Alignment Of Myofibrils Research Articles

Qualitative and quantitative observations on ultrastructural changes during postnatal development in the cat myocardium

Right ventricular papillary muscles obtained from neonatal ( s.d. ) in neonatal myocardium to 18.9±2.0 μm in the adult. T-tubules were not observed in neonatal cells, but could be seen in infant cells and formed 4.8±2.3% of total cell surface area in these preparations. T-tubules were prominent in adult myocardium and formed 17.3±3% of total cell surface area. The small cell size resulted in a significantly greater surface to volume ratio in neonatal (1.01±0.09 μm−1) than in adult (0.47±0.1 μm−1) myocardium. Evidence of active sarcomerogenesis was prominent in neonatal tissue but not in the adult. In addition, the alignment of myofibrils was less regular in neonatal myocardium than in adult or infant. Nexi or “gap junction” were observed in all muscles studied. In neonatal tissue, nexi formed 1.4±0.2% of cell surface area and in adult tissue, 3.4±0.1%. These results indicate that ultrastructural maturation continues during postnatal life in the cat myocardium.

Properties of isolated adult rat muscle fibres maintained in tissue culture.

1. Adult rat skeletal muscles were dissociated by collagenase treatment and trituration, and the isolated muscle fibres were maintained in vitro for 2-3 weeks. At various stages, the fibres were examined physiologically and morphologically. 2. The isolated fibres underwent some changes characteristic of muscle denervated in vivo. For instance, input resistance increased and extrajunctional acetylcholine (ACh) receptors appeared. In addition, the beginning stages of apparent muscle fibre fragmentation were observed. 3. In other respects, the cultured isolated fibres behaved differently than in vivo denervated fibres. Fibrillation developed only occasionally in vitro. The onset of ACh supersensitivity was slower (6 days) than after denervation in vivo (2-3 days). Some fibres developed localized regions of destriation, which apparently was due to loss of in-register alignment of myofibrils.