THE POSITIVE AND NEGATIVE HEAT PRODUCTION ASSOCIATED WITH A NERVE IMPULSE
THE POSITIVE AND NEGATIVE HEAT PRODUCTION ASSOCIATED WITH A NERVE IMPULSE
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DOI：
10.1098/rspb.1958.0012
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发表时间：
1958-01-01
期刊：
影响因子：
--
通讯作者：
HOWARTH, JV
中科院分区：
文献类型：
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作者：
ABBOTT, BC;HILL, AV;HOWARTH, JV
用比以前更快的记录设备重新研究了无髓神经（Mala）的“初始”产热。在0[degree]C的单次冲动中，观察到平均约9 x 10-6 cal/g神经的正热产生：这是快速的，可能与冲动的活跃阶段有关。随后是一个相当缓慢的热吸收，平均约7 x 10[image]6 cal/g神经，持续约300 ms。以前的方法太慢，只能记录两者之间的差异，即“净热”，即约2 x 10-6 cal/g神经：这是在0[degree]C比18[degree]C高出约三分之一。Mala神经含有直径为20至0.3[mu]的纤维，大约一半的热量可能来自小于3.0u的纤维。在0[degree]C时，它们中的脉冲速度从1.4到0.1 m/s不等，因此脉冲在很长的时间间隔内到达记录热电偶。因此，所观察到的热产生过程是不同纤维中的正分量和负分量的结果，并且每个分量的实质部分被掩盖。因此，真实的正热量和负热量比观测到的要大得多：根据对速度分布的最可能的估计，在0[degree] C的单个脉冲中，它们分别约为14 x 10-6 cal/g和-12 x 10-6 cal/g。产热，如离子交换，可能是成比例的纤维表面，这在1克的马亚神经估计为10 - 4厘米2。如果纤维表面取50埃厚，则刚计算的热量，如果按每克表面材料计算，分别为2.8 × 10 - 3卡和-2.4 × 10-3卡。前者与肌肉抽搐时每克产生的热量大致相同。在脉冲通过期间，已知在轴质和外部流体之间存在Na和K离子的交换。当NaCl和KCl的等渗溶液混合时，会产生热。在脉冲过程中，很大一部分热量可能来自Na和K的交换。另一部分可能与可兴奋膜中发生的化学反应有关，该化学反应发生在伴随脉冲通过的渗透性变化周期期间。讨论了负产热问题。它不能与“泵回”Na和K离子联系起来;这是一个慢得多的过程，而且无论如何可能涉及正的热产生。这可能是吸热化学反应的标志，代表恢复的第一（厌氧）阶段，在渗透循环完成后发生在表面膜中。这个问题被认为是积极的和消极的阶段的热量生产是否可能是由于放电和充电，在动作电位，电容器驻留在可兴奋的膜。这样计算出的热量大小顺序是正确的，但根据目前的证据，时间关系似乎是完全错误的。测量在0[degree]C下缓慢重复刺激期间从马亚神经的每个脉冲逃逸的K的量。它在很大程度上取决于刺激的频率;在“零频率”时，它约为9 × 10-8摩尔/克×脉冲。
The "initial" heat production of a non-medullated nerve (Mala) has been reinvestigated with more rapid recording equipment than was previously available. In a single impulse at 0[degree]C a positive heat production was observed averaging about 9 x 10-6 cal/g nerve: this is rapid and is probably associated with the active phase of the impulse. It is followed by a rather slower heat absorption averaging about 7 x 10[image]6 cal/g nerve and lasting for about 300 ms. Previous methods were too slow to do more than record the difference between the two, the "net heat", viz. about 2 x 10-6 cal/g nerve: this is about one-third greater at 0[degree]C than at 18[degree]C. Mala nerves contain fibers from 20 to 0.3[mu] in diameter, and about half the heat is probably derived from fibres less than 3.0u. The velocities of impulses in them at 0[degree]C vary from 1.4 to 0.1 m/s, so impulses reach the recording thermojunctions throughout a long interval. Thus the observed course of the heat production is the resultant of positive and negative components in different fibres, and a substantial part of each is masked. The real positive and negative heats, therefore, are substantially greater than those observed: on the most likely estimate of velocity distribution, in a single impulse at 0[degree] C they are about 14 x 10-6 cal/g and -12 x 10-6 cal/g, respectively. Heat production, like ionic interchange, is probably proportional to fibre surface, which in 1 g of Maia nerve is estimated as 10 4 cm2. If the fibre surface is taken as 50 A thick, the heats just calculated, if reckoned per gram of surface material, are 2.8 x 10 3 cal and -2.4 x 10-3 cal, respectively. The former is about the same as the heat produced per gram in a muscle twitch. During the passage of an impulse there is known to be an interchange of Na and K ions between the axoplasm and the outside fluid. When isotonlc solutions of NaCl and KCl are mixed there is a production of heat. A substantial part of the heat during an impulse may be derived from the interchange of Na and K. Another part may be associated with chemical reactions occurring in the excitable membrane during the cycle of permeability change accompanying the passage of an impulse. The negative heat production is discussed. It cannot be connected with "pumping back" the Na and K ions; this is a much slower process and anyhow would probably involve a positive heat production. It may be a sign of endothermic chemical reactions, representing a first (anaerobic) stage in recovery, which occur in the surface membrane following the completion of the permeability cycle. The question is considered whether the positive and negative phases of the heat production could be due to the discharge and recharge, during the action potential, of the condenser residing in the excitable membrane. The heats so calculated are of the right order of size, but on present evidence the time relations seem to be quite wrong. The amount of K which escapes per impulse from Maia nerve during slow repetitive stimulation at 0[degree]C was measured. It depends greatly on frequency of stimulation; at "zero frequency" it was about 9 x 10-8 mole/g x impulse.