Modulation of volume regulated anion current by I-Cln

I-Cln, a cytosolic protein associated with a nucleotide-sensitive chloride current, may be involved in the regulation of a volume-regulated anion curr ent (VRAC) associated with hypotonic cell swelling. We have determined the nucleic acid sequences of I-Cln from human tsA201a, colonic (T84) and myelo ma (RPMI 8826) cell lines. The amino acid sequences are highly homologous ( greater than or equal to 99%) to each other but less homologous to I-Cln pr otein from other species. Using the whole-cell patch clamp technique, we ex amined the effect of Id, protein expression levels on VRAC properties durin g a hyposmotic challenge, Overexpression of T84 or RPMI 8226-derived I-Cln protein in tsA201a cells results in a more than 9-fold increase in the rate of VRAC activation over control values, while having no effect on VRAC ina ctivation properties. Underexpression of endogenous I-Cln protein in tsA201 a cells using antisense oligonucleotides results in a more than 180-fold de crease in VRAC activation rate as compared to control values. These results indicate that I-Cln protein expression modulates VRAC activation but not i nactivation. (C) 2000 Elsevier Science B.V. All rights reserved.