Striated myocytes and atrial specific granules in the pulmonary veins of chronically infarcted rat hearts

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Abstract
Summary The ultrastructure of the striated myocytes in the pulmonary myocardium of the Wistar rat, was studied following left ventricular infarction (LVI) for 4 days and 4 weeks, respectively. Ischemia was provided by ligating of the left coronary artery which successively produces left ventricular dysfunction and congestion of the left atrium and pulmonary veins. In general, the striated myocytes of the extrapulmonary veins of the control groups displayed ultrastructural characteristics similar to those of the left atrium. However, in the former, transverse tubules commonly occurred making interior couplings with the SR at the I-band levels. Also, between striated myocytes of the intrapulmonary veins of the controls nexus-like junctions of about 2 µm length were observed. Further, in the same groups atrial specific granules (ASG), including A-granules and B-granules, were present in about 20%–30% of the striated myocytes of the extrapulmonary veins as shown in single sections. The ASG tended to decrease by number in areas approaching the lung hilus and were not observed in the intrapulmonary veins of the controls. After 4 days of ventricular ischemia granules also appeared in the intrapulmonary veins. They were mostly seen in single and randomly spread in the cytoplasm of a limited number of cells, i.e., in between 0% and 5% of the myocytes as seen in single sections. Four days of LVI produced only minor cellular injuries to the extrapulmonary and intrapulmonary venous wall, while more severe lesions appeared in both areas following 4 weeks of LVI. Such lesions were preferably localized to the adluminal surface and consisted mainly of Z-band and sarcomere anomalies, vacuolization of the cytoplasm and mitochondrial swelling.