Department of Physiology and Pharmacology, College of Medicine, Chang Gung University, Kwei-San, Tao-Yuan, Taiwan.
J Neurophysiol. 2012 Oct;108(7):2024-32. doi: 10.1152/jn.00361.2012. Epub 2012 Jul 5.
Na/K pump activity and metabolic rate are both higher during the day in the suprachiasmatic nucleus (SCN) that houses the circadian clock. Here we investigated the role of intracellular Na(+) and energy metabolism in regulating Na/K pump activity and neuronal excitability. Removal of extracellular K(+) to block the Na/K pump excited SCN neurons to fire at higher rates and return to normal K(+) to reactivate the pump produced rebound hyperpolarization to inhibit firing. In the presence of tetrodotoxin to block the action potentials, both zero K(+)-induced depolarization and rebound hyperpolarization were blocked by the cardiac glycoside strophanthidin. Ratiometric Na(+) imaging with a Na(+)-sensitive fluorescent dye indicated saturating accumulation of intracellular Na(+) in response to pump blockade with zero K(+). The Na(+) ionophore monensin also induced Na(+) loading and hyperpolarized the membrane potential, with the hyperpolarizing effect of monensin abolished in zero Na(+) or by pump blockade. Conversely, Na(+) depletion with Na(+)-free pipette solution depolarized membrane potential but retained residual Na/K pump activity. Cyanide inhibition of oxidative phosphorylation blocked the Na/K pump to depolarize resting potential and increase spontaneous firing in most cells, and to raise intracellular Na(+) levels in all cells. Nonetheless, the Na/K pump was incompletely blocked by cyanide but completely blocked by iodoacetate to inhibit glycolysis, indicating the involvement of both oxidative phosphorylation and glycolysis in fueling the Na/K pump. Together, the results indicate the importance of intracellular Na(+) and energy metabolism in regulating Na/K pump activity as well as neuronal excitability in the SCN neurons.
在包含生物钟的视交叉上核（SCN）中，钠钾泵的活性和代谢率在白天都更高。在这里，我们研究了细胞内钠离子和能量代谢在调节钠钾泵活性和神经元兴奋性中的作用。去除细胞外钾（K+）以阻断钠钾泵会使 SCN 神经元以更高的速率兴奋，并恢复正常 K+以重新激活泵，从而产生反弹超极化以抑制兴奋。在使用河豚毒素阻断动作电位的情况下，零 K+诱导的去极化和反弹超极化都被心脏糖苷哇巴因阻断。使用 Na+敏感荧光染料进行比率 Na+成像表明，在零 K+的情况下，泵阻断会导致细胞内 Na+的饱和积累。Na+离子载体莫能菌素也会诱导 Na+加载并使膜电位超极化，而莫能菌素的超极化作用在零 Na+或泵阻断时被消除。相反，用不含 Na+的玻璃微电极内液使 Na+耗尽会使膜电位去极化，但保留残余的钠钾泵活性。氰化物抑制氧化磷酸化会使钠钾泵去极化静息电位并增加大多数细胞的自发放电，并使所有细胞的细胞内 Na+水平升高。尽管如此，氰化物不完全阻断钠钾泵，但碘乙酸完全阻断钠钾泵以抑制糖酵解，表明氧化磷酸化和糖酵解都参与为钠钾泵提供燃料。总之，这些结果表明，细胞内钠离子和能量代谢在调节 SCN 神经元的钠钾泵活性和神经元兴奋性方面非常重要。
