Effects of CCK-8 on the cytoplasmic free calcium concentration in isolated rat islet cells

The C-terminal octapeptide of cholecystokinin (CCK-8) is known to stimulate insulin secretion. We examined its effects on the cytoplasmic free calcium concentration ([Ca 2+] IC) in isolated rat pancreatic islet cells. At 8.3 mM glucose and 1.28 mM Ca 2+, CCK-8 (100 nM) rapidly increased [Ca 2+] IC to a short-lived peak, whereafter the [Ca 2+] IC, within 1.5 minutes, fell to values below baseline. CCK-8 also rapidly increased the [Ca 2+] IC at 3.3 mM glucose and in a calcium deficient medium. However, either at low glucose or in the absence of extracellular Ca 2+, the post-peak [Ca 2+] IC did not fall below baseline levels. The CCK A receptor antagonist, L-364,718 (20 nM), inhibited the effects of CCK-8 on [Ca 2+] IC. The results suggest that CCK-8 in islet cells liberates calcium from intracellular stores by activating CCK A receptors.