Picher M, Decrouy A, Rousseau E
Department of Physiology and Biophysics, Faculty of Medicine, University of Sherbrooke, Canada.
Biochim Biophys Acta. 1996 Feb 21;1279(1):93-103. doi: 10.1016/0005-2736(95)00239-1.
Sarcoplasmic reticulum (SR) K+ channels from canine diaphragm were studied upon fusion of longitudinal and junctional membrane vesicles into planar lipid bilayers (PLB). The large-conductance cation selective channel (gamma(max) = 250 pS; Km = 33 mM) displays long-lasting open events which are much more frequent at positive than at negative voltages. A major subconducting state about 45% of the fully-open state current amplitude was occasionally observed at all voltages. The voltage-dependence of the open probability displays a sigmoid relationship that was fitted by the Boltzmann equation and expressed in terms of thermodynamic parameters, namely the free energy (delta Gi) and the effective gating charge (Zs): delta Gi = 0.27 kcal/mol and Zs = -1.19 in 250 mM potassium gluconate (K-gluconate). Kinetic analyses also confirmed the voltage-dependent gating behavior of this channel, and indicate the implication of at least two open and three closed states. The diaphragm SR K+ channel shares several biophysical properties with the cardiac isoform: g = 180 pS, delta Gi = 0.75 kcal/mol, Zs = -1.45 in 150 mM K-gluconate, and a similar sigmoid P(o)/voltage relationship. Little is known about the regulation of the diaphragm and cardiac SR K+ channels. The conductance and gating of these channels were not influenced by physiological concentrations of Ca2+ (0.1 microM-1 mM) or Mg2+ (0.25-1 mM), as well as by cGMP (25-100 microM), lemakalim (1-100 microM), glyburide (up to 10 microM) or charybdotoxin (45-200 nM), added either to the cis or to the trans chamber. The apparent lack of biochemical or pharmacological modulation of these channels implies that they are not related to any of the well characterized surface membrane K+ channels. On the other hand, their voltage sensitivity strongly suggests that their activity could be modulated by putative changes in SR membrane potential that might occur during calcium fluxes.
在将犬膈肌的纵行膜囊泡和连接膜囊泡融合到平面脂双层（PLB）中后，对其肌浆网（SR）钾通道进行了研究。大电导阳离子选择性通道（γ(max)=250 pS；Km = 33 mM）表现出持久的开放事件，在正电压下比在负电压下更为频繁。在所有电压下偶尔会观察到一种主要的亚导通状态，其电流幅度约为完全开放状态电流幅度的45%。开放概率的电压依赖性呈现出一种S形关系，可用玻尔兹曼方程拟合，并以热力学参数表示，即自由能（ΔGi）和有效门控电荷（Zs）：在250 mM葡萄糖酸钾（K-葡萄糖酸钾）中，ΔGi = 0.27 kcal/mol，Zs = -1.19。动力学分析也证实了该通道的电压依赖性门控行为，并表明至少涉及两个开放状态和三个关闭状态。膈肌SR钾通道与心脏异构体具有若干生物物理特性：在150 mM K-葡萄糖酸钾中，g = 180 pS，ΔGi = 0.75 kcal/mol，Zs = -1.45，且具有相似的S形P(o)/电压关系。关于膈肌和心脏SR钾通道的调节知之甚少。这些通道的电导和门控不受生理浓度的Ca2+（0.1 μM - 1 mM）或Mg2+（0.25 - 1 mM）影响，也不受添加到顺式或反式腔室中的cGMP（25 - 100 μM）、雷马卡林（1 - 100 μM）、格列本脲（高达10 μM）或蝎毒素（45 - 200 nM）影响。这些通道明显缺乏生化或药理学调节，这意味着它们与任何已充分表征的表面膜钾通道均无关联。另一方面，它们的电压敏感性强烈表明，其活性可能会受到钙通量期间可能发生的SR膜电位假定变化的调节。
