title: Activation of skinned arthropod muscle fibres by Ca2+ and Sr2+.
abstract: Mechanically skinned skeletal muscle fibres of three crustaceans (barnacle, crayfish and crab) and two insects (cockroach and cricket) were activated in Ca2+- and Sr2+-buffered solutions of different concentrations and the isometric force response was determined. The maximum force response induced by Sr2+ (P0Sr) was only 0-10% of that induced by Ca2+ (P0Ca) in all crustacean muscles, but approached 90% in insects. Experiments on barnacle muscle fibres activated simultaneously by Ca2+ and Sr2+ suggested that Sr2+ competes with Ca2+ for binding onto the regulatory sites without, however, being able to turn all of them 'on' as efficiently as Ca2+. Interestingly, the ratio P0Sr/P0Ca and the sensitivity for both Sr2+ and Ca2+ increased substantially after 4-6 h following the dissection of the animals in most intact decapod muscle fibres and after 24 h in most barnacle muscle fibres. The steepness of the activation curves for both Ca2+ and Sr2+ was similar for each muscle regardless of the age of the fibre and implied that more than 2 Ca2+ (2 Sr2+) were involved in the activation process of each muscle. A Ca2+-induced Ca2+ release mechanism of physiological importance was found to operate in all arthropod muscle fibres investigated.
mesh_terms: D000818:Animals; D001181:Arthropods / Q000502:physiology*; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D003445:Crustacea / Q000502:physiology; D007313:Insecta / Q000502:physiology; D009119:Muscle Contraction / Q000187:drug effects*; D009132:Muscles / Q000502:physiology*; D013324:Strontium / Q000494:pharmacology*
chemical_list: D002118:Calcium; D013324:Strontium