Planar lipid bilayr and patch clamp studies on the single channel currents of cardiac sarcop lasmic reticulum.

本文用平面脂双层技术研究了低浓度(PCa 7.5~3)细胞内钙离子对犬心肌肌浆网单一钾通道的影响。EGTA与氯化钙混合后可获得较低的浓度。通过改变细胞质表面的主成分分析在3到7.5之间，观察到两个新的效应。首先，随着细胞内Ca~(2+)浓度的增加，开放状态的单位电流幅度增大；在此浓度下，电压-电流关系为欧姆关系。第二，Ca~(2+)浓度的增加增加了开放的概率。钙离子的这两种作用都是剂量依赖的，并且在所有被测试的通道中都被一致地观察到。因此，所观察到的肌浆网钾通道属于钙激活钾通道的一类。第二条钙离子对犬心脏肉瘤…单个钾通道电流的调制作用用平面脂质双层技术研究了更多的弹性网状结构。随着Ca~(2+)浓度从PCA_3降低到PCA_(7.5)，开态几率和单位开态电流都逐渐减小。每条单通道I-V曲线在任何PCA处都是欧姆的：在此范围内，Ca~(2+)和Gt~(2+)的调制作用与电压无关。在所用电压下，通道两侧的电导和开放概率的剂量-效应曲线均为双相曲线。然而，在所使用的PCA范围内，钙离子在细胞质一侧引起的电导和门控特性的激活明显比在SR管腔一侧更显著。此外，当细胞质中的钙离子浓度大于Pca 3时，电导下降。这种情况下的I-V关系表现为电压依赖的快速阻断引起的内向整流。这提示心肌SR K~+通道电流可能通过通道上和通道内不同类型的Ca~(2+)&gt~(2+)结合部位被激活或抑制。较少

Article 1 The effects of low (pCa 7.5 to 3) concentrations of intracellular calcium ion on a single potassium channel in the sarcoplasmic reticulum of canine heart ventricular muscle were investigated using a planar lipid bilayr technique. The low concentrations were obtained by mixing EGTA and calcium chloride. By varying the pCa of the cytoplasmic face between 3 to 7.5, two novel effects were observed. First, an increase in the intracellular Ca^<2+> concentration produced an increase in the unit current amplitude of open states ; the voltage-current relationship was ohmic at these concentrations. Second, an increase in the Ca^<2+> concentration increased the open probability. Both these effects of Ca^<2+> were dose-dependent, and were consistently observed in all channels tested. Thus, the SR potassium channel observed appears to belong to the class of Ca^<2+>-activated potassium channels.Article2 The modulating effects of Ca^<2+> on single K^+ channel currents in canine heart sarcop … More lasmic reticulum were studied using a planar lipid bilayr technique. The open-state probability and the unitary open-state current both decreased gradually as the Ca^<2+> concentration was reduced from pCa 3 to pCa 7.5. Each single-channel I-V curve was ohmic at any pCa : the modulating effect of Ca^<2+> within this range was voltage independent. The Ca^<2+> dose-response curves for the conductances and open probabilities were all biphasic in shape for both sides of the channel at the voltages used. However, Ca^<2+> within the pCa ranges used caused significantly more prominent activation of conductance and gating properties on the cytoplasmic side than it did on the SR luminal side. Furthermore, conductance decreased when cytoplasmic Ca^<2+> concentrations were greater than pCa 3. The I-V relation in this instance exhibited inward rectification caused by a voltage-dependent fast block. This suggests than cardiac SR K^+ channel currents may be activated or inhibited through various types Ca^<2+> binding sites on and within the channels. Less