CD38 disruption impairs glucose-induced increases in cyclic ADP-ribose, [Ca²⁺](i), and insulin secretion

Increases in [Ca²⁺](i) in pancreatic beta cells, resulting from Ca²⁺ mobilization from intracellular stores as well as Ca²⁺ influx from extracellular sources, are important in insulin secretion by glucose. Cyclic ADP-ribose (cADPR), accumulated in beta cells by glucose stimulation, has been postulated to serve as a second messenger for intracellular Ca²⁺ mobilization for insulin secretion, and CD38 is thought to be involved in the cADPR accumulation (Takasawa, S., Tohgo, A., Noguchi, N., Koguma, T., Nata, K., Sugimoto, T., Yonekura, H., and Okamoto, H. (1993) J. Biol. Chem. 268, 26052-26054). Here we created 'knockout' (CD38(-/-)) mice by homologous recombination. CD38(-/-) mice developed normally but showed no increase in their glucose-induced production of cADPR in pancreatic islets. The glucose- induced [Ca²⁺](i) rise and insulin secretion were both severely impaired in CD38(-/-) islets, whereas CD38(-/-) islets responded normally to the extracellular Ca²⁺ influx stimulants tolbutamide and KCl. CD38(-/-) mice showed impaired glucose tolerance, and the serum insulin level was lower than control, and these impaired phenotypes were rescued by beta cell-specific expression of CD38 cDNA. These results indicate that CD38 plays an essential role in intracellular Ca²⁺ mobilization by cADPR for insulin secretion.