VIDEO IMAGE-ANALYSIS OF LABILE ZINC IN VIABLE PANCREATIC-ISLET CELLS USING A SPECIFIC FLUORESCENT-PROBE FOR ZINC

We used an intracellular zinc-specific fluorophore, Zinquin, in conjun ction with fluorescence video image analysis, to reveal labile zinc in pancreatic islet cells, which concentrate this metal for use in synth esis, storage, and secretion of insulin. Zinquin vividly demonstrated zinc in the islet cell secretory granules, which formed a brightly lab eled crescent in the cytoplasm between one side of the nucleus and the plasma membrane. Lower but still appreciable amounts of zinc were det ected in the remaining cytoplasm, but there was little labeling in the nucleus. Fluorescence intensity varied among islet cells, suggesting differences in zinc content. Their average fluorescence intensity grea tly surpassed that of the surrounding pancreatic acinar cells in froze n sections of pancreas and in all other types of cell studied, includi ng lymphocytes, neutrophils, fibroblasts, and erythrocytes. Less labil e zinc was detected in cells of the mouse insulinoma cell line NIT-1, regardless of whether they were maintained in long-term culture in the presence or absence of exogenous extracellular zinc. Exposure of isle t or insulinoma cells to a high concentration of glucose or other secr etagogue decreased the content of labile zinc. Zinquin should be a use ful probe for revealing changes in zinc homeostasis in islet B-cells t hat may be important in their dysfunction and death during diabetes.