[Excitation-contraction coupling in isolated muscle fibers with calcium electrogenesis preserved in a culture medium]. / Väzba excitácie a kontrakcie v izolovaných svalových vláknach s kalciovou elektrogenézou prechovávaných v kultivacnom médiu.

The aim of the present work was to check changes in functional characteristics of isolated muscle cells, operating on the calcium electrogenesis principle, while kept in culture media for several days. Skeletal muscle cells of the crayfish Astacus fluviatilis were used to study potassium/caffeine contractures and single/tetanic contractions; simultaneous electrical and mechanical responses were recorded by the microelectrode technique, and kinetics of calcium ionic currents was studied under vaseline-gap voltage clamp. In cultured fibers, active membrane responses and calcium current kinetics remained unchanged, or slightly increased, whereas contractile responses were substantially reduced. A gradual excitation-contraction decoupling was observed. The fiber maintained the ability to respond to direct activation (by caffeine) of the contractile apparatus. Subthreshold caffeine concentrations (0.2-0.5 mmol/l) and adrenaline (6.0(-6), 6.10(-5) mol/l) enhanced the inhibited (due to the culturing) single contractile responses.

The roles of haemocytes during degeneration and regeneration of crayfish muscle fibres.

Crayfish haemolymph contains three types of haemocytes with cytoplasmic granules: coagulocytes, granulocytes and amoebocytes. Muscle degeneration was induced by either a gross mechanical injury or a mild puncture injury of m. extensor carpopoditi. Granulocytes and amoebocytes were involved in the phagocytosis of disintegrating muscle fibres. Within three weeks after the gross injury the first myotubes were found. The formation of regenerated fibres started before the degenerating material was removed completely. Mild injury resulted in the formation of contraction clots, localized at the ends of a fibre and connected to a persistent external lamina in the form of an empty sheath. The external lamina sheaths were invaded by amoebocytes. They arranged themselves into a superficial layer similar to an epithelium, formed gap junctions and zonulae adherentes, and showed an increase in the number of cytoplasmic microtubules. These transformed haemocytes retained their ability to engulf material of the disintegrating fibre. In about three weeks the number of microtubules in the transformed haemocytes decreased, and newly formed contractile filaments appeared. Satellite cells are present along the normal crayfish muscle fibres. Following their activation in degenerated material, they might conceivably induce the transformation of haemocytes into myogenic cells.