AJP - Renal Physiology, Vol 265, Issue 3 440-F448, Copyright © 1993 by American Physiological Society
Acute phosphate depletion inhibits the Na+/H+ antiporter in a cultured renal cell line
J. Green, O. Foellmer, C. R. Kleeman and M. M. Basic
Laboratory of Membrane Biology, Cedars-Sinai Medical Center, University of California, School of Medicine, Los Angeles 90048.
We studied the effect of acute Pi depletion on the regulation of
intracellular pH (pHi) in the OK opossum kidney cell line by using the
pH-sensitive dye 2'7'-bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF).
Cell recovery from an NH4Cl acid load in HCO3-free buffer disclosed an
Na(+)-dependent component blocked by amiloride and a smaller
Na(+)-independent component that increased on exposure of the cells to a
high-K+ buffer. After 24-h incubation of the cells in phosphate-free
medium, pHi recovery by the Na+/H+ exchanger was markedly inhibited,
whereas the Na(+)-independent pHi recovery was not affected. The inhibition
of Na+/H+ exchange was reversible on correction of cellular Pi deficit. A
similar phenomenon was observed when cellular Pi depletion was induced by
acute exposure (min) to fructose. Pi depletion shifted the pHi dependence
of the exchanger and also reduced its maximal activity. Time-course studies
revealed that the effect of Pi depletion could not be attributed to
attenuation of Na(+)-K(+)-adenosinetriphosphatase activity and resultant
diminution of the transmembrane gradient for the Na+ influx. We conclude
that acute Pi depletion in cultured proximal tubular cells leads to
reversible inhibition of the Na+/H+ exchanger. This in vitro finding may
relate to the in vivo observation of impaired HCO3 reabsorption and
bicarbonaturia in acute Pi depletion.
