[Slow asymmetric currents and ultrastructure of tubulo-reticular contacts in the muscle fibers of the crayfish]. / Medlennye asimmetrichnye toki i ul'trastruktura tubulo-retikuliarnykh kontaktov v myshechnykh voloknakh raka.

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.

[Ionic conductivity of muscle fiber membranes of Locusta migratoria]. / Ionnaia provodimost' membrany myshechnykh volokon saranchi Locusta migratoria.

On muscle fibers from m. flexor tibiae of the locust studies have been made of the effect of rapid changes in potassium and chloride concentrations on the membrane potential (MP). The MP constituted 56.0 +/- 1.0 mV. The relationship between the MP and the external potassium at [K]o.[Cl]o equals const may be described by Nernst equation for two different intracellular concentrations of these ions, at [K]o less than or equal to 40 mM and at [K]o greater than or equal to 80 mM. From the relationship between the MP and rapid changes in [K]o or [Cl]o at constant concentration of correspondingly [Cl]o and K]o relative membrane conductivity for these ions were found (TK=0.55 and TC1=0.41). Using impulse analysis, electrical constants of muscle membrane were determined (lambda = 1.9 +/- 0.1 mm; Ri equals 103 +/- 7 ohm.cm; Rm = 1.430 +/- 76 ohm.cm2; Cm = 16 +/- 1 muF.cm-2). High values for Cm correlate with numerous invaginations in muscle membrane which were revealed in electron microscopis investigations. Active responses of the membrane are gradual. In the presence of ions of Sr they are transformed into regenerative action potentials.