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  • Title: Ca2+-dependent K+ efflux regulates deoxycholate-induced apoptosis of BHK-21 and Caco-2 cells.
    Author: Gerbino A, Ranieri M, Lupo S, Caroppo R, Debellis L, Maiellaro I, Caratozzolo MF, Lopez F, Colella M.
    Journal: Gastroenterology; 2009 Sep; 137(3):955-64, 964.e1-2. PubMed ID: 19328800.
    Abstract:
    BACKGROUND & AIMS: Deoxycholate (DC) has proapoptotic and tumorigenic effects in different cell types of the gastrointestinal tract. Exposure of BHK-21 (stromal) cells to DC induces Ca(2+) entry at the plasma membrane, which affects intracellular Ca(2+) signaling. We assessed whether DC-induced increases in [Ca(2+)] can impinge on plasma membrane properties (eg, ionic conductances) involved in cell apoptosis. METHODS: Single- and double-barreled microelectrodes were used to measure membrane potential (V(m)) and extracellular [K(+)] in BHK-21 fibroblasts and Caco-2 colon carcinoma cells. Apoptosis was assessed by Hoechst labeling, propidium iodide staining, and caspase-3 and caspase-7 assays. RESULTS: DC-induced cell membrane hyperpolarization was directly measured with intracellular microelectrodes in both cell lines. Diverse Ca(2+) mobilizing agents, such as membrane receptor agonists, an inhibitor of the sarco/endoplasmic reticulum Ca(2+) adenosine triphosphatase and a Ca(2+) ionophore, also induced increases in V(m). Removal of extracellular Ca(2+) reduced the agonist- and DC-induced membrane hyperpolarization by approximately 15% and 60%, respectively. These findings indicate a prominent role for Ca(2+) entry at the plasma membrane in the action of this bile salt. Blockade of Ca(2+)-activated K(+) conductances by charybdotoxin and apamin reduced DC-induced hyperpolarization by 75% and 64% in BHK-21 and Caco-2 cells, respectively. These inhibitors also reduced the DC-induced increase in extracellular [K(+)] by 75% and cell apoptosis by approximately 50% in both cell lines. CONCLUSIONS: Ca(2+)-dependent K(+) conductance is an important regulator of DC-induced apoptosis in stromal and colon cancer cells.
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