蟾蜍皮肤中卤化物通量的浓度依赖性及阴离子通道的选择性

Concentration dependence of halide fluxes and selectivity of the anion pathway in toad skin.

作者信息

Harck A F, Larsen E H

出版信息

Acta Physiol Scand. 1986 Oct;128(2):289-304. doi: 10.1111/j.1748-1716.1986.tb07977.x.

DOI:10.1111/j.1748-1716.1986.tb07977.x

Abstract

The isolated toad (Bufo bufo) skin was mounted under voltage-clamp conditions in a chamber shown to cause no significant edge damage. The serosal side of the skin was bathed with NaCl-Ringer's, and the passive voltage-sensitive anion conductance studied in its fully voltage activated state, V = -80 mV (apical bath negative). The active sodium currents were eliminated by replacing external Na+ with K+. With [Cl-]o varying between 1.45 mM and 110 mM (gluconate substitution) and [I-]o = 3 mM, the total clamping current (y) and the sum of halide currents (x), estimated from flux measurements, were related by y = 1.0x-3.7 microA cm-2 (r2 = 0.98, n = 50 preparations). The increase in [Cl-]o produced a sigmoidal increase in Cl- influx and clamping current, with the rate coefficient for the influx increasing with [Cl-]o for 1.45 less than [Cl-]o less than 60 mM, but decreasing slightly again as [Cl-]o was further raised to 110 mM. A similar relationship was obtained between the rate coefficient for the Br- influx and [Br-]o, and the I- influx and [Cl-]o, indicating that these three ions are transported by a pathway that is activated by Cl-o and Br-o. The rate coefficients for the influxes ranked as follows, I-:Cl-:Br- = 0.7:1:1.3. The I-/Cl- selectivity was shown to be independent of the degree of Cl-o activation of the anion pathway, and identical with the I-/Cl- selectivity of a furosemide-sensitive, conductive pathway. With [Cl-]o, [Br-]o, or [I-]o = 110 mM, the currents ranked as follows, Cl-:Br-:I- = 1:0.68:0.06, indicating that Cl-, to a lesser extent Br-, and I-, poorly activate the conductive anion pathway. External I- was a potent inhibitor of the Cl-o activation of the Cl- conductance. The unidirectional I- fluxes ([I-]o = [I-]i = 3 mM, [Cl-]o = [Cl-]i = 110 mM) revealed passive transport for V less than -50 mV, active transport for V = o mV, and exchange diffusion for V = 50 mV, confirming our previous finding that depending on the transepithelial potential, the toad skin exhibits three modes of anion transport. A model that shares some properties with that of the anion transport system of the red cell membrane accounts for our findings, and for an inwardly directed active Cl- flux in terms of Cl-/HCO3- exchange.

摘要

将分离的蟾蜍（Bufo bufo）皮肤置于电压钳制条件下，置于一个经测试不会造成明显边缘损伤的腔室中。皮肤的浆膜侧用NaCl - 林格氏液灌注，在其完全电压激活状态（V = -80 mV，顶端浴液为负）下研究被动电压敏感阴离子电导。通过用K⁺替代外部Na⁺消除活性钠电流。当[Cl⁻]ₒ在1.45 mM和110 mM之间变化（葡萄糖酸盐替代）且[I⁻]ₒ = 3 mM时，根据通量测量估计的总钳制电流（y）和卤化物电流之和（x）的关系为y = 1.0x - 3.7 μA cm⁻²（r² = 0.98，n = 50个标本）。[Cl⁻]ₒ的增加导致Cl⁻内流和钳制电流呈S形增加，对于1.45 mM ＜ [Cl⁻]ₒ ＜ 60 mM，内流的速率系数随[Cl⁻]ₒ增加，但当[Cl⁻]ₒ进一步升高到110 mM时又略有下降。在Br⁻内流的速率系数与[Br⁻]ₒ之间以及I⁻内流与[Cl⁻]ₒ之间获得了类似的关系，表明这三种离子通过由Cl⁻ₒ和Br⁻ₒ激活的途径进行转运。内流的速率系数排序如下，I⁻:Cl⁻:Br⁻ = 0.7:1:1.3。I⁻/Cl⁻选择性被证明与阴离子途径的Cl⁻ₒ激活程度无关，并且与速尿敏感的导电途径的I⁻/Cl⁻选择性相同。当[Cl⁻]ₒ、[Br⁻]ₒ或[I⁻]ₒ = 110 mM时，电流排序如下，Cl⁻:Br⁻:I⁻ = 1:0.68:0.06，表明Cl⁻在较小程度上Br⁻以及I⁻对导电阴离子途径的激活较差。外部I⁻是Cl⁻电导的Cl⁻ₒ激活的有效抑制剂。单向I⁻通量（[I⁻]ₒ = [I⁻]ᵢ = 3 mM，[Cl⁻]ₒ = [Cl⁻]ᵢ = 110 mM）显示对于V ＜ -50 mV为被动转运，对于V = 0 mV为主动转运，对于V = 50 mV为交换扩散，证实了我们之前的发现，即根据跨上皮电位，蟾蜍皮肤表现出三种阴离子转运模式。一个与红细胞膜阴离子转运系统具有一些共同特性的模型解释了我们的发现，以及根据Cl⁻/HCO₃⁻交换向内的活性Cl⁻通量。