Heterogeneous Loss of Connexin43 Protein in Ischemic Dog Hearts

INTRODUCTION: Ischemia causes cell decoupling in the myocardium. Prolonged ischemia activates proteases and causes degradation of structural proteins as well as gap junctions. There is little information about the degradation of gap junction protein during the early time period after acute ischemia. The purpose of the present study was to investigate connexin43 (Cx43) protein degradation and distribution patterns in the canine left ventricular wall during 1 to 6 hours of ischemia. METHODS AND RESULTS: Ischemia of canine left ventricular myocardium was induced by ligation of the left anterior descending coronary artery. Following a period of in situ ischemia of up to 6 hours, samples were harvested, and standard paraffin slides were prepared for Cx43 and wheat germ agglutinin double labeling. Cx43 distribution was visualized by confocal microscopy. In controls, homogeneous distribution of Cx43 staining was determined. Ischemia caused a loss of Cx43 with a heterogeneous pattern by mixing foci of infarcted cells among normal cardiac myocytes. To determine if the changes were induced by heterogeneous reduction in the blood supply, an in vitro ischemic model was studied to induce more homogeneous ischemia. Western blot analysis of these in vitro ischemic tissue samples revealed a reduction of Cx43 protein concentration with a 50% decay time of 4.8 hours. Cx43 dephosphorylation was detected after 1 hour of in vitro ischemia. Heterogeneous loss of Cx43 was found in the in vitro ischemic tissue. There were no significant changes in Cx43 staining density during the first hour of ischemia at a time when dephosphorylation of the protein was observed. After 1 hour of ischemia, Cx43 was reduced at intercalated disk areas, and, after 6 hours, most Cx43 disappeared at intercalated disk areas, while small amounts of Cx43 remained at side-to-side junctions. CONCLUSION: Cx43 undergoes both distribution and concentration changes following acute cardiac ischemia. The loss of Cx43 protein is heterogeneous. Cx43 dephosphorylation occurred within 1 hour following ischemia.