Localization of Ca2+ extrusion sites in pancreatic acinar cells.
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.
Belan
P V
PV
Medical Research Council Secretory Control Research Group, Physiological Laboratory, University of Liverpool, United Kingdom.
Gerasimenko
O V
OV
Tepikin
A V
AV
Petersen
O H
OH
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D003594:Cytoplasmic Granules / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure; D005089:Exocytosis; D007700:Kinetics; D051379:Mice; D018613:Microscopy, Confocal; D010179:Pancreas / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D011796:Quinacrine; D013997:Time Factors
D011796:Quinacrine; D000109:Acetylcholine; D002118:Calcium