COMPARISON OF THE EFFECTS OF POTASSIUM AND MEMBRANE-POTENTIAL ON THE CALCIUM-DEPENDENT SODIUM-EFFLUX IN SQUID AXONS
COMPARISON OF THE EFFECTS OF POTASSIUM AND MEMBRANE-POTENTIAL ON THE CALCIUM-DEPENDENT SODIUM-EFFLUX IN SQUID AXONS
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DOI：
10.1113/jphysiol.1986.sp016207
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发表时间：
1986-09-01
影响因子：
5.5
通讯作者：
BAKER, PF
中科院分区：
文献类型：
--
作者：
ALLEN, TJA;BAKER, PF
1.实验中描述的[Ca] o-依赖的组件22 Na流出的膜电位控制电压钳的条件下进行监测。2.外排系统对外部Ca的表观亲和力在胆碱海水中非常低（表观KD apprx. 50 mM）;但当胆碱被Li或K等渗替代时显著增加（表观KD apprx. 1-2 mM）。Ca内流以平行方式变化。三羟甲基氨基甲烷的作用与胆碱很相似，而胍的作用约为锂的三分之二。3.用K替代Li对外部Ca的表观亲和力几乎没有影响，但最大通量略有增加（30-40%）。最大通量的增加可以通过施加K之前的电位的电超极化来去除，并且在不存在K的情况下，可以通过电去极化来模仿。这些实验表明，钾对钙依赖的钠外流到锂海水的刺激作用是电的起源。4.部分胆碱被钾替代刺激钙依赖性钠外流，但只有部分这种刺激可以通过电超极化和，在K的情况下，电去极化只带来了一个相对较小的刺激。这是因为在胆碱海沃茨中加入钾后，只有一部分刺激是电性的：其余部分反映了钾的化学作用引起的对外部钙的表观亲和力的增加。K的最大外排量比胆碱的最大外排量高约40%。这可能反映了电效应，这一点得到了以下观察结果的支持：电去极化增加了进入含110 mM-Ca的胆碱海水的通量，其中Ca结合位点接近饱和。5.采用电压钳技术测定了锂海水、胆碱海水和含100 mM-Na的胆碱海水中Ca依赖性Na流出的电压依赖性。在所有三种情况下，流量随着去极化而增加，并且在+70 mV时仍在上升。对电位的依赖性不是很陡，在约50 mV时出现e倍增加。
1. Experiments are described in which the [Ca]o-dependent component of 22Na efflux is monitored under conditions of membrane potential control by voltage clamp. 2. The apparent affinity of the efflux system for external Ca is very low in choline sea water (apparent KD .apprx. 50 mM); but increases dramatically when choline is replaced isosmotically by Li or K (apparent KD .apprx. 1-2 mM). Ca influx changes in a parallel fashion. Tris behaves much like choline and guanidinium is about two-thirds as effective as Li. 3. Replacement of Li by K has little effect on the apparent affinity for external Ca but brings about a small (30-40%) increase in the maximal flux. The increase in maximum flux can be removed by electrical hyperpolarization to the potential before application of K and, in the absence of K, can be mimicked by electrical depolarization. These experiments suggest that the stimulatory effect of K on the Ca-dependent Na efflux into Li sea water is electrical in origin. 4. Partial replacement of choline by K stimulates the Ca-dependent Na efflux; but only part of this stimulation can be removed by electrical hyperpolarization and, in the absence of K, electrical depolarization only brings about a relatively small stimulation. This is because only part of the stimulation that follows addition of K to choline sea waters is electrical in origin: the rest reflects an increase in the apparent affinity for external Ca that is brought about by K acting chemically. The maximum efflux into K is about 40% higher than that into choline. That this may reflect an electrical effect is supported by the observation that electrical depolarization increases the flux into choline sea water containing 110 mM-Ca where the Ca-binding site is close to saturation. 5. The voltage clamp was used to determine the voltage dependence of the Ca-dependent Na efflux into Li sea water, choline sea water and choline sea water containing 100 mM-Na. In all three cases the flux increased with depolarization and was still rising at + 70 mV. The dependence on potential was not very steep, an e-fold increase occurred over approximately 50 mV.