title: Ultrastructure of the myocardial cell and its membrane systems in the adult fly Calliphora erythrocephala (insecta: diptera).
abstract: Calliphora erythrocephala has cross-striated cardiac muscle cells with A, I and Z-bands. The diameters of the myosin and actin filaments are 200-250 A and 85 A respectively and the length of the myosin filaments (A-band) is approximately 1.5 micron. Usually 8-10 actin filaments surround each myosin filament. The myocardial cells show a well-developed membrane system and interior couplings. A perforated sheet of SR envelopes the myofibrils at the A-band, dilates into flattened cisternae at both A-I band levels before it merges into a three-dimensional net-work between the actin filaments of the I-bands and between the dense bodies of the discontinuous Z-discs. The T-system consists of broad flattened tubules running between the myofibrils at the A-I band levels forming dyads with the SR-cisternae. Longitudinal connections between the transverse (T-) tubules often occur. It is suggested that this well-developed SR may be an adaptation to facilitate a rapid contraction/relaxation frequency by an effective Ca2+ uptake.
mesh_terms: D000199:Actins; D000818:Animals; D004175:Diptera / Q000033:anatomy & histology*; D008566:Membranes; D008854:Microscopy, Electron; D009206:Myocardium / Q000648:ultrastructure*; D009210:Myofibrils; D009218:Myosins; D012519:Sarcoplasmic Reticulum
chemical_list: D000199:Actins; D009218:Myosins