细胞外钙离子通过蟾蜍膀胱顶端阳离子通道控制外向整流：膜片钳和全膀胱研究

Extracellular Ca2+ controls outward rectification by apical cation channels in toad urinary bladder: patch-clamp and whole-bladder studies.

作者信息

Das S, Palmer L G

机构信息

Department of Physiology, Cornell University Medical College, New York, New York 10021.

出版信息

J Membr Biol. 1989 Feb;107(2):157-68. doi: 10.1007/BF01871721.

DOI:10.1007/BF01871721

PMID:2469799

Abstract

Outward rectifying, cation channels were observed in the epithelial cells of the urinary bladder of the toad. Bufo marinus. As studied in isolated cells using the patch-clamp technique, the channel has an average conductance of 24 and 157 pS for pipette potentials between 0 and +60 mV and -60 to -100 mV, respectively, when the major cation in both bath and pipette solutions is K+. The conductance of the channel decreases with increasing dehydration energy of the permeant monovalent cation in the order Rb+ = K+ greater than Na+ greater than Li+. Reversal potentials near zero under biionic conditions imply that the permeabilities for all four of these cations are similar. The channel is sensitive to quinidine sulfate but not to amiloride. It shares several pharmacological and biophysical properties with an outwardly-rectifying, vasopressin-sensitive apical K+ conductive pathway described previously for the toad urinary bladder. We demonstrate, in both single-channel and whole-bladder studies, that the outward rectification is a consequence of interaction of the channel with extracellular divalent cations, particularly Ca2+, which blocks inward but not outward current. Various divalent cations impart different degrees of outward rectification to the conductive pathway. Concentrations of Mg2+ and Ca2+ required for half-maximal effect are 3 X 10(-4) and 10(-4) M, respectively. For Co2+ the values are 10(-6) M at +50 mV and a 10(-4) M at +200 mV. The mechanism of blockade by divalent cations is not established, but does not seem to involve a voltage-dependent interaction in which the blocker penetrates the transmembrane electric field. In the absence of divalent cations in the mucosal solution, the magnitudes of inward current carried by Rb+, K+, Na+ and Li+ through the apical K+ pathway at any transepithelial voltage, are in the same order as in the single-channel studies. We propose that the cation channel observed by us in isolated epithelial cells is the single-channel correlate of the vasopressin-sensitive apical K+ conductive pathway in the toad urinary bladder and is also related to the oxytocin- and divalent cation-sensitive apical conductivity observed in frog skin and urinary bladder.

摘要

在海蟾蜍（Bufo marinus）膀胱上皮细胞中观察到外向整流阳离子通道。采用膜片钳技术在分离细胞中进行研究时，当浴液和微电极溶液中的主要阳离子均为K⁺时，对于0至 +60 mV和 -60至 -100 mV的微电极电位，该通道的平均电导分别为24和157 pS。通道的电导随着通透单价阳离子脱水能的增加而降低，顺序为Rb⁺ = K⁺＞Na⁺＞Li⁺。双离子条件下接近零的反转电位表明这四种阳离子的通透性相似。该通道对硫酸奎尼丁敏感，但对氨氯吡脒不敏感。它与先前描述的海蟾蜍膀胱外向整流、血管加压素敏感的顶端K⁺传导途径具有若干药理学和生物物理学特性。我们在单通道和全膀胱研究中均证明，外向整流是通道与细胞外二价阳离子（特别是Ca²⁺）相互作用的结果，Ca²⁺阻断内向电流但不阻断外向电流。各种二价阳离子对外向整流传导途径赋予不同程度的外向整流作用。半最大效应所需的Mg²⁺和Ca²⁺浓度分别为3×10⁻⁴和10⁻⁴ M。对于Co²⁺，在 +50 mV时为10⁻⁶ M，在 +200 mV时为10⁻⁴ M。二价阳离子的阻断机制尚未明确，但似乎不涉及阻滞剂穿透跨膜电场的电压依赖性相互作用。在黏膜溶液中不存在二价阳离子的情况下，在任何跨上皮电压下，Rb⁺、K⁺、Na⁺和Li⁺通过顶端K⁺途径携带的内向电流大小与单通道研究中的顺序相同。我们提出，我们在分离的上皮细胞中观察到的阳离子通道是海蟾蜍膀胱中血管加压素敏感的顶端K⁺传导途径的单通道对应物，并且还与蛙皮肤和膀胱中观察到的催产素和二价阳离子敏感的顶端导电性有关。