蛙类去表皮骨骼肌纤维中肌浆网原位钾通道的生理作用及选择性
Physiological role and selectivity of the in situ potassium channel of the sarcoplasmic reticulum in skinned frog skeletal muscle fibers.
作者信息
Abramcheck C W, Best P M
机构信息
Department of Physiology and Biophysics, University of Illinois, Urbana 61801.
出版信息
J Gen Physiol. 1989 Jan;93(1):1-21. doi: 10.1085/jgp.93.1.1.
The role of K+ as a counterion during Ca2+ release from the sarcoplasmic reticulum (SR) has been investigated. An optical technique using the Ca2+-sensitive dye antipyrylazo III monitored Ca2+ release from skinned (sarcolemma removed) muscle fibers of the frog. Skinned fibers were used since the removal of the sarcolemma allows direct access to the SR membrane. Releases were stimulated by caffeine, which activates Ca2+ release directly by binding to a receptor on the SR. Two different methods were used to decrease the SR K+ conductance so that its effect on Ca2+ release could be assessed: (a) the SR K+ channel blocker, 1,10-bis-quanidino-n-decane (bisG10) was used to eliminate current pathways and (b) substitution of the impermeant ion choline for K+ was used to decrease charge carriers. Both bisG10 and choline substitution caused a concentration-dependent decrease in the Ca2+ release rate. Therefore we conclude that K+ is an important counterion for Ca2+ during its release from the SR. The selectivity of the in situ SR K+ channel to several monovalent cations was determined by substituting them for K+ and comparing their effect on Ca2+ release. The substituted ions were expected to affect Ca2+ release in proportion to their ability to support a counterion flux, which is, in turn, a function of their relative conductance through the SR K+ channel. The selectivity sequence determined by these experiments was K+ = Rb+ = Na+ greater than Cs+ greater than Li+ greater than choline.
钾离子（K⁺）在肌浆网（SR）释放钙离子（Ca²⁺）过程中作为抗衡离子的作用已得到研究。采用一种光学技术，利用对Ca²⁺敏感的染料安替比拉宗III监测青蛙去膜（去除肌膜）肌纤维中Ca²⁺的释放。之所以使用去膜纤维，是因为去除肌膜后可直接接触到SR膜。通过咖啡因刺激释放，咖啡因通过与SR上的受体结合直接激活Ca²⁺释放。采用两种不同方法降低SR的K⁺电导率，以便评估其对Ca²⁺释放的影响：（a）使用SR K⁺通道阻滞剂1,10 - 双胍基 - n - 癸烷（bisG10）消除电流通路，（b）用不透膜的离子胆碱替代K⁺以减少电荷载体。bisG10和胆碱替代均导致Ca²⁺释放速率呈浓度依赖性降低。因此我们得出结论，K⁺在Ca²⁺从SR释放过程中是重要的抗衡离子。通过用几种单价阳离子替代K⁺并比较它们对Ca²⁺释放的影响，确定了原位SR K⁺通道对这些阳离子的选择性。预期替代离子对Ca²⁺释放的影响与其支持抗衡离子通量的能力成比例，而抗衡离子通量又是它们通过SR K⁺通道的相对电导率的函数。通过这些实验确定的选择性顺序为K⁺ = Rb⁺ = Na⁺＞Cs⁺＞Li⁺＞胆碱。
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