Pathways of Cl- transport in human fibroblasts

Three pathways of Cl- efflux were identified in normal human fibroblasts. Twenty percent of the total Cl- efflux is via an electrically conductive pathway with an efflux constant of 0.016 min-1. This pathway is insensitive to 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) and bumetanide but is partially inhibited by anthracene-9-carboxylic acid. Twenty-five percent of the Cl- efflux occurs via Cl- with cation cotransport having an efflux constant of 0.020 min-1. This pathway is inhibited by bumetanide and is dependent on the simultaneous presence of Na+, K+, and Cl-. Under basal conditions, the energetics of this pathway indicate that it is operating close to equilibrium. Fifty percent of the Cl- efflux occurs via an anion exchange pathway having an efflux constant of 0.040 min-1 that is inhibited by DIDS or by removal of Cl- from the extracellular medium. Together these pathways account for 95% of the total Cl- efflux.