title: Ca2+-dependent K+ efflux regulates deoxycholate-induced apoptosis of BHK-21 and Caco-2 cells.
abstract: OBJECTIVE
  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.
authors.affiliation: Department of General and Environmental Physiology, University of Bari, Bari, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Gerbino
authors.forename: Marianna
authors.initials: M
authors.lastname: Ranieri
authors.forename: Stefania
authors.initials: S
authors.lastname: Lupo
authors.forename: Rosa
authors.initials: R
authors.lastname: Caroppo
authors.forename: Lucantonio
authors.initials: L
authors.lastname: Debellis
authors.forename: Isabella
authors.initials: I
authors.lastname: Maiellaro
authors.forename: Mariano F
authors.initials: MF
authors.lastname: Caratozzolo
authors.forename: Francesco
authors.initials: F
authors.lastname: Lopez
authors.forename: Matilde
authors.initials: M
authors.lastname: Colella