Inhibitory effect of CCK-8 and ceruletide on glutamate-induced rises in intracellular free calcium concentrations in rat neuron cultures

Abstract To study the mechanism by which cholecystokinin octapeptide (CCK-8) and its potent analogue, ceruletide, prevent glutamate-induced neuronal cell death in rat neuron cultures, we examined the effect of both peptides on glutamate-induced increases in the intracellular free calcium concentrations ([Ca 2+ ] i ), which are known to be a crucial trigger of the neurodegeneration induced by glutamate. CCK-8 itself did not alter [Ca 2+ ] i in rat neuron cultures. Glutamate increased [Ca 2+ ] i in neuron cultures rapidly and markedly. CCK-8 and ceruletide significantly suppressed the increases in [Ca 2+ ] i induced by glutamate. The maximum inhibitory effects of CCK-8 and ceruletide at 10 −6 M reached 43 and 46% of the response to glutamate, respectively. Gastrin-I and CCK-4 also significantly attenuated the increases in [Ca 2+ ] i induced by glutamate. The inhibitory effect of CCK-8 was completely blocked by the selective antagonist for CCK-B receptors, (+)L-365,260, but not by (−)L-364,718, which is a selective antagonist for CCK-A receptors. CCK-8 significantly suppressed [Ca 2+ ] i response to kainate and high concentrations of extracellular K + , but not to N- methyl- d -aspartate . With cultured astrocytes, CCK-8 did not inhibit the increment of [Ca 2+ ] i induced by glutamate. These findings clearly demonstrated that CCK-8 and ceruletide inhibit glutamate-induced increases in [Ca 2+ ] i in neuron cultures through CCK-B receptors, suggesting that CCK-8 may participate in the central actions of glutamate.