Allen T J, Baker P F
J Physiol. 1986 Sep;378:77-96. doi: 10.1113/jphysiol.1986.sp016208.
Experiments are described in which Ca efflux is monitored in axons under voltage clamp. As Ca efflux consists of more than one component, conditions were sought where one component predominates. Thus external Na-dependent Ca efflux can be studied in relative isolation either at pH 9.0 or in fully poisoned axons immersed in Ca-free media; external Ca-dependent Ca efflux can be studied in fully poisoned axons immersed in Na-free media and the Na-independent, energy requiring, pump is best examined in Na and Ca-free sea waters. Both in unpoisoned axons at pH 9.0 and fully poisoned axons at pH 7.8, the external Na-dependent Ca efflux is activated by hyperpolarization and inhibited by depolarization. Depolarizations achieved either electrically or by exposure to high K are roughly comparable and the inhibition brought about by high K can largely be removed by electrical hyperpolarization to the initial resting potential. In both Na sea waters and choline sea waters containing 100 mM-Na, Ca efflux is increased e-fold over approximately 50 mV. In choline sea water, external Ca-dependent Ca efflux from fully poisoned axons is unaffected by voltage over the range -80 to -30 mV. But addition of K or Li activates the flux and this activation is increased by hyperpolarization and decreased by depolarization, suggesting that the activating cation may also be transported into the axon. The Na-independent, energy-requiring, flux is inhibited by electrical hyperpolarization and stimulated by electrical depolarization. External K also stimulates the flux and part of this stimulation can be removed by electrical hyperpolarization. These data show that the energy-dependent pump is sensitive to membrane potential in the physiological range and suggest that it may be an electrogenic process. The finding that voltage affects the energy-dependent (uncoupled) pump and external Na-dependent fluxes in opposite directions may help explain why the total Ca efflux from intact axons responds to potential in a very variable manner.
本文描述了在电压钳制下监测轴突中钙外流的实验。由于钙外流由多个成分组成，因此需要寻找一种成分占主导的条件。因此，可以在pH 9.0的环境中或在浸泡于无钙培养基中的完全中毒轴突中相对独立地研究外部钠依赖性钙外流；可以在浸泡于无钠培养基中的完全中毒轴突中研究外部钙依赖性钙外流，而在无钠和无钙的海水中可以最好地检测不依赖钠、需要能量的泵。在pH 9.0的未中毒轴突和pH 7.8的完全中毒轴突中，外部钠依赖性钙外流均由超极化激活，由去极化抑制。通过电刺激或暴露于高钾实现的去极化大致相当，高钾引起的抑制作用在很大程度上可通过电超极化恢复到初始静息电位而消除。在含有100 mM钠的钠海水和胆碱海水中，钙外流在约50 mV范围内增加了e倍。在胆碱海水中，完全中毒轴突的外部钙依赖性钙外流在-80至-30 mV范围内不受电压影响。但是添加钾或锂会激活通量，这种激活通过超极化增加，通过去极化减少，这表明激活阳离子也可能被转运到轴突中。不依赖钠、需要能量的通量受到电超极化的抑制，受到电去极化的刺激。外部钾也刺激通量，这种刺激的一部分可通过电超极化消除。这些数据表明，能量依赖性泵在生理范围内对膜电位敏感，并表明这可能是一个生电过程。电压以相反方向影响能量依赖性（解偶联）泵和外部钠依赖性通量这一发现，可能有助于解释为什么完整轴突的总钙外流对电位的反应方式非常多变。
