Inositol 1,4,5-trisphosphate (IP3) increased the free-Ca2+ concentration in the incubation medium of permeabilized ob/ob mouse pancreatic islets. Spermine decreased the free-Ca2+ concentration through stimulation of mitochondrial Ca2+ uptake and attenuated the effect of IP3. Mg2+ antagonized the effects of spermine, thereby increasing the free-Ca2+ concentration and enhancing the effect of IP3 on the free-Ca2+ concentration. Because IP3 releases Ca2+ from endoplasmic reticulum, these results indicate that endoplasmic reticulum and mitochondria can interact in the regulation of the free-Ca2+ concentration in the cytosol of the pancreatic β-cell.

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