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DOI: 10.1055/s-0032-1332592
Desipramine prevents from cardiac gap junction uncoupling
Objectives: Uncoupling of cardiac gap junction channels is an important arrhythmogenic mechanism in ventricular ischemia/reperfusion. Antiarrhythmic peptide AAP10 (H-Gly-Ala-Gly-Hyp-Pro-Tyr-CONH2) has been shown to prevent form acidosis-induced uncoupling and ischemia-related increase in dispersion. Previous structure-effect-investigations and subsequent computer modelling studies indicated that the tri-cyclic antidepressant desipramine mimicks certain sites of the binding region of AAP10 and, thus, may exert similar effects as AAP10.
Methods: First, we assessed binding of 14C-AAP10 to membranes of rabbit cardiac ventricles and its displacement with desipramine in a classical radioligand binding and competition study. Gap junction currents were measured between isolated pairs of human atrial cardiomyocytes under normal and acidotic (pH = 6.3) conditions with or without 1 µmol/l desipramine using dual whole cell voltage clamp. The effect of 1 µmol/l desipramine was assessed in isolated rabbit hearts (Langendorff-technique) undergoing local ischemia by coronary occlusion with 256 channel electrophysiological mapping and subsequent analysis of connexin43 expression, phosphorylation (Western blot) and sub-cellular localization (immunohistology).
Results: We found saturable 14C-AAP10-binding to cardiac membranes (KD: 0.29 ± 0.11 nmol/l; Bmax: 42.5 ± 7.2 pmol/mg) which could be displaced by desipramine with a KD.High= 0.14 µmol/l and a KD.Low= 22 µmol/l. Acidosis reduced gap junction conductance in human cardiomyocyte-pairs from 24.1 ± 4.7 to 11.5 ± 2.5 nS which could be significantly reversed by desipramine (26.6 ± 4.8 nS). In isolated hearts ischemia resulted in significantly increased dispersion of activation-recovery-intervals, loss of membrane connexin43, and de-phosphorylation of connexin43, which all could be prevented by desipramine.
Conclusions: Desipramine seems to prevent from uncoupling of cardiac gap junctions and from ischemia-related increase in dispersion. Although desipramine exerts a broad range of other effects, this opens the possibility to develop new more selective non-peptide ligands for targeting gap junctions.