Protein kinase Calpha mediates the effect of antiarrhythmic peptide on gap junction conductance

We investigated the effects of the antiarrhythmic peptide AAP10 (GAG-4Hyp-PY-CONH2, 50 nM) on pairs of adult guinea pig cardiomyocytes and on pairs of HeLa-cells transfected with rat connexin43 (Cx43). Using double cell voltage clamp technique in cardiomyocytes under control conditions, gap junction conductance (Gj) steadily decreased (by -0.3 to -0.4 nS/min). In contrast, 50 nM AAP10 significantly enhanced Gj (by +0.22 to +0.29 nS/min). This effect of AAP10 could be significantly antagonized by bisindolylmaleimide I (BIM), and by the protein kinase C (PKC) subtype-specific inhibitors HBDDE (PKCgamma and -alpha) and CGP 54345 (PKCalpha). In HeLa-Cx43 cells we found similar electrophysiological effects of AAP10. For further analysis, we incubated HeLa-Cx43 cells with [32P]orthophosphate (0.05 mCi/ml) for 4 h at 37 degrees C followed by addition of 50 nM AAP10 for 15 min. We found that incorporation of 32P into Cx43 was significantly enhanced in the presence of AAP10, which was completely inhibited in presence of BIM. PKC enzyme-linked immunosorbent assay (ELISA) revealed significant activation of PKC by AAP10 in HeLa-Cx43 cells, which could be inhibited by HBDDE and CGP 54345. Finally, a binding study using [14C]-AAP10 as radioligand was performed. We found a saturable binding of [14C]-AAP10 with a KD of 0.88 nM to cardiac membrane preparations. For assessment of the antiarrhythmic activity in anesthetized rats, we infused aconitine until the occurrence of ventricular fibrillation (VF). The aconitine dose required for initiation of VF was significantly enhanced in the presence of AAP10. In conclusion; AAP10 increases Gj in both adult cardiomyocytes and transfected HeLa-Cx43 cells. AAP10 leads to enhanced phosphorylation of Cx43 via activation of PKCalpha. A membrane receptor exists for antiarrhythmic peptides.