Donnelly David F
Department of Pediatrics, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520, USA.
J Appl Physiol (1985). 2008 May;104(5):1394-401. doi: 10.1152/japplphysiol.01169.2007. Epub 2008 Feb 28.
The mechanism by which action potentials (APs) are generated in afferent nerve fibers in the carotid body is unknown, but it is generally speculated to be release of an excitatory transmitter and synaptic depolarizing events. However, previous results suggested that Na(+) channels in the afferent nerve fibers play an important role in this process. To better understand the potential mechanism by which Na(+) channels may generate APs, a mathematical model of chemoreceptor nerve fibers that incorporated Hodgkin-Huxley-type Na(+) channels with kinetics of activation and inactivation, as determined previously from recordings of petrosal chemoreceptor neurons, was constructed. While the density of Na(+) channels was kept constant, spontaneous APs arose in nerve terminals as the axonal diameter was reduced to that in rat carotid body. AP excitability and pattern were similar to those observed in chemoreceptor recordings: 1) a random pattern at low- and high-frequency discharge rates, 2) a high sensitivity to reductions in extracellular Na(+) concentration, and 3) a variation in excitability that increased with AP generation rate. Taken together, the results suggest that an endogenous process in chemoreceptor nerve terminals may underlie AP generation, a process independent of synaptic depolarizing events.
颈动脉体传入神经纤维中动作电位（APs）产生的机制尚不清楚，但一般推测是兴奋性递质的释放和突触去极化事件。然而，先前的结果表明，传入神经纤维中的Na(+)通道在这一过程中起重要作用。为了更好地理解Na(+)通道产生APs的潜在机制，构建了一个化学感受器神经纤维的数学模型，该模型纳入了具有激活和失活动力学的霍奇金-赫胥黎型Na(+)通道，其动力学是先前从岩神经化学感受器神经元的记录中确定的。当Na(+)通道密度保持恒定时，随着轴突直径减小到大鼠颈动脉体中的轴突直径，神经末梢出现自发APs。AP的兴奋性和模式与化学感受器记录中观察到的相似：1）在低频和高频放电率时为随机模式，2）对细胞外Na(+)浓度降低高度敏感，3）兴奋性随AP产生率增加而变化。综上所述，结果表明化学感受器神经末梢中的内源性过程可能是AP产生的基础，这一过程独立于突触去极化事件。
