[Slow asymmetric currents and ultrastructure of tubulo-reticular contacts in the muscle fibers of the crayfish].

Asymmetric membrane currents were studied in isolated muscle fibres of the crayfish Astacus fluviatilis under conditions of voltage clamp and controlled composition of both the external and internal environment. In addition to fast asymmetric currents, probably associated with the opening of calcium channels in the superficial membrane, slow asymmetric currents could be also observed in this type of muscle fibre; the time course of the latter currents was almost by one order slower than that of the fast muscle fibres of the frog. The value of the displaced charge was related to the number of feet in the tubulo-reticular (TR) junction. The number of feet and their distribution in the TR junction were studied using transmission electron microscopy. The amount of charges displaced per one foot supports the hypothesis stating that slow displacements currents are associated with displacement of charged particles distributed over the entire area of sarcolemmal and tubular invaginations rather than in the feet alone.