Differential effects of tamoxifen and I? on three distinguishable chloride currents activated in T84 intestinal cells

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Abstract
The whole-cell mode of the patch-clamp technique has been used to monitor ionic currents in T84 colonic carcinoma cells. The cells were stimulated by either a cAMP cocktail, ionomycin or hypotonicity. Sizeable currents with distinct kinetics were observed after the stimulation with the different agonists. These kinetically distinct Cl− currents also presented a differential sensitivity to the anti-oestrogen Tamoxifen and to the halide I−. Tamoxifen only inhibits the volume activated Cl− current without affecting the other two. Substitution of extracellular Cl− by I− shifted the reversal potential towards more negative values both in the hypotonicity and ionomycin activated Cl− currents. The cAMP activated current responded to the Cl− substitution by I− with a blockade of both outward and inward currents, in addition to the displacement of the zero current level towards positive values. Thus, the use of these two simple tools, I− and tamoxifen, allows the distinction of Cl− channels in epithelial cells.