ANNEXIN-II IN EXOCYTOSIS - CATECHOLAMINE SECRETION REQUIRES THE TRANSLOCATION OF P36 TO THE SUBPLASMALEMMAL REGION IN CHROMAFFIN CELLS

Annexin II is a Ca2+-dependent membrane-binding protein present in a w ide variety of cells and tissues. Within cells, annexin II is found ei ther as a 36-kD monomer (p36) or as a heterotetrameric complex (p90) c oupled with the S-100-related protein, p11. Annexin II has been sugges ted to be involved in exocytosis as it can restore the secretory respo nsiveness of permeabilized chromaffin cells. By quantitative confocal immunofluorescence, immunoreplica analysis and immunoprecipitation, we show here the translocation of p36 from the cytosol to a subplasmalem mal Triton X-100 insoluble fraction in chromaffin cells following nico tinic stimulation. A synthetic peptide corresponding to the NH2-termin al domain of p36 which contains the phosphorylation sites was microinj ected into individual chromaffin cells and catecholamine secretion was monitored by amperometry. This peptide blocked completely the nicotin e-induced recruitment of p36 to the cell periphery and strongly inhibi ted exocytosis evoked by either nicotine or high K+. The light chain o f annexin II, p11, was selectively expressed by adrenergic chromaffin cells, and was only present in the subplasmalemmal Triton X-100 insolu ble protein fraction of both resting and stimulated cells. p11 can mod ify the Ca2+- and/or the phospholipid-binding properties of p36. We fo und that less Ca2+ was required to stimulate the translocation of p36 and to trigger exocytosis in adrenergic chromaffin cells. Our findings suggest that the translocation of p36 to the subplasmalemmal region i s an essential event in regulated exocytosis and support the idea that the presence of p11 in adrenergic cells may confer a higher Ca2+ affi nity to the exocytotic pathway in these cells.