Cyclic AMP activates multiple signal pathways, crucial for the pancreatic -cells cell's function and survival, and is a major potentiator of insulin release. A family of PDEs terminate the cyclic AMP signals. We examined the expression of PDEs in rat -cells and their role in the regulation of insulin response. Using RT-PCR and Western blot analyses, we identified PDE3A, PDE3B, PDE4B, PDE4D and PDE8B in rat islets and in INS-1E cells, and several possible splice variants of these PDEs. Specific depletion of PDE3A with siRNA (siPDE3A) led to a small (67%) increase in the insulin response to glucose in INS-1E cells but not in rat islets. siPDE3A had no effect on the GLP-1 (10 nmol/l) potentiated insulin response in rat islets. Depletion in PDE8B levels in rat islets using similar technology (siPDE8B) increased insulin response to glucose by 70%, the potentiation being of similar magnitude during 1^st and 2^nd phase insulin release. The siPDE8B –potentiated insulin response was further increased by 23% when GLP-1 was included during the glucose stimulus. PDE8B is expressed in a small number of tissues unrelated to glucose or fat metabolism. We propose that PDE8B, an IBMX-insensitive cyclic AMP-specific phosphodiesterase, could prove a novel target for enhanced insulin response, affecting a specific pool of cyclic AMP involved in the control of insulin granule trafficking and exocytosis. Finally, we discuss evidence for functional compartmentation of cyclic AMP in pancreatic -cells.