A Ca2+-activated (I Cl,Ca) and a swelling-activated anion current (I Cl,vol) were investigated in Ehrlich ascites tumor cells using the whole cell patch clamp technique. Large, outwardly rectifying currents were activated by an increase in the free intracellular calcium concentration ([Ca2+] i ), or by hypotonic exposure of the cells, respectively. The reversal potential of both currents was dependent on the extracellular Cl− concentration. I Cl,Ca current density increased with increasing [Ca2+] i , and this current was abolished by lowering [Ca2+] i to <1 nm using 1,2-bis-(o-aminophenoxy)ethane-N,N,N′,N′-tetra-acetic acid (BAPTA). In contrast, activation of I Cl,vol did not require an increase in [Ca2+] i . The kinetics of I Cl,Ca and I Cl,vol were different: at depolarized potentials, I Cl,Ca as activated in a [Ca2+] i - and voltage-dependent manner, while at hyperpolarized potentials, the current was deactivated. In contrast, I Cl,vol exhibited time- and voltage-dependent deactivation at depolarized potentials and reactivation at hyperpolarized potentials. The deactivation of I Cl,vol was dependent on the extracellular Mg2+ concentration. The anion permeability sequence for both currents was I − > Cl− > gluconate. I Cl,Ca was inhibited by niflumic acid (100 μm), 5-Nitro-2-(3-phenylpropylamino)benzoic acid (NPPB, 100 μm) and 4,4′-diisothiocyano-2,2′-stilbenedisulfonic acid (DIDS, 100 μm), niflumic acid being the most potent inhibitor. In contrast, I Cl,vol was unaffected by niflumic acid (100 μm), but abolished by tamoxifen (10 μm). Thus, in Ehrlich cells, separate chloride currents, I Cl,Ca and I Cl,vol, are activated by an increase in [Ca2+] i and by cell swelling, respectively.
The Journal of Membrane Biology – Springer Journals
Published: May 15, 1998
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