Stanfield P R, Ashcroft F M
Can J Physiol Pharmacol. 1982 Apr;60(4):508-12. doi: 10.1139/y82-070.
Both vertebrate and invertebrate skeletal muscle fibres have Ca2+ permeability mechanisms which are turned on by depolarization of the surface membrane. In frog muscle, Ca currents are extremely slow and will be scarcely activated during the action potential that normally elicits a twitch. This Ca permeability cannot therefore play any substantial, direct role in excitation--contraction coupling. In insect (Carausius morosus) muscle, Ca currents activate within milliseconds of depolarization, even at low temperature, and may well play at least a triggering role in excitation--contraction coupling. These Ca currents show saturation with increasing [Ca]0, while the instantaneous current--voltage relation rectifies inwards, as expected from a very low [Ca]i. The Ca channel is permeable to Sr2+ and Ba2+. Inactivation of Ca currents under a maintained depolarization depends on Ca2+ carrying inward current, however, rather than on the depolarization itself.
脊椎动物和无脊椎动物的骨骼肌纤维都具有Ca2+通透性机制，该机制通过表面膜的去极化而开启。在青蛙肌肉中，Ca电流极其缓慢，在通常引发抽搐的动作电位期间几乎不会被激活。因此，这种Ca通透性在兴奋 - 收缩偶联中不能发挥任何实质性的直接作用。在昆虫（黄星蝗）肌肉中，即使在低温下，Ca电流在去极化的几毫秒内就会被激活，并且很可能在兴奋 - 收缩偶联中至少起到触发作用。这些Ca电流随着[Ca]0的增加而表现出饱和，而瞬时电流 - 电压关系向内整流，这与非常低的[Ca]i预期一致。Ca通道对Sr2+和Ba2+具有通透性。在持续去极化下Ca电流的失活取决于携带内向电流的Ca2+，而不是去极化本身。
