AJP - Regulatory, Integrative and Comparative Physiology, Vol 272, Issue 6 1904-R1911, Copyright © 1997 by American Physiological Society
Intracellular acidification inhibits opposum kidney cell phosphate uptake
N. Yanagawa and O. D. Jo
Division of Nephrology, Sepulveda Veterans Administration Medical Center, California 91343, USA.
The aim of our study is to examine the effect of intracellular pH (pHi) on
inorganic phosphate (Pi) uptake by a proximal tubular cell line, the
opposum kidney (OK) cells. The OK cell pHi (7.48 +/- 0.02; n = 12) was
altered to levels between 6.5 and 8.5 by the high-K+ nigericin method, and
cell uptakes were measured at 7.5 extracellular pH. It was found that pHi
acidification suppressed Pi uptake with a decrease in maximal reaction
rate, whereas alkalinization had no significant effect. Other
Na(+)-dependent transport systems for glucose and amino acid were not
affected by these pHi changes. The inhibition of cell Pi uptake by pHi
acidification was not prevented by protein synthesis inhibitors
(actinomycin D or cycloheximide) or by Na+/H+ exchange inhibitor
[5-(N-ethyl-N-isopropyl)-amiloride]. pHi acidification caused a significant
decrease in cellular adenosine 3',5'-cyclic monophosphate (cAMP) content,
and cAMP-dependent protein kinase inhibitor (H-89) also did not prevent
inhibition of cell Pi uptake by pHi acidification. However, pHi
acidification stimulated protein kinase C (PKC) activity and inhibition of
PKC by PKC inhibitors (bisindolylmaleimide, calphostin C, or staurosporine)
or prolonged exposure to phorbol ester abrogated the inhibitory effect of
pHi acidification on cell Pi uptake. In summary, these studies showed that
pHi acidification inhibits Pi uptake in OK cells, probably through PKC
activation. These effects of pHi acidification may thus contribute to
increase acid excretion in systemic acidosis.
