Interdependence of Ca2+ and proton movements in trout hepatocytes

Cancer Chemotherapy Specific to Acidic Nests

The realization of cancer therapeutics specific to cancer cells with less of an effect on normal tissues is our goal. Many trials have been carried out for this purpose, but this goal is still far from being realized. It was found more than 80 years ago that solid cancer nests are acidified, but in vitro studies under acidic conditions have not been extensively studied. Recently, in vitro experiments under acidic conditions were started and anti-cancer drugs specific to acidic areas have been identified. Many genes have been reported to be expressed at a high level under acidic conditions, and such genes may be potent targets for anti-cancer drugs specific to acidic nests. In this review article, recent in vitro, in vivo, and clinical achievements in anti-cancer drugs with marked efficacy under acidic conditions are summarized, and the clinical use of anti-cancer drugs specific to acidic nests is discussed.

Na+/H+ exchanger 1, Na+/Ca2+ exchanger 1 and calmodulin complex regulates interleukin 6-mediated cellular behavior of human hepatocellular carcinoma

Interleukin 6 (IL6) is a key cytokine involved in the development and progression of inflammation-associated hepatocellular carcinoma (HCC). However, the mechanisms of IL6 action on HCC remain largely unknown. Proton and Ca(2+) are two intracellular messenger ions, which are believed to play a central role in tumorigenesis and tumor progression. In this study, we found that IL6 stimulation markedly increased intracellualr pH recovery rates of human HCC cells, Huh7 and HepG2, after NH4Cl acidification, and the NH4Cl acidification induced transient intracellular Ca(2+) increases in the HCC cells. The inhibition of Na(+)/H(+) exchanger 1 (NHE1), Na(+)/Ca(2+) exchanger 1 (NCX1) and calmodulin (CaM) inhibited the IL6 stimulation-induced intracellular pH recovery increases and NH4Cl acidification-induced intracellular Ca(2+) increases. IL6 stimulation also induced the structural interaction of NHE1, NCX1 and CaM proteins. The protein expression levels of NHE1, NCX1 and CaM in native human HCC tissues were markedly higher than those in normal liver tissues. IL6 upregulated the expressions of NHE1, NCX1 and CaM in Huh7 and HepG2 cells. NHE1, NCX1 and CaM mediated the promotion of IL6 on the proliferation, migration and invasion of Huh7 and HepG2 cells and the growth of HCC in nude mice. In conclusion, IL6 activates the functional activity of NHE1 and induces the functional and structural interaction of NHE1, NCX1 and CaM. The interaction of NHE1, NCX1 and CaM mediates the effects of IL6 on human HCC.

Ionic determinants of pH of acidic compartments under hypertonic conditions in trout hepatocytes

Exposure of trout hepatocytes to hypertonicity induced a decrease in acridine orange (AO) fluorescence, indicating a corresponding decrease in pH inside the lumen of acidic compartments (pH(L)). Pre-exposure of cells to the specific V-ATPase inhibitor bafilomycin A1 (0.3 micromol l(-1)) increased AO fluorescence - unmasking H(+) leaks under steady-state conditions - and partially removed the hypertonicity-induced pH(L) decrease. The sustainability of the luminal acidification, but not the acidification itself, appeared to depend on a low K(+) and a high Cl(-) conductance under hypertonic conditions. Increasing K(+) conductance using the specific ionophore valinomycin (10 micromol l(-1)) or removal of extracellular Cl(-) after an instant drop in AO fluorescence resulted in a reversal of luminal acidity. The alkalinization measured under hypertonic conditions in the absence of Cl(-) was largely attenuated when cells were bathed in HCO(3)(-)-free medium, signifying the possible presence of Cl(-)/HCO(3)(-) exchange. Under steady-state conditions, while a slight and brief pH(L) increase was measured upon exposure of cells to valinomycin, Cl(-) removal, unexpectedly, induced a decrease in pH(L), indicating a role for extracellular Cl(-) in limiting luminal acidification. This was confirmed by the substantial pH(L) decrease measured upon exposure of cells to the anion exchanger inhibitor SITS (0.5 mmol l(-1)). Furthermore, hypertonicity-induced acidification was still noticeable in the presence of SITS. On the other hand, the hypertonicity-induced acidification was significantly reduced in the absence of extracellular Na(+) or Ca(2+). However, BAPTA-AM induced an increase in steady-state pH(L) that was independent of V-ATPase inhibition. Moreover, the BAPTA-induced alkalinization was still apparent after depletion of intracellular Ca(2+) using the Ca(2+) ionophore A23187 in Ca(2+)-free medium. We conclude that pH(L) of trout hepatocytes is sensitive to hypertonicity and ionic determinants of hypertonicity. Thus, changes in pH(L) should be considered when studying pH adaptations to hypertonic stress.