Rotigaptide Revisited: New Insights into the Molecular Mechanisms of Gap Junction Agonism

It’s been decades since the synthetic version of an atrial anti-arrhythmic peptide AAP10 and its D-isomer rotigaptide were developed and demonstrated to increase myocardial gap junction conductance (g _j ). This increase in cardiomyocyte electrical communication was linked to PKC activation by ELISA assays, PKC activation by phorbol esters, or attenuation by biochemical inhibitors of PKCa. Studies in connexin43, -45, or -40 transfected cell lines further demonstrated that the effects of these gap junction agonists on cardiac g _j were predominantly due to gating effects on Cx43, with some on Cx45, and little or no effect on Cx40 gap junctions. Since Cx43 is known to be regulated by phosphorylation and ³² P was demonstrated to be incorporated into Cx43 by AAP10, the prevailing hypothesis has been that these gap junction agonists alter the gating of Cx43 gap junctions by PKC-dependent phosphorylation mechanisms. However, there are conflicting reports of PKC-downregulation of Cx43 gap junction communication and the carboxyl tail domain of Cx43 is known to contain at least 19 phosphorylation sites associated with no less than six different protein kinases. Preliminary studies in primary neonatal mouse ventricular myocyte (NMVM) cultures demonstrate that PKA and JNK inhibition prevents the acute increase in gap junction conductance (g _j ) in NMVM cell pairs. JNK inhibition or 100 nM rotigaptide treatment both attenuated the 90% decline in NMVM g _j observed during perfusion with 10% normal glucose (0.1 g/L) saline solution. Together, these new preliminary observations suggest the involvement of a PKA-dependent JNK inhibitory signaling pathway in the enhancement of cardiac g _j by rotigaptide.