CYCLIC AMP-INDUCED MUCIN EXOCYTOSIS IS INDEPENDENT OF CL- MOVEMENTS IN HUMAN COLONIC EPITHELIAL-CELLS (HT29-CL.16E)

The human colonic epithelial goblet cell line HT29-CL16E was used to t est whether stimulated Cl- transport is involved in the mucin exocytot ic response to an increase in intracellular cyclic AMP by measuring in parallel the short-circuit current (Isc) and mucin exocytosis. Additi on of 50 mu M forskolin to HT29-Cl.16E cells resulted in a 2-fold stim ulation of mucin release and an increase in Isc by 20 mu A/cm(2). To e valuate the requirement for cosecretion of Cl-, the Cl- flux was alter ed by three different manipulations: (1) Cl- in the medium was replace d by the poorly transported anion gluconate; (2) basolateral Cl- influ x through the Na+-K+-2Cl(-) cotransporter was inhibited by bumetanide; and (3) an inward Cl- flux through the apical plasma membrane was gen erated by reversing the Cl- gradient. These manipulations did not chan ge the forskolin-stimulated mucin release and thereby provide evidence that Cl- movements are not required for fusion of mucin granules with the plasma membrane.