Osmotic swelling-provoked release of organic osmolytes in human intestinal epithelial cells

Departments of 1 Biochemistry and 2 Psychiatry, Erasmus University Medical Center, 3000 DR Rotterdam, The Netherlands Submitted 27 October 2003 ; accepted in final form 10 February 2004 Human Intestine 407 cells respond to osmotic cell swelling by the activation of Cl – - and K + -selective ionic channels, as well as by stimulating an organic osmolyte release pathway readily permeable to taurine and phosphocholine. Unlike the activation of volume-regulated anion channels (VRAC), activation of the organic osmolyte release pathway shows a lag time of 30–60 s, and its activity persists for at least 8–12 min. In contrast to VRAC activation, stimulation of organic osmolyte release did not require protein tyrosine phosphorylation, active p21 rho , or phosphatidylinositol 3-kinase activity and was insensitive to Cl – channel blockers. Treatment of the cells with putative organic anion transporter inhibitors reduced the release of taurine only partially or was found to be ineffective. The efflux was blocked by a subclass of organic cation transporter (OCT) inhibitors (cyanine-863 and decynium-22) but not by other OCT inhibitors (cimetidine, quinine, and verapamil). Brief treatment of the cells with phorbol esters potentiated the cell swelling-induced taurine efflux, whereas addition of the protein kinase C (PKC) inhibitor GF109203X largely inhibited the response, suggesting that PKC is involved. Increasing the level of intracellular Ca 2+ by using A-23187- or Ca 2+ -mobilizing hormones, however, did not affect the magnitude of the response. Taken together, the results indicate that the hypotonicity-induced efflux of organic osmolytes is independent of VRAC and involves a PKC-dependent step. regulatory volume decrease; taurine; volume-regulated anion channels; chloride channel; protein kinase C Address for reprint requests and other correspondence: B. C. Tilly, Dept. of Biochemistry, Erasmus Univ. Medical Center, PO Box 1738, 3000 DR Rotterdam, The Netherlands (E-mail: b.tilly{at}erasmusmc.nl ).