Maeno T, Enomoto K, Hara N, Sawada M, Ichinose M
Department of Physiology, Shimane Medical University, Izumo, Japan.
Jpn J Physiol. 1995;45(1):85-95. doi: 10.2170/jjphysiol.45.85.
Toxic and nontoxic effects of ouabain were investigated on frog neuromuscular preparation by measuring the mean quantal content of endplate potentials elicited during repetitive nerve stimulation. In the untreated normal muscles, application of 10 microM ouabain gave rise to a slow exponential increase in the transmitter release (toxic ouabain effect) with a certain delay. This delay was increased with either 100 microM amiloride, a Na(+)-Ca2+ exchange blocker, or the intracellular loading of 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA), a specific intracellular Ca2+ chelator. Measurements of frequency augmentation-potentiation (FAP) revealed a specific nontoxic effect of ouabain: 1 microM ouabain pivoted the long-linear FAP relation counter-clockwise without altering the intercept on the ordinate. Contrary to their action in the toxic effect, both 100 microM amiloride and the intracellular loading of BAPTA failed to counteract the nontoxic effect of 1 microM ouabain. The present results suggest that the toxic and nontoxic effects of ouabain are of different entities. The ouabain-sensitive subtype of Na+,K(+)-ATPase, which is abundant in neural tissues, seems to play a specific role in the process of nontoxic potentiation of transmitter release.
通过测量重复神经刺激期间诱发的终板电位的平均量子含量，研究了哇巴因对青蛙神经肌肉标本的毒性和非毒性作用。在未经处理的正常肌肉中，施加10微摩尔哇巴因会导致递质释放缓慢呈指数增加（哇巴因的毒性作用），且有一定延迟。用100微摩尔氨氯吡咪（一种钠钙交换阻滞剂）或用1,2-双（2-氨基苯氧基）乙烷-N,N,N',N'-四乙酸（BAPTA，一种特异性细胞内钙螯合剂）进行细胞内加载后，这种延迟会增加。频率增强-增强作用（FAP）测量揭示了哇巴因的一种特定非毒性作用：1微摩尔哇巴因使长线性FAP关系逆时针旋转，而不改变纵坐标上的截距。与它们在毒性作用中的作用相反，100微摩尔氨氯吡咪和BAPTA的细胞内加载均未能抵消1微摩尔哇巴因的非毒性作用。目前的结果表明，哇巴因的毒性和非毒性作用是不同的实体。在神经组织中丰富的钠钾ATP酶的哇巴因敏感亚型，似乎在递质释放的非毒性增强过程中起特定作用。
