Annexin II modulates volume-activated chloride currents in vascular endothelial cells

The membrane-associated, microfilament-binding protein annexin II is abundantly expressed in endothelial cells from calf pulmonary artery (CPAE cells). We have analyzed its role in the regulation of volume-activated chloride currents (I-Cl,I-vol) by loading the cells via the patch pipette with a peptide comprising the N-terminal 14 residues of annexin II. This sequence harbors the binding site for the intracellular annexin II ligand, p11, and the peptide interferes with the annexin II-p11 complex formation. Loading of a CPAE cell with this peptide caused a gradual decrease in the amplitude of I-Cl,I-vol during repetitive stimulations with a 28% hypotonic extracellular solution. This run down of the current was virtually absent in untreated cells and in cells that were loaded with a mutated li-amino acid peptide, which has a single amino acid replacement known to result in a more than 1000 times reduced affinity for binding to pll. We conclude that annexin II-p11 complex formation is either directly or indirectly involved in the activation of I-Cl,I-vol in endothelial cells.