Frank G B, Treffers R C
Jpn J Physiol. 1977;27(2):215-24. doi: 10.2170/jjphysiol.27.215.
Exposing frog's toe muscles to Ringer's solution made hypertonic with 400 mM urea for 60 min followed by placing the muscles back in Ringer's (urea-removal treatment) completely blocks the twitch without disrupting the surface openings of the T-tubules. The urea-removal treatment also increased the triadic junction width. Placing the muscles in Ringer's with an elevated calcium concentration (5 mM) following exposure to the hyertonic solution prevented the block of the twitch response but not the increase in the triadic junction width. Exposing untreated muscles to Ringer's with 5 mM calcium either had no effect on the twitch on reduced it by 30 percent or less. These results suggest the possibility that increasing the width of the triadic junction decreases the amount of calcium ions reaching the terminal cisternae during an action potential thereby blocking the twitch. Elevating the calcium concentration in the T-tubules would increase the amount of calcium which enters the triadic junction during an action potential and thus antagonize the above effects.
将青蛙的趾肌暴露于用400 mM尿素制成的高渗林格氏液中60分钟，然后将肌肉放回林格氏液中（去除尿素处理），完全阻断了肌肉收缩，同时不破坏T小管的表面开口。去除尿素处理还增加了三联体连接宽度。在暴露于高渗溶液后，将肌肉置于钙浓度升高（5 mM）的林格氏液中可防止肌肉收缩反应的阻断，但不能防止三联体连接宽度的增加。将未处理的肌肉暴露于含5 mM钙的林格氏液中，要么对肌肉收缩没有影响，要么使其降低30%或更少。这些结果表明，增加三联体连接宽度可能会减少动作电位期间到达终末池的钙离子数量，从而阻断肌肉收缩。提高T小管中的钙浓度会增加动作电位期间进入三联体连接的钙量，从而对抗上述作用。
