LOCALIZATION OF CA2-CELLS( EXTRUSION SITES IN PANCREATIC ACINAR)

We have investigated the localization of Ca2+ extrusion sites in mouse pancreatic acinar cells, Employing a new technique, in which high res olution localization of cellular Ca2+ exit is achieved by confocal mic roscopy and a Ca2+-sensitive fluorescent probe coupled to heavy dextra n to slow down diffusion of extracellular Ca2+, it is shown directly t hat the secretory pole (secretory granule area) is the major site for Ca2+ extrusion following agonist stimulation, This Ca2+ extrusion appe ars not to be a consequence of exocytosis, as assessment of secretion under our experimental conditions (low external Ca2+ concentration, ro om temperature) using the technique of monitoring quinacrine fluoresce nce shows little loss of secretory granules in spite of sustained Ca2 exit. We conclude that Ca2+ is primarily extruded by Ca2+ pumps from the secretory pole and propose that this process is useful for maintai ning a high Ca2+ concentration in the acinar lumen, which is necessary for promotion of endocytosis.