ABSTRACT
Ventricular fibrillation (VF) is a life-threatening arrhythmia, whose occurrence precedes the development of myocardial arrhythmogenic substrate resulting from either chronic or acute pathophysiological conditions. The authors' previous and current studies suggest that downregulated and/or heterogeneously distributed cell-to-cell coupling protein - connexin-43 (Cx43) - facilitates the development of malignant arrhythmias. It was hypothesized that VF itself deteriorates Cx43, and may hamper cardioversion into sinus rhythm. The purpose of the present study was to examine whether myocardial expression and the phosphorylated status of Cx43 is altered due to VF and during sinus rhythm restoration. Experiments were performed using 10-month-old male and female Wistar rats. Isolated Langendorff-mode-perfused rat hearts were subjected to the following events: basal condition, electrically induced VF lasting 2 min, electrically induced VF lasting 10 min, and sustained VF followed by spontaneous sinus rhythm restoration due to transient stop perfusion. The hearts were snap frozen at each event; ventricular tissue was sent for Cx43 immunoblotting using rabbit antiCx43 polyclonal antibody to detect phosphorylated (P-Cx43) as well as unphosphorylated (noP-Cx43) forms of Cx43, and mouse antiCx43 monoclonal antibody to detect noP-Cx43 only. Compared with basal conditions, total Cx43 expression did not change during experiments in either male or female rat hearts. However, P-Cx43 and the ratio of P-Cx43 to total Cx43 decreased significantly due to VF lasting 2 min and 10 min in male rat hearts only. In parallel, there was a significant increase in noP-Cx43 due to VF lasting 2 min and 10 min in male rat hearts only. Surprisingly, an enhancement of noP-Cx43 linked with suppression of P-Cx43 was detected during stop perfusion-induced termination of VF lasting 2 min, followed by sinus rhythm restoration in both male and female rat hearts. Sinus rhythm was not restored after 10 min of VF, which caused pronounced Cx43 dephosphorylation. In conclusion, there is a downregulation of Cx43 due to sustaining of VF, and it occurs earlier in male rat hearts compared with female rat hearts. It appears that transient no-flow-related inhibition of cell-to-cell coupling, as indicated by an increase in nonP-Cx43, can terminate VF followed by sinus rhythm restoration depending on the degree of previous Cx43 downregulation.
