Reperfusion after brief ischemia disrupts the microtubule network in canine hearts

Histological changes in the stunned myocardium are believed to be minimal. This study examined whether cytoskeletal structures of microtubules are disrupted in the stunned myocardium. In 38 dogs, the left anterior descending coronary artery was occluded for 15 minutes and reperfused to produce the stunned myocardium. Microtubules were stained immunohistochemically. In intact myocardium, microtubules appeared as a filamentous network throughout the cytoplasm and encircled the nucleus. This pattern was not affected by 15 minutes of ischemia. One hour of reperfusion, however, disrupted microtubular structure substantially (disruption score in the endocardium, 53.4 +/- 6.0%) although actin filaments remained intact. Microtubular structures were reconstituted 1-3 days after reperfusion, showing supernormal immunoreactivity. Five days after reperfusion, the pattern of microtubular staining was normal. In another protocol, the role of Ca2+ during reperfusion in microtubular disruption was examined. When intracoronary infusion of EDTA (1.67 mumol/kg body wt per minute) was performed during the initial 10 minutes of reperfusion, myocardial stunning was attenuated. The fractional shortening in the perfused area after 1 hour of reperfusion was 20.1 +/- 1.2% versus 11.5 +/- 0.5% in the control condition (p < 0.05), and the microtubular disruption score was lower (12.6 +/- 1.4%). Although intracoronary infusion of calcium chloride (9 mumol/kg body wt per minute) for 10 minutes in nonischemic hearts increased contractile function (fractional shortening, 25.3 +/- 2.0%), it severely disrupted microtubular networks (microtubular disruption score, 64.0 +/- 10.6%). We conclude that microtubules supporting the structural integrity of myofibrils and other organelles are reversibly disrupted by reperfusion after brief ischemia probably through calcium overload.