OSMOSENSITIVE CL- CURRENTS AND THEIR RELEVANCE TO REGULATORY VOLUME DECREASE IN HUMAN INTESTINAL T-84 CELLS - OUTWARDLY VS. INWARDLY RECTIFYING CURRENTS

1. The swelling-activated outwardly rectifying Cl- current(I-Cl(swell) ) recorded in T-84 human intestinal cells was completely blocked by 10 mu M tamoxifen, while 300 mu M Cd2+ had no effect. 2. A ClC-2-like, i nwardly rectifying Cl- current was activated after strong hyperpolariz ation in T-84 cells. This current was completely inhibited by 300 mu M Cd2+, unaffected by 10 mu M tamoxifen, and its magnitude increased sl ightly in response to cell swelling under hyposmotic conditions. Howev er, the swelling-dependent modulation occurred only after prior activa tion by hyperpolarizing voltages. 3. T-84 cells behaved initially clos e to perfect osmometers in response to changes in external osmolalitie s between +20 and -30%. The cells underwent full regulatory volume dec rease (RVD) within 16 min when exposed to 30 or 10% hyposmotic shocks. 4. Pharmacological tools were used to determine the anionic pathway(s ) involved in RVD in T-84 cells. Tamoxifen (10 mu M), 1,9-dideoxyforsk olin (DDFSK; 100 mu M) and 4,4'-diisothiocyanatostilbene-2,2'-disulpho nic acid (DIDS; 100 mu M) blocked RVD while 300 mu M Cd2+ had no effec t upon RVD following a 30% hyposmotic shock. The RVD response was simi larly unaffected by Cd2+ when cells were exposed to a smaller (10%) hy posmotic shock. 5. In conclusion, these data show that the anionic pat hway primarily activated by cell swelling and relevant to RVD in T-84 cells is the tamoxifen-, DDFSK- and DIDS sensitive I-Cl(swell) and not the hyperpolarization-activated, Cd2+ sensitive Cl- current associate d with the ClC-2 Cl- channel.