Evidence for the involvement of cAMP-GEF (Epac) pathway in amylase release from the rat parotid gland

Amylase release from the rat parotid gland is mainly mediated in a cAMP-dependent protein kinase (PKA)-dependent manner. In the present study, amylase release mediated in cAMP-dependent and PKA-independent manners was investigated with a cAMP-regulated guanine nucleotide exchange factor (cAMP-GEF: Epac)-selective cAMP analogue, 8CPT-2Me-cAMP. The Epac was localized in the intracellular and the plasma membrane fractions. PKA activation by 8CPT-2Me-cAMP was 100-fold lower than that by cAMP. The amylase release (% of the total) from the intact parotid acinar cells was 16 and 3.6% by isoproterenol (1 μM) and 8CPT-2Me-cAMP (200 μM), respectively, and that from the saponin-permeabilized cells was 15 and 3% by cAMP (100 μM) and 8CTP-2Me-cAMP (10 μM), respectively. H-89 inhibited cAMP-induced amylase release, but did not inhibit 8CPT-2Me-cAMP-induced amylase release. These results indicated that amylase release by β-adrenergic stimulation is mediated through both the cAMP/PKA and cAMP/Epac signal pathways.