THE ANNEXIN II-P11 COMPLEX IS INVOLVED IN REGULATED EXOCYTOSIS IN BOVINE PULMONARY-ARTERY ENDOTHELIAL-CELLS

Annexin II is a member of a multigene family of Ca2+-regulated, membra ne-binding proteins implicated through biochemical and perforated cell experiments in Ca2+-triggered secretion. Within most cells annexin II resides in a tight heterotetrameric complex with a cellular protein l igand, pll, and complex formation is mediated via the N-terminal 14 re sidues of annexin II including the N-terminal acetyl group. To analyze at the single cell level whether the annexin II-pll complex is involv ed in regulated secretion, we used membrane capacitance measurements t o follow exocytotic fusion events in bovine aortic endothelial cells m anipulated with respect to their annexin II-pll complex formation. Upo n guanosine 5'-O-(thiotriphosphate) (GTP gamma S) stimulation, the end othelial cells show a significant increase in membrane capacitance whi ch is generally preceded by a transient rise in intracellular Ca2+ and thus indicative of the occurrence of Ca2+-regulated secretion. The GT P gamma S-induced capacitance increase is markedly reduced in cells lo aded with a synthetic peptide, Acl-14, which corresponds in sequence t o the N-terminal 14 residues of annexin II in their correctly acetylat ed form and which is capable of disrupting preformed annexin II-pll co mplexes. The effect of the peptide is highly specific as the nonacetyl ated variant, N1-14, which is incapable of disrupting annexin II-pll, does not interfere with the GTP gamma S-induced increase in membrane c apacitance, These data show that intact annexin II-p11 complexes are i ndispensable for regulated exocytosis to occur in an efficient manner in endothelial cells.