Instituto Teófilo Hernando, Departamento de Farmacología y Terapéutica, Facultad de Medicina, Universidad Autónoma de Madrid, and Servicio de Farmacología Clínica, Instituto de Investigación Sanitaria, Hospital Universitario de la Princesa, Madrid, Spain.
Cell Calcium. 2011 Oct;50(4):332-42. doi: 10.1016/j.ceca.2011.06.002. Epub 2011 Jul 7.
The augmentation of neurotransmitter and hormone release produced by ouabain inhibition of plasmalemmal Na+/K+-ATPase (NKA) is well established. However, the mechanism underlying this action is still controversial. Here we have shown that in bovine adrenal chromaffin cells ouabain diminished the mobility of chromaffin vesicles, an indication of greater number of docked vesicles at subplasmalemmal exocytotic sites. On the other hand, ouabain augmented the number of vesicles undergoing exocytosis in response to a K+ pulse, rather than the quantal size of single vesicles. Furthermore, ouabain produced a tiny and slow Ca2+ release from the endoplasmic reticulum (ER) and gradually augmented the transient elevations of the cytosolic Ca2+ concentrations ([Ca2+]c) triggered by K+ pulses. These effects were paralleled by gradual increments of the transient catecholamine release responses triggered by sequential K+ pulses applied to chromaffin cell populations treated with ouabain. Both, the increases of K+-elicited [Ca2+]c and secretion in ouabain-treated cells were blocked by thapsigargin (THAPSI), 2-aminoethoxydiphenyl borate (2-APB) and caffeine. These results are compatible with the view that ouabain may enhance the ER Ca2+ load and facilitate the Ca2+-induced-Ca2+ release (CICR) component of the [Ca2+]c signal generated during K+ depolarisation. This could explain the potentiating effects of ouabain on exocytosis.
哇巴因抑制质膜 Na+/K+-ATP 酶（NKA）导致神经递质和激素释放增加已得到充分证实。然而，这种作用的机制仍存在争议。在这里，我们已经表明，在牛肾上腺嗜铬细胞中，哇巴因降低了嗜铬小泡的流动性，这表明在亚质膜胞吐位点有更多的停靠小泡。另一方面，哇巴因增加了对 K+脉冲响应的发生胞吐的小泡数量，而不是单个小泡的量子大小。此外，哇巴因从内质网（ER）产生微小而缓慢的 Ca2+释放，并逐渐增加 K+脉冲触发的细胞溶质 Ca2+浓度 ([Ca2+]c) 的瞬时升高。这些效应与哇巴因处理的嗜铬细胞群体中连续 K+脉冲触发的瞬时光肾上腺素释放反应的逐渐增加平行。哇巴因处理细胞中 K+诱发的 [Ca2+]c 和分泌的增加均被 thapsigargin (THAPSI)、2-氨基乙氧基二苯硼酸盐 (2-APB) 和咖啡因阻断。这些结果与以下观点一致：哇巴因可能会增加 ER Ca2+负荷，并促进 K+去极化期间产生的 [Ca2+]c 信号中 Ca2+-诱导的 Ca2+释放 (CICR) 成分。这可以解释哇巴因对胞吐作用的增强效应。
