Enhanced Functional Gap Junction Neoformation by Protein Kinase A–Dependent and Epac-Dependent Signals Downstream of cAMP in Cardiac Myocytes

Abstract

Gap junctions (GJs) constituted by neighboring cardiac myocytes are essential for gating ions and small molecules to coordinate cardiac contractions. cAMP is suggested to be a potent stimulus for enhancement of GJ function. However, it remains elusive how cAMP potentiates the GJ of cardiomyocytes. Here we demonstrated that the gating function of GJ is enhanced by the protein kinase A (PKA)–dependent signal, and that the accumulation of connexin43 (Cx43), the most abundant Cx in myocytes, is enhanced by an exchange protein directly activated by cAMP (Epac) (Rap1 activator)–dependent signal. The gating function of GJs was analyzed by microinjected dye transfer method. The accumulation of Cx43 was analyzed by quantitative immunostaining. Using the PKA-specific activator N6-benzoyladenosine-3′,5′-cyclic monophosphate (6Bnz) and Epac-specific activator 8-(4-chlorophenylthio)-2′-O-methyladenosine-3′,5′-cyclic monophosphate (8CPT), we could delineate the two important downstream signals of cAMP for enhanced GJ n...