabelled pool of cellular organic phosphates. 3. However, a rapid initial phase of labelling, occurring within 30 s, was inconsistent with the situation described in point 2. A possible explanation is that about 1/4 of cellular Pi occurs in a separate, fast-labelling pool. 4. When the extracellular Pi concentration was doubled, most of the corresponding increase in the steady-state cellular Pi concentration was accounted for by the apparent fast-labelling Pi pool, which also doubled. 5. The observed initial rate of labelling of cellular organic phosphates [which probably occurs through the reaction catalysed by glyceraldehyde-3-phosphate dehydrogenase (E.C. 1.2.1.12)] was considerably lower than that predicted from the flux through the Embden-Meyerhof pathway. This implies that the enzyme is exposed to Pi whose specific radioactivity is lower than the mean specific radioactivity of cellular Pi, and fails to support earlier suggestions that this enzyme uses extracellular Pi. 6. In 3 h incubations, the rate of organic phosphate labelling was roughly constant throughout, even though the specific radioactivity of cellular Pi had risen slowly to a plateau. Viewed in conjunction with point 5, this again suggests some inhomogeneity in cellular Pi. 7. Cellular Pi and extracellular Pi only reached isotopic steady state after 2 days. At this stage some organic phosphates were probably still incompletely labelled. 8. We conclude that, whatever their physical or technical reasons, such labelling inhomogeneities and slow attainment of isotopic steady state may cause serious misinterpretation of results if ignored during 32P-labelling of intact cells.

“…The similarity of K,, and relative V,,, for the two components suggests that there is as yet no reason to postulate separate P, transporters for the labelling of cellular Pi and OP in these cells. Nevertheless, we discuss elsewhere factors which affect the proportions of j2P taken up into cellular Pi and OP (Kemp et al, 1989).( 1 9 8 7~) Biochern. Soc.…”

mentioning

confidence: 99%

“…However, we show elsewhere (Kemp et al, 1989) that the interpretation of such experiments is complicated by possible heterogeneity of cellular P, and by effects arising from exchange with cellular organic phosphate (OP).…”

mentioning

confidence: 99%

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Cellular Pi concentration and Pi uptake do not always change in parallel in cultured fibroblasts and osteoblasts

Kemp

Khouja

Biochemical Society Transactions

et al. 1989

Self Cite

522BIOCHEMICAL SOCIETY TRANSACTIONS respectively. The similarity of K,, and relative V,,, for the two components suggests that there is as yet no reason to postulate separate P, transporters for the labelling of cellular Pi and OP in these cells. Nevertheless, we discuss elsewhere factors which affect the proportions of j2P taken up into cellular Pi and OP (Kemp et al., 1989).( 1 9 8 7~) Biochern. Soc. Truns. 15,[382][383] ( 1 987h) c'ukij: Tissue Int. 41 (Suppl.) 48