Modulation by adrenaline of electrophysiological membrane parameters and contractility in intact and internally perfused single muscle fibres of the crayfish.

The effect of catecholamines on basic membrane characteristics (including labeled ionic fluxes) and contractile parameters was followed in current clamp and voltage clamp conditions in intact muscle fibres and internally perfused muscle fibre segments respectively of the crayfish Astacus fluviatilis; i.e. in muscle fibres which spike and activate tension on calcium principle.

Characterization of tension decline in different types of fatigue-resistant skeletal muscle fibres of the frog. Low extracellular calcium effects.

Twitch and tetanic tension have been measured in single skeletal muscle fibres (m.ileofibularis, Rana esculenta and Rana temporaria). On the basis of resistance to fatigue produced by repetitive tetanic stable frequency stimulation with various numbers of stimulation trains, twitch fibers were subdivided in three groups (resembling those as described by Westerblad and Lännergren 1986 in Xenopus), that is fatigue-resistant (FR), moderately fatigued (MF) and easily fatiguing (EF).

The effect of Pb2+ ions on calcium currents and contractility in single muscle fibres of the crayfish.

Muscle fibres of crustaceans represent an useful model for studying the mode of action of substances influencing calcium channels as the membrane generates the active responses on a pure calcium principle and the excitation-contraction link is dependent on external calcium. We followed the effect of Pb2+ ions (1-300 mumol/l) on contractile responses in single muscle fibres of the crayfish evoked by massive or intracellular electrical stimulation, by potassium depolarization and caffeine application, as well as on action potential in single intact muscle fibres and on calcium currents in voltage clamp conditions (vaseline gap) in internally perfused muscle fibre segments. All types of contractile responses, single twitches, tetanus, potassium and caffeine contractures were blocked.

Effects of ruthenium red on excitation and contraction in muscle fibres with Ca2+ electrogenesis.

The effect of ruthenium red (RR) on the electrical and contractile responses, membrane Ca currents, staining patterns of the external and internal membrane system were tested in intact and mechanically skinned muscle fibres of the crayfish Astacus fluviatilis. The following results were obtained: 1. Depression of the contractile responses following membrane depolarization (twitch, tetanus, potassium contractures).