Belan P V, Gerasimenko O V, Tepikin A V, Petersen O H
Medical Research Council Secretory Control Research Group, Physiological Laboratory, University of Liverpool, United Kingdom.
J Biol Chem. 1996 Mar 29;271(13):7615-9. doi: 10.1074/jbc.271.13.7615.
We have investigated the localization of Ca2+ extrusion sites in mouse pancreatic acinar cells. Employing a new technique, in which high resolution localization of cellular Ca2+ exit is achieved by confocal microscopy and a Ca2+-sensitive fluorescent probe coupled to heavy dextran to slow down diffusion of extracellular Ca2+, it is shown directly that the secretory pole (secretory granule area) is the major site for Ca2+ extrusion following agonist stimulation. This Ca2+ extrusion appears not to be a consequence of exocytosis, as assessment of secretion under our experimental conditions (low external Ca2+ concentration, room temperature) using the technique of monitoring quinacrine fluorescence 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 maintaining a high Ca2+ concentration in the acinar lumen, which is necessary for promotion of endocytosis.
