Stephenson D G, Williams D A
J Muscle Res Cell Motil. 1980 Mar;1(1):73-87. doi: 10.1007/BF00711926.
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.
在不同浓度的Ca²⁺和Sr²⁺缓冲溶液中，对三种甲壳类动物（藤壶、小龙虾和螃蟹）和两种昆虫（蟑螂和蟋蟀）的机械去皮肤骨骼肌纤维进行激活，并测定其等长力响应。在所有甲壳类动物肌肉中，Sr²⁺诱导的最大力响应（P0Sr）仅为Ca²⁺诱导的最大力响应（P0Ca）的0 - 10%，但在昆虫中接近90%。对同时被Ca²⁺和Sr²⁺激活的藤壶肌肉纤维进行的实验表明，Sr²⁺与Ca²⁺竞争结合调节位点，但不能像Ca²⁺那样有效地将所有调节位点“开启”。有趣的是，在大多数完整十足目动物肌肉纤维中，动物解剖后4 - 6小时，以及在大多数藤壶肌肉纤维中解剖后24小时，P0Sr/P0Ca比值以及对Sr²⁺和Ca²⁺的敏感性都大幅增加。无论纤维的年龄如何，每种肌肉的Ca²⁺和Sr²⁺激活曲线的陡度相似，这意味着每种肌肉的激活过程涉及2个以上的Ca²⁺（2个Sr²⁺）。在所有研究的节肢动物肌肉纤维中都发现了具有生理重要性的Ca²⁺诱导Ca²⁺释放机制。
