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Intracellular pH regulation in hep G2 cells: Effects of epidermal growth factor, transforming growth factor‐α, and insulinlike growth factor‐II on Na + /H + exchange activity
Author(s) -
Strazzabosco Mario,
Poci Carlo,
Spirlì Carlo,
Zsembery Akos,
Granato Anna,
Massimino Maria Luisa,
Crepaldi Gaetano
Publication year - 1995
Publication title -
hepatology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.488
H-Index - 361
eISSN - 1527-3350
pISSN - 0270-9139
DOI - 10.1002/hep.1840220232
Subject(s) - intracellular , epidermal growth factor , transforming growth factor , growth factor , chemistry , endocrinology , microbiology and biotechnology , growth factor receptor inhibitor , medicine , cell growth , biochemistry , biology , receptor
Intracellular pH (pHi) plays an important role in the metabolic activation of quiescent cells after a proliferative stimulus, and Na + /H + exchange activity is required for growth in some extrahepatic tumors. To investigate intracellular acid/base homeostasis in hepatoma cells and the effects of putative liver growth factors on Na + /H + exchange activity, we have studied intracellular pH (pHi) regulation in Hep G2 cells, a well‐differentiated hepatoma cell line, both in resting conditions and after administration of epidermal growth factor (EGF), transforming growth factor‐α (TGFα), and insulinlike growth factor‐II (IGF‐II). The effects of fetal calf serum, TGFα, and amiloride on 3 H‐Thymidine incorporation were also studied. Amiloride (1 mmol/L) and external Na + removal decreased baseline pHi in both HEPES and KRB. In HEPES, cells recovered from an acid load (20 mmol/L NH 4 Cl) by an amiloride inhabitable Na + /H + exchange. In KRB, an additional, DIDS‐inhibitable, Na + ‐ and HCO 3 ‐dependent, but Cl − ‐independent acid extruder (Na:HCO 3 cotransport) was activated. No evidence was found for a C1/HCO 3 exchange acting as acid loader. Administration of EGF and TGFα, but not of IGF‐H, induced a dose‐dependent, amiloride‐inhibitable increase in baseline pHi, together with an increase in Na + /H + exchange activity, shifting to the right the JH/pHi curve. Finally, 3 H‐thymidine incorporation in Hep G2 cells, in the presence of FCS or TGFα, was strongly inhibited by amiloride. In conclusion, in Hep G2 cells, pHi is mainly regulated by Na + /H + exchange, which activity can be stimulated by EGF and TGFα, but not by IGF‐II. Administration of TGFα stimulates DNA synthesis, an effect that is blocked by amiloride, an inhibitor of Na + /H + exchanger. These data suggest that Na + /H + exchange activation may play a critical role in the growth of some hepatic tumors. (Hepatology 1995; 22:588–597.)