Electrical uncoupling at gap junctions during acute myocardial ischemia contributes to conduction abnormalities and reentrant arrhythmias. Increased levels of intracellular Ca(2+) and H(+) and accumulation of amphipathic lipid metabolites during ischemia promote uncoupling, but other mechanisms may play a role. We tested the hypothesis that uncoupling induced by acute ischemia is associated with changes in phosphorylation of the major cardiac gap junction protein, connexin43 (Cx43). Adult rat hearts perfused on a Langendorff apparatus were subjected to ischemia or ischemia/reperfusion. Changes in coupling were monitored by measuring whole-tissue resistance. Changes in the amount and distribution of phosphorylated and nonphosphorylated isoforms of Cx43 were measured by immunoblotting and confocal immunofluorescence microscopy using isoform-specific antibodies. In control hearts, virtually all Cx43 identified immunohistochemically at apparent intercellular junctions was phosphorylated. During ischemia, however, Cx43 underwent progressive dephosphorylation with a time course similar to that of electrical uncoupling. The total amount of Cx43 did not change, but progressive reduction in total Cx43 immunofluorescent signal and concomitant accumulation of nonphosphorylated Cx43 signal occurred at sites of intercellular junctions. Functional recovery during reperfusion was associated with increased levels of phosphorylated Cx43. These observations suggest that uncoupling induced by ischemia is associated with dephosphorylation of Cx43, accumulation of nonphosphorylated Cx43 within gap junctions, and translocation of Cx43 from gap junctions into intracellular pools.

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Rationale: Transmural dispersion of repolarization has been shown to play a role in the genesis of ventricular tachycardia and fibrillation in different animal models of heart failure (HF). Heterogeneous changes of repolarization within the midmyocardial population of ventricular cells have been considered an important contributor to the HF phenotype. However, there is limited electrophysiological data from the human heart. Objective: To study electrophysiological remodeling of transmural repolarization in the failing and nonfailing human hearts. Methods and Results: We optically mapped the action potential duration (APD) in the coronary-perfused scar-free posterior-lateral left ventricular free wall wedge preparations from failing (n‫)5؍‬ and nonfailing (n‫)5؍‬ human hearts. During slow pacing (S1S1‫0002؍‬ ms), in the nonfailing hearts we observed significant transmural APD gradient: subepicardial, midmyocardial, and subendocardial APD80 were 383؎21, 455؎20, and 494؎22 ms, respectively. In 60% of nonfailing hearts (3 of 5), we found midmyocardial islands of cells that presented a distinctly long APD (537؎40 ms) and a steep local APD gradient (27؎7 ms/mm) compared with the neighboring myocardium. HF resulted in prolongation of APD80: 477؎22 ms, 495؎29 ms, and 506؎35 ms for the subepi-, mid-, and subendocardium, respectively, while reducing transmural APD80 difference from 111؎13 to 29؎6 ms (P<0.005) and presence of any prominent local APD gradient. In HF, immunostaining revealed a significant reduction of connexin43 expression on the subepicardium. Conclusions: We present for the first time direct experimental evidence of a transmural APD gradient in the human heart. HF results in the heterogeneous prolongation of APD, which significantly reduces the transmural and local APD gradients. (Circ Res. 2010;106:981-991.)Key Words: heart failure Ⅲ repolarization Ⅲ transmural gradient Ⅲ optical mapping Ⅲ connexin43 H eart failure (HF) claims more than 200 000 lives annually in the US alone. 1,2 Approximately a half of these deaths are sudden and presumably caused by ventricular tachyarrhythmias. Pathophysiological remodeling of cardiac function occurs at multiple levels and includes the alterations in a host of ion channels, Ca 2ϩ -handling proteins, and proteins mediating cell-cell coupling, predisposing to arrhythmias and sudden death. 3 Numerous animal models have shown the importance of such electrophysiological (EP) remodeling in the mechanisms of HF-related arrhythmogenesis. 4 Prolongation of the repolarization is a hallmark of cells and tissues isolated from failing hearts independent of the cause, which has been observed in isolated myocytes 5 and intact ventricular preparations. 4,6 This fundamental change in myocyte biology underlies QT-interval prolongation of the surface ECG in patients with HF. The action potential (AP) prolongation is heterogeneous, resulting in exaggeration of the physiological heterogeneity of electric properties in the failing heart. 1,4 These cellular EP changes were linked to down...