Gesztelyi I, Kathó J, Kövér A
Acta Physiol Hung. 1986;67(3):283-91.
On exposure (E) of frog semitendinosus muscle to 400 mmol/l urea (U) in sodium chloride Ringer's solution, the tension development to isoK+ solutions decreased, while in choline chloride Ringer it increased. On quick removal (R) of urea, always a block of excitation-contraction (E-C) coupling occurred accompanied by transient or persistent swelling of fibres and a similar but definite decrease of their resting membrane potential (Fig. 2). Muscle contraction could be elicited by caffeine even after UER-treatment but then only the slow tension increase (second phase of normal caffeine contraction) occurred (Fig. 3a). The fast tension increase to caffeine (first phase) could be restored if after UER-treatment 5 mmol/l mannitol (Fig. 3b), a 20 min treatment with choline chloride (Fig. 4a) or sodium isethionate (Fig. 4b) Ringer's solution of double osmolarity were applied. Caffeine contraction could not be elicited when sodium chloride Ringer's solution of double osmolarity was used under similar conditions (Fig. 5). E-C block to isoK+ solution persisted in all these experiments. E-C coupling could partially be restored by short treatment of muscle with caffeine (Figs 6a, b).
将青蛙半腱肌暴露于（E）含400 mmol/l尿素（U）的氯化钠林格氏液中时，对等钾溶液的张力发展降低，而在氯化胆碱林格氏液中则升高。快速去除（R）尿素后，总是会出现兴奋 - 收缩（E - C）偶联的阻断，同时伴有纤维的短暂或持续肿胀以及其静息膜电位的类似但明确的降低（图2）。即使在尿素去除后再给予咖啡因处理，肌肉仍可收缩，但此时仅出现缓慢的张力增加（正常咖啡因收缩的第二阶段）（图3a）。如果在尿素去除后再给予5 mmol/l甘露醇（图3b）、用双倍渗透压的氯化胆碱林格氏液（图4a）或羟乙基磺酸钠林格氏液（图4b）处理20分钟，则可恢复对咖啡因的快速张力增加（第一阶段）。在类似条件下使用双倍渗透压的氯化钠林格氏液时，无法引发咖啡因收缩（图5）。在所有这些实验中，对等钾溶液的E - C阻断持续存在。用咖啡因对肌肉进行短时间处理可部分恢复E - C偶联（图6a、b）。
