Differentiation between the Short and Long Term Effects of Glucose on the Intracellular Calcium Content of the Pancreaticβ-Cell*

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Abstract
The problem of how glucose affects the intracellular (La3+-nondisplaceable) Ca content of pancreatic .beta.-cells was approached by combining measurements of 45Ca in ob/ob-mouse islets loaded to isotopic equilibrium with determinations of Ca using electrothermal atomic absorption spectroscopy. Whereas short term changes of the glucose concentration induced marked alterations of insulin release, the islet content of intracellular 45Ca was remarkably stable. The chronic actions of glucose differed from the acute ones in being readily demonstrable and sometimes resulting even in a suppression of the Ca content. After 7 days of culture in 20 mM glucose, the amount of intracellular Ca was actually lower than when the islets were cultured at 5.5 mM glucose. The long term effect of glucose in suppressing the islet content of intracellular Ca was associated with degranulation and loss of immunoreactive insulin, indicated both from staining of the .beta.-cells and measurements of the extracted hormone by RIA [radioimmunoassay]. The previously unknown ability of glucose to suppress the islet content of intracellular Ca may consequently result from mobilization of the secretory granules.