Serum regulates Na+/H+ exchange in Caco-2 cells by a mechanism which is dependent on F-actin

A. J.M. Watson, S. Levine, M. Donowitz, M. H. Montrose

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Regulation of Na+/H+ exchange by fetal bovine serum was studied in Caco-2 cells, an established cell line derived from a human colon carcinoma. Cells were grown as polarized monolayers on collagen-coated filters and intracellular pH measured fluorometrically with 2',7'-bis(2-carboxymethyl)-5,6-carboxyfluorescein. Na+/H+ exchange was reduced 64% when cells were deprived of serum for 4 h. In contrast to other cell types, readdition of serum for 10 min did not activate Na+/H+ exchange; however, readdition of serum for 4 h restored Na+/H+ exchange to control values. This long-term effect of serum on Na+/H+ exchange activity could not be explained by changes in intracellular buffering capacity or intracellular [Na+]. 4-h serum deprivation reduced the K(t) of the exchanger for external Na+ from 21 to 6 mM, and reduced the V(max) by 57%, but did not alter the IC50 for amiloride in the presence of 140 mM Na+. Inhibition of protein synthesis with cycloheximide (5 μM) did not alter the effect of serum removal or readdition on Na+/H+ exchange. Low temperature (13°C) completely prevented the inhibition of Na+/H+ exchange caused by the removal of serum. In addition, once Na+/H+ exchange was inhibited by serum removal at 37°C, maintaining cells at 13°C also blocked the recovery of Na+/H+ exchange caused by serum readdition. Conversely, cytochalasin D (0.1-20 μM) blocked the reduction of Na+/H+ exchange which occurred due to 4-h serum deprivation, but did not block the restoration of Na+/H+ exchange when the cells were re-exposed to serum for a further 4 h. Colchicine (20 μM) did not alter the effect of serum removal or readdition. These data suggest that serum regulates Na+/H+ exchange activity by a posttranslational mechanism which is dependent on F-actin.

Original languageEnglish (US)
Pages (from-to)956-962
Number of pages7
JournalJournal of Biological Chemistry
Issue number2
StatePublished - 1992

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology


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