Previously, it was shown that antiarrhythmic peptides and our lead substance AAP10 enhance electrical intercellular communication via gap junctions. Now, we wanted to elucidate whether AAP10 acts preferably in the ischemic area and the molecular mechanism of this peptide. Seventeen rabbit hearts were isolated, perfused according to Langendorff, and submitted to 30-min local ischemia by LAD occlusion with/without AAP10 (50 nM). Electrophysiology was assessed by 256 channel epicardial mapping. Finally, the ischemic zone, border zone, and non-ischemic zone were excised, and the cardiac gap junction protein connexin43 (Cx43), its phosphorylation state, and the distribution at the polar and lateral membrane of cardiomyocytes were determined by Western blot and immunofluorescence. Ischemia led to a decrease in activation recovery interval (ARI) homogeneity, which could be completely prevented by AAP10. Moreover, ischemia-induced activation wave slowing in the ischemic border zone was antagonized by AAP10. In ischemic center and border zone, but not in the non-ischemic area, (phospho-Cx43/dephospho-Cx43)-ratio decreased. This was also significantly antagonized by AAP10. Serine 368 was identified as one phosphorylation site for the activity of AAP10. In the non-ischemic area, AAP10 had no influence on Cx43 phosphorylation state. Interestingly, ischemia led to a loss of Cx43 from the cell poles and lateral sides in the ischemic area and border zone. AAP10 completely prevented the ischemia-induced decrease in polar Cx43 presence. In the ischemic area, AAP10 prevents from ischemia-induced Cx43 dephosphorylation and loss of Cx43 from the gap junction at cell poles and in parallel prevents the decrease in ARI homogeneity and attenuates ischemia-induced slowing of activation wave propagation. The AAP10 action seems confined to the ischemic area.

Co-ordinated electrical activation of the heart is maintained by intercellular coupling of cardiomyocytes via gap junctional channels located in the intercalated disks. These channels consist of two hexameric hemichannels, docked to each other, provided by either of the adjacent cells. Thus, a complete gap junction channel is made from 12 protein subunits, the connexins. While 21 isoforms of connexins are presently known, cardiomyocytes typically are coupled by Cx43 (most abundant), Cx40 or Cx45. Some years ago, antiarrhythmic peptides were discovered and synthesised, which were shown to increase macroscopic gap junction conductance (electrical coupling) and enhance dye transfer (metabolic coupling). The lead substance of these peptides is AAP10 (H-Gly-Ala-Gly-Hyp-Pro-Tyr-CONH(2)), a peptide with a horseshoe-like spatial structure as became evident from two-dimensional nuclear magnetic resonance studies. A stable D: -amino-acid derivative of AAP10, rotigaptide, as well as a non-peptide analogue, gap-134, has been developed in recent years. Antiarrhythmic peptides act on Cx43 and Cx45 gap junctions but not on Cx40 channels. AAP10 has been shown to enhance intercellular communication in rat, rabbit and human cardiomyocytes. Antiarrhythmic peptides are effective against ventricular tachyarrhythmias, such as late ischaemic (type IB) ventricular fibrillation, CaCl(2) or aconitine-induced arrhythmia. Interestingly, the effect of antiarrhythmic peptides is higher in partially uncoupled cells and was shown to be related to maintained Cx43 phosphorylation, while arrhythmogenic conditions like ischaemia result in Cx43 dephosphorylation and intercellular decoupling. It is still a matter of debate whether these drugs also act against atrial fibrillation. The present review outlines the development of this group of peptides and derivatives, their mode of action and molecular mechanisms, and discusses their possible therapeutic potential.

Coordinated electrical activation of the heart is essential for the maintenance of a regular cardiac rhythm and effective contractions. Action potentials spread from one cell to the next via gap junction channels. Because of the elongated shape of cardiomyocytes, longitudinal resistivity is lower than transverse resistivity causing electrical anisotropy. Moreover, non-uniformity is created by clustering of gap junction channels at cell poles and by non-excitable structures such as collagenous strands, vessels or fibroblasts. Structural changes in cardiac disease often affect passive electrical properties by increasing non-uniformity and altering anisotropy. This disturbs normal electrical impulse propagation and is, consequently, a substrate for arrhythmia. However, to investigate how these structural changes lead to arrhythmias remains a challenge. One important mechanism, which may both cause and prevent arrhythmia, is the mismatch between current sources and sinks. Propagation of the electrical impulse requires a sufficient source of depolarizing current. In the case of a mismatch, the activated tissue (source) is not able to deliver enough depolarizing current to trigger an action potential in the non-activated tissue (sink). This eventually leads to conduction block. It has been suggested that in this situation a balanced geometrical distribution of gap junctions and reduced gap junction conductance may allow successful propagation. In contrast, source-sink mismatch can prevent spontaneous arrhythmogenic activity in a small number of cells from spreading over the ventricle, especially if gap junction conductance is enhanced. Beside gap junctions, cell geometry and non-cellular structures strongly modulate arrhythmogenic mechanisms. The present review elucidates these and other implications of passive electrical properties for cardiac rhythm and arrhythmogenesis.