Chen J, He L, Dinger B, Fidone S
Department of Physiology, University of Utah School of Medicine, Salt Lake City 84108, USA.
Neuroscience. 2000;95(1):283-91. doi: 10.1016/s0306-4522(99)00399-1.
The carotid body is an arterial chemosensory organ which responds to multiple natural and pharmacological stimuli, including hypoxia and nicotine. Numerous studies have investigated the initial molecular events which activate chemosensory type I cells in the carotid body, but less attention has been focused on later steps in the transduction cascade, which mediate neurotransmitter release from type I cells and excitation of chemoreceptor afferent fibers in the carotid sinus nerve. In the present study, we examined the effects of a highly specific inhibitor of calcium/calmodulin-dependent kinase II, KN-62, and a calmodulin inhibitor, trifluoperazine, on carotid sinus nerve activity and catecholamine release evoked from rabbit carotid bodies superfused in vitro. KN-62 did not alter sinus nerve activity and catecholamine release evoked by hypoxia, but this agent significantly reduced nerve activity and neurotransmitter release evoked by 100 microM nicotine. Trifluoperazine (10 microM), likewise inhibited activity evoked by nicotine, as well as hypoxia. Basal levels of nerve activity and catecholamine release (established in superfusate equilibrated with 100% O2) were unaffected by all drug treatments. Separate biochemical experiments showed that Ca2+/calmodulin-dependent incorporation of 32P into carotid body particulate proteins is significantly reduced following incubation of intact carotid bodies in nicotine, but not following exposure to hypoxia. Our observations suggest that excitation of the carotid body by diverse stimuli may involve the activation of distinct, stimulus-specific transduction pathways. Furthermore, these data correlate with our previous findings which showed that hypoxia, on the one hand, and nicotine on the other, evoke the preferential release of either dopamine or norepinephrine, respectively, from carotid bodies incubated in vitro.
颈动脉体是一种动脉化学感受器官，可对多种自然和药理刺激作出反应，包括低氧和尼古丁。众多研究调查了激活颈动脉体化学感受性I型细胞的初始分子事件，但较少关注转导级联反应的后续步骤，这些步骤介导I型细胞释放神经递质以及颈动脉窦神经中化学感受传入纤维的兴奋。在本研究中，我们检测了钙/钙调蛋白依赖性激酶II的高度特异性抑制剂KN-62和钙调蛋白抑制剂三氟拉嗪对体外灌流的兔颈动脉体诱发的颈动脉窦神经活动和儿茶酚胺释放的影响。KN-62并未改变低氧诱发的窦神经活动和儿茶酚胺释放，但该药物显著降低了100微摩尔尼古丁诱发的神经活动和神经递质释放。三氟拉嗪（10微摩尔）同样抑制尼古丁以及低氧诱发的活动。所有药物处理均未影响神经活动和儿茶酚胺释放的基础水平（在与100%氧气平衡的灌流液中测定）。单独的生化实验表明，完整的颈动脉体在尼古丁中孵育后，Ca2+/钙调蛋白依赖性的32P掺入颈动脉体颗粒蛋白的过程显著减少，但暴露于低氧后并未减少。我们的观察结果表明，不同刺激对颈动脉体的兴奋可能涉及激活不同的、刺激特异性的转导途径。此外，这些数据与我们之前的发现相关，即一方面低氧，另一方面尼古丁，分别从体外孵育的颈动脉体中优先释放多巴胺或去甲肾上腺素。
