Alterations in myocardial ultrastructure and protein expression after a single injection of isoproterenol.

Immunochemical and electron microscopic characterization of rat myocardium was conducted 2 h and 3 weeks after a single injection of isoproterenol in rats. The relative content of several myospecific proteins (KRP--kinase-related protein, desmin), cytoskeletal proteins (tubulin, vinculin, myosin light chain kinase--MLCK) and extracellular matrix protein fibronectin was determined by immunoblotting. Two hours after injection of 50 mg/kg isoproterenol a destruction of some cardiomyocytes, contracture of myofibrils and mild edema of intercellular space was observed. The content of all the studied proteins except KRP decreased below control levels. This situation sustained 3 weeks after injection and paralleled alterations in cardiomyocyte ultrastructure. Areas of myofibrillar contracture and lysis were noted, glycogen granules were sparse; mitochondria contained arrow-like inclusions that are characteristic for calcium overload, also huge mitochondria contacting each other by specialized intermitochondrial contacts were detected. Clumps of unripe elastic fibers in enlarged intercellular space were combined with increased deposition of collagens type I and III forming areas of fibrosis. The smaller dosage of isoproterenol (10 mg/kg) rendered no significant damage in the acute postinjection period but 3 weeks later it induced the thickening of extracellular matrix around cardiac cells and the increase in KRP and tubulin content by 26 and 32%, correspondingly. MLCK levels remained depressed throughout the experiment. The rise in KRP expression was also observed after the addition of isoproterenol to cultured chicken embryo cardiomyocytes. Obtained results indicate that even a single injection of isoproterenol creates long lasting structural alterations in cardiac muscle accompanied by the increased expression of extracellular matrix proteins and several sarcoplasmic proteins apparently involved in hypertrophic response of cardiomyocytes.

Alterations in myocardial cytoskeletal and regulatory protein expression following a single Doxorubicin injection.

Immunochemical and ultrastructural studies of the rat heart after a single injection of doxorubicin (2.2 or 0.44 mg/kg) were performed. Ventricles were taken for the study 2 h and 3 weeks after injection. The light and electron microscopy and immunohistochemical determination of collagens of I, III, and IV types and fibronectin using specific antibodies were implied. Quantitive immunoblotting was used to analyze the expression levels of cytoskeletal and extracellular matrix proteins such as desmin, tubulin, vinculin, fibronectin, kinase-related protein (KRP or telokin), and smooth muscle/nonmuscle myosin light-chain kinase (MLCK). Doxorubicin (2.2 mg/kg) did not influence the relative volume and structure of collagen network but distinctly reduced the density of fibronectin distribution and decreased the content of tubulin, fibronectin, MLCK, and KRP. After 3 weeks, an increased density and extension of collagen network were observed, indicating the development of diffuse fibrosis whereas the content of tubulin and KRP increased above control level by 50 +/- 2.3% and 20 +/- 5.2%, correspondingly. Similar but less pronounced alterations were observed following the administration of 0.44 mg/kg doxorubicin. The content of MLCK after both doses consistently remained about 30% below its level in untreated animals. Isolated chick embryo cardiomyocytes subjected to doxorubicin responded by a 26% increase in KRP expression 4 days after whereas the level of tubulin expression remained unchanged. Thus, the damage of myocardium after a single injection of a therapeutic dose of doxorubicin was followed by an increased expression of selected cytoskeletal and extracellular matrix proteins, suggesting their involvement in cardiac reparation.