Dephosphorylation and intracellular redistribution of ventricular connexin43 during electrical uncoupling induced by ischemia

Electrical uncoupling at gap junctions during acute myocardial ischemia con tributes to conduction abnormalities and reentrant arrhythmias. Increased l evels of intracellular Ca2+ and H+ and accumulation of amphipathic lipid me tabolites 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 jun ction protein, connexin43 (Cx43). Adult rat hearts perfused on a Langendorf f apparatus were subjected to ischemia or ischemia/reperfusion. Changes in coupling were monitored by measuring whole-tissue resistance. Changes in th e amount and distribution of phosphorylated and nonphosphorylated isoforms of Cx43 were measured by immunoblotting and confocal immunofluorescence mic roscopy using isoform-specific antibodies. In control hearts, virtually all Cx43 identified immunohistochemically at apparent intercellular junctions was phosphorylated. During ischemia, however, Cx43 underwent progressive de phosphorylation with a time course similar to that of electrical uncoupling , The total amount of Cx43 did not change, but progressive reduction in tot al Cx43 immunofluorescent signal and concomitant accumulation of nonphospho rylated Cx43 signal occurred at sites of intercellular junctions. Functiona l recovery during reperfusion was associated with increased levels of phosp horylated Cx43. These observations suggest that uncoupling induced by ische mia is associated with dephosphorylation of Cx43, accumulation of nonphosph orylated Cx43 within gap junctions, and translocation of Cx43 from gap junc tions into intracellular pools.