Osmosensitive Cl− currents and their relevance to regulatory volume decrease in human intestinal T84 cells: outwardly vs. inwardly rectifying currents

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Abstract
The swelling‐activated outwardly rectifying Cl− current (ICl(swell)) recorded in T84 human intestinal cells was completely blocked by 10 μM tamoxifen, while 300 μM Cd2+ had no effect. A ClC‐2‐like, inwardly rectifying Cl− current was activated after strong hyperpolarization in T84 cells. This current was completely inhibited by 300 μM Cd2+, unaffected by 10 μM tamoxifen, and its magnitude increased slightly in response to cell swelling under hyposmotic conditions. However, the swelling‐dependent modulation occurred only after prior activation by hyperpolarizing voltages. T84 cells behaved initially close to perfect osmometers in response to changes in external osmolalities between +20 and ‐30 %. The cells underwent full regulatory volume decrease (RVD) within 16 min when exposed to 30 or 10 % hyposmotic shocks. Pharmacological tools were used to determine the anionic pathway(s) involved in RVD in T84 cells. Tamoxifen (10 μM), 1,9‐dideoxyforskolin (DDFSK; 100 μM) and 4,4′‐diisothiocyanatostilbene‐2,2′‐disulphonic acid (DIDS; 100 μM) blocked RVD while 300 μM Cd2+ had no effect upon RVD following a 30 % hyposmotic shock. The RVD response was similarly unaffected by Cd2+ when cells were exposed to a smaller (10 %) hyposmotic shock. In conclusion, these data show that the anionic pathway primarily activated by cell swelling and relevant to RVD in T84 cells is the tamoxifen‐, DDFSK‐ and DIDS‐sensitive ICl(swell) and not the hyperpolarization‐activated, Cd2+‐sensitive Cl− current associated with the ClC‐2 Cl− channel.