ROLE OF CAMP IN THE EXOCYTOSIS OF VACUOLA R APICAL COMPARTMENT (VAC) IN MADINDARBY CANINE KIDNEY EPITHELIAL-CELLS

The role of cAMP in the exocytosis of VACs, transient organelles in MD CK cells (5), is described. During the exocytosis of VACs, a significa nt rise of cellular levels of both total intracellular and protein-bou nd cAMP was measured. The 8-Bromo-cAMP (analog of cAMP) added to the i ncubation medium (5-50 muM), caused the exocytosis of VACs. A similar effect was observed with 3-isobutyl-1-methylxanthine. Lanthanum, that abolishes the peak of intracellular free calcium upon calcium switch, failed to block the exocytosis. 12-0-tetradecanoylphorbol-13-acetate ( TPA) induced only a modest exocytic response. 8-Bromo-cAMP induced VAC exocytosis in sparse MDCK cells grown in normal calcium medium. These data indicated that cAMP is a mediator between the extracellular sign al provided by cell-cell contacts and VAC exocytosis.