DUAL ROLE FOR PROTEIN KINASE-C-ALPHA AS A REGULATOR OF ION SECRETION IN THE HT29CL.19A HUMAN COLONIC CELL-LINE

The involvement of protein kinase C (PKC) in the regulation of intestinal ion secretion was studied in polarized monolayers of the HT29cl.19A human colon carcinoma cell line. Carbachol, phorbol esters [PMA (phorbol 12-myristate 13-acetate) and PDB (phorbol 12,13-dibutyrate)] and 8-bromo cyclic AMP (8-Br-cAMP) induced Cl secretion, as measured by a rise in the short-circuit current (I(SC)). The electrical response to carbachol coincided with a transient translocation of PKC alpha from the soluble to the particulate fraction. The carbachol-, PDB- and 8-Br-cAMP-induced I(SC) responses were inhibited by pretreatment of the cells with PMA (0.5-mu-M) for 2h, a time period in which PKC alpha, beta-1 and gamma-levels were not changed. As shown by Rb-86+ and I-125+ efflux studies, the main targets for this inhibition were basolateral K+ transporters rather than apical Cl- channels. Prolonged exposure to PMA (24 h) led to a 60% recovery of the 8-Br-cAMP response, but not of the carbachol- or PDB-provoked secretion. As shown by immunoblotting with PKC-isoenzyme-specific antisera, the recovery of the 8-Br-cAMP response coincided with the down-regulation of PKC-alpha, whereas the levels of PKC-beta-1 and gamma were unmodified. These results suggest that PKC-alpha, but not PKC-beta-1 or gamma, is involved in both acute stimulation and chronic inhibition of ion secretion in the HT29cl.19A colonic cell line.