8-CPT-2Me-cAMP sodium is a selective activator of exchange proteins activated by cAMP (Epac) , the cAMP sensitive guanine nucleotide exchange factors (GEFs) for the small GTPases Rap1 and Rap2. 8-CPT-2Me-cAMP sodium activates Epac1 ( EC 50 = 2.2 μM), but not PKA ( EC 50 > 10 μM). 8-CPT-2Me-cAMP sodium stimulates Epac-mediated Ca 2+ release in pancreatic β-cells in vitro.