TPA has no influence on the expression of myosin heavy chain isoforms in cultured adult cardiac muscle cells

Distribution and organization of desmin in cultured adult cardiac muscle cells: reflection on function

The cell-culture model for the study of desmin in adult cardiac muscle cells has provided insight into the function of desmin based on its distribution and structural organization. Initially, desmin emerged as a filamentous network from the existing amorphous form in the growing adult cardiac myocytes in vitro. Later, desmin became organized in various forms. In addition to the presence of a periodic array of desmin in the Z-line regions as observed in cardiac myocytes in vivo, longitudinally and transversely oriented strands of desmin were observed along the length of myofibrils in cardiac myocytes in vitro. These desmin strands and transverse perodicities formed a complex interwoven network, interlacing myofibrils of cells. Desmin and alpha-actinin were organized in ribbon- or aponeuroses-like structures that appeared as sheet-like, supportive structures for the cell body. The cellular cytoplasmic processes containing myofibrils were supported by desmin bars. The complex desmin network, desmin bars, transverse strands and ribbons or aponeuroses were observed in in vitro cardiac myocytes in contrast to in vivo cardiac myocytes. The functional implication of desmin, as indicated by in vivo studies, required more information concerning the organization of desmin for its supportive function, and is addressed in the present study. The elaborate organization of desmin provides evidence for its supportive function for the maintenance of the structural integrity and function of cardiac muscle cells.

Infection with the avian polyomavirus, BFDV, selectively affects myofibril structure in embryonic chick ventricle cardiomyocytes

Embryonic cardiomyocytes can both beat and divide. They assemble cardiac muscle-specific proteins into sarcomeric myofibrils and contract. In addition, they periodically synthesize DNA, complete mitosis, disassemble sarcomeric myofibrils in the area of the mitotic spindle, assemble cytoplasmic isoform-specific proteins into a cleavage furrow contractile ring, undergo cytokinesis, and then reform sarcomeric myofibrils in daughter cells. Little is known about how embryonic cardiomyocytes disassemble their myofibrils as they traverse the cell cycle and divide. In the present study, beating embryonic avian ventricular cardiomyocytes in primary culture were stimulated to initiate DNA synthesis without subsequent mitosis or cytokinesis by infection with the lytic avian polyomavirus, Budgerigar Fledgling Disease Virus (BFDV). Within 48 hours, infected, adherent cardiomyocytes disassemble most of their sarcomeric myofibrils, retaining cardiac myosin only in thin myofibrils with disrupted sarcomeric periodicity and in amorphous nonfibrillar pools. By 72 hours, infected cardiomyocytes contain no myofibrils and no longer react with antibodies to cardiac myosin. In contrast, infected cardiomyocytes continue to display cytoplasmic myosin localized in stress-fiber-like-structures in adherent cells, or in disrupted fibers and dispersed pools in detaching cells. Infected cardiomyocytes also continue to display interphase-like arrays of polymerized microtubules, even when rounded-up just prior to lysis. These results suggest that polyomavirus infection may provide a useful model system for further study of the regulation of myofibrils disassembly in embryonic cardiomyocytes.