Refinements in the short-circuit technique and its application to active potassium transport across the cecropia midgut.
Refinements in the short-circuit technique and its application to active potassium transport across the cecropia midgut.
复制标题
短路技术的改进及其在天蚕中肠主动钾转运中的应用。
DOI：
--
复制
发表时间：
1978
影响因子：
2.8
通讯作者：
R. Moreton
中科院分区：
文献类型：
--
作者：
J. Wood;R. Moreton
1.用于测量跨上皮的电势差的常规双电极方法由于浴介质中的电流流动引起的电势梯度而受到误差。数学分析表明，测量短路电流的误差与浴槽介质的电阻率和两记录电极的间距成正比。对于介质电阻率高而组织电阻率低的昆虫幼虫中肠，这一现象尤为严重。2.已经设计了一种系统，其使用第三记录电极来直接监测浴介质中的电位梯度。通过适当的电连接，可以自动补偿梯度，留下残余误差，该残余误差取决于组织的厚度，但不取决于电极间隔。因为大多数上皮细胞的厚度小于最小实际电极间距，所以该误差小于双电极系统中固有的误差。3.由于电压梯度是自动补偿的，因此可以获得连续的电位和电流读数。描述了一种“电压钳”电路，它允许研究短路电流的时间过程。4.用三电极系统研究了盲杯蛾幼虫的中肠。五个实验的平均结果为：初始电位差（开路）：98+/-11 mV（S.E.M.）; 60分钟时短路电流：498+/-160微安cm=2; 60分钟时的“稳态”电阻：150+/-26 Ω cm 2。电流相当于18.6 μ-当量cm-2 h-1的净钾运输。5.中肠的电参数随时间迅速变化。电位差衰减的半衰期约为158 min，电阻增加的半衰期约为16 min，短路电流衰减的两个指数项之和，半衰期分别约为16和158 min。此外，电位和短路电流显示阶跃变化的瞬态响应。6.中肠的属性进行了比较与其他运输上皮细胞，并讨论了它们的依赖程度的折叠的准备。他们的时间依赖性的背景下，钾含量的组织中的变化进行了讨论，并根据一个稳定状态的假设的测量的影响进行了概述。
1. The conventional, two-electrode method for measuring potential difference across an epithelium is subject to error due to potential gradients caused by current flow in the bathing medium. Mathematical analysis shows that the error in measuring short-circuit current is proportional to the resistivity of the bathing medium and to the separation of the two recording electrodes. It is particularly serious for the insect larval midgut, where the resistivity of the medium is high, and that of the tissue is low. 2. A system has been devised, which uses a third recording electrode to monitor directly the potential gradient in the bathing medium. By suitable electrical connexions, the gradient can be automatically compensated, leaving a residual error which depends on the thickness of the tissue, but not on the electrode separation. Because the thicknesses of most epithelia are smaller than the smallest practical electrode spacing, this error is smaller than that inherent in a two-electrode system. 3. Since voltage-gradients are automatically compensated, it is possible to obtain continuous readings of potential and current. A 'voltage-clamp' circuit is described, which allows the time-course of the short-circuit current to be studied. 4.The three-electrode system has been used to study the larval midgut of Hyalophora cecropia. The average results from five experiments were: initial potential difference (open-circuit): 98+/-11 mV (S.E.M.); short-circuit current at time 60 min: 498+/-160 microA cm=2; 'steady-state' resistance at 60 min: 150+/-26 omega cm2. The current is equivalent to a net potassium transport of 18.6 mu-equiv cm-2 h-1. 5. The electrical parameters of the midgut change rapidly with time. The potential difference decays with a half-time of about 158 min, the resistance increases with a half-time of about 16 min, and the short-circuit current decays as the sum of two exponential terms, with half-times of about 16 and 158 min respectively. In addition, potential and short-circuit current show transient responses to step changes. 6. The properties of the midgut are compared with those of other transporting epithelia, and their dependence on the degree of folding of the preparation is discussed. Their time-dependence is discussed in the context of changes in potassium content of the tissue, and the implications for measurements depending on the assumption of a steady state are outlined.