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. The strontium action potential was blocked very effectively by Pb2+ ions. The total calcium currents which can be split by means of Hodgkin-Huxley equations into two components (fast and slow respectively) differing in the rate of activation and inactivation were suppressed after addition of Pb(NO3)2 (50-300 mumol/l). The effect of Pb2+ was concentration and time dependent. At lower concentrations (100 mumol/l) the blocking effect was more pronounced on the fast inactivating Ca current component. The Pb2+ ions prolonged the time constant of inactivation tau h of the slow channel, while leaving that of the fast channel intact.
Zacharová
D
D
Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, Bratislava.
Hencek
M
M
Pavelková
J
J
Lipská
E
E
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D003400:Astacoidea; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects*; D004553:Electric Conductivity; D007700:Kinetics; D007854:Lead / Q000494:pharmacology*; D008954:Models, Biological; D009119:Muscle Contraction / Q000187:drug effects; D009132:Muscles / Q000187:drug effects* / Q000378:metabolism
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D007854:Lead