Spatial organization of Ca(2+) entry and exocytosis in mouse pancreatic beta-cells.
Secretion from single pancreatic beta-cells was imaged using a novel technique in which Zn(2+), costored in secretory granules with insulin, was detected by confocal fluorescence microscopy as it was released from the cells. Using this technique, it was observed that secretion from beta-cells was limited to an active region that comprised approximately 50% of the cell perimeter. Using ratiometric imaging with indo-1, localized increases in intracellular Ca(2+) concentration ([Ca(2+)](i)) evoked by membrane depolarization were also observed. Using sequential measurements of secretion and [Ca(2+)](i) at single cells, colocalization of exocytotic release sites and Ca(2+) entry was observed when cells were stimulated by glucose or K(+). Treatment of cells with the Ca(2+) ionophore 4-Br-A23187 induced large Ca(2+) influx around the entire cell circumference. Despite the nonlocalized increase in [Ca(2+)](i), secretion evoked by 4-Br-A23187 was still localized to the same region as that evoked by secretagogues such as glucose. It is concluded that Ca(2+) channels activated by depolarization are localized to specific membrane domains where exocytotic release also occurs; however, localized secretion is not exclusively regulated by localized increases in [Ca(2+)](i), but instead involves spatial localization of other components of the exocytotic machinery.
Qian
W J
WJ
Department of Chemistry, University of Florida, Gainesville, Florida 32611-7200, USA.
Kennedy
R T
RT
D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism; D020013:Calcium Signaling; D002478:Cells, Cultured; D005089:Exocytosis; D005456:Fluorescent Dyes / Q000737:chemistry; D005947:Glucose / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007476:Ionophores / Q000494:pharmacology; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D008856:Microscopy, Fluorescence; D015363:Quinolones / Q000737:chemistry; D014105:Tosyl Compounds / Q000737:chemistry; D015032:Zinc / Q000378:metabolism
D015220:Calcium Channels; D005456:Fluorescent Dyes; D007328:Insulin; D007476:Ionophores; D015363:Quinolones; D014105:Tosyl Compounds; D000001:Calcimycin; D005947:Glucose; D015032:Zinc; C084731:zinquin