Lalley P M, Pierrefiche O, Bischoff A M, Richter D W
II. Institut Physiologisches, Universität Goettingen, Humboldtallee, Germany.
J Neurophysiol. 1997 Mar;77(3):1119-31. doi: 10.1152/jn.1997.77.3.1119.
The adenosine 3',5'-cyclic monophosphate (cAMP)-dependent protein kinase (PKA) second-messenger system influences neuronal excitability by modulating voltage-regulated and transmitter-activated channels. In this study we investigated the influence of the cAMP-PKA system on the excitability of expiratory (E) neurons in the caudal medulla of anesthetized, paralyzed, and artificially ventilated adult cats. We intracellularly injected the PKA inhibitors cAMP-dependent PKA inhibitor 5-22 amide (Walsh inhibitory peptide) and Rp-adenosine 3',5'-cyclic monophosphothioate triethylamine (Rp-cAMPS), the PKA activator Sp-adenosine 3',5'-cyclic monophosphothioate triethylamine (Sp-cAMPS), and the adenylyl cyclase activator forskolin and measured membrane potential, neuronal input resistance, and synaptic membrane currents. Inhibition of cAMP-PKA activity by Walsh inhibitory peptide or Rp-cAMPS injections hyperpolarized neurons, decreased input resistance, and depressed spontaneous bursts of action potentials. Action potential duration was shortened and afterhyperpolarizations were increased. Inhibitory synaptic currents increased significantly. Stimulation of cAMP-PKA activity by Sp-cAMPS or forskolin depolarization neurons and increased input resistance. Spontaneous inhibitory synaptic currents were reduced and excitatory synaptic currents were increased. Rp-cAMPs depressed stimulus-evoked excitatory postsynaptic potentials and currents, whereas Sp-cAMPS increased them. Sp-cAMPS also blocked postsynaptic inhibition of E neurons by 8-hydroxy-dipropylaminotetralin, a serotonin-1A (5-HT-1A) receptor agonist that depresses neuronal cAMP-PKA activity. To determine the predominant effect of G protein-mediated neuromodulation of E neurons, we injected guanosine-5'-O-(3-thiotriphosphate) tetralithium salt (GTP-gamma-S), an activator of both stimulatory and inhibitory G proteins. GTP-gamma-S hyperpolarized E neurons, reduced input resistance, and increased action potential afterhyperpolarization. We conclude that the intracellular cAMP-PKA messenger system play an important role in the activity-dependent modulation of excitability in E neurons of the caudal medulla. In addition, the cAMP-PKA pathway itself is downregulated during activation of 5-HT-1A receptors.
3',5'-环磷酸腺苷（cAMP）依赖性蛋白激酶（PKA）第二信使系统通过调节电压门控通道和递质激活通道来影响神经元兴奋性。在本研究中，我们调查了cAMP-PKA系统对麻醉、麻痹并人工通气的成年猫延髓尾部呼气（E）神经元兴奋性的影响。我们向细胞内注射了PKA抑制剂cAMP依赖性PKA抑制剂5-22酰胺（沃尔什抑制肽）和Rp-3',5'-环磷硫酰胺三乙胺（Rp-cAMPS）、PKA激活剂Sp-3',5'-环磷硫酰胺三乙胺（Sp-cAMPS）以及腺苷酸环化酶激活剂福斯高林，并测量了膜电位、神经元输入电阻和突触膜电流。注射沃尔什抑制肽或Rp-cAMPS抑制cAMP-PKA活性会使神经元超极化，降低输入电阻，并抑制动作电位的自发爆发。动作电位持续时间缩短，超极化后电位增加。抑制性突触电流显著增加。Sp-cAMPS或福斯高林刺激cAMP-PKA活性会使神经元去极化并增加输入电阻。自发抑制性突触电流减少，兴奋性突触电流增加。Rp-cAMPS抑制刺激诱发的兴奋性突触后电位和电流，而Sp-cAMPS则增强它们。Sp-cAMPS还可阻断8-羟基-二丙基氨基四氢萘对E神经元的突触后抑制，8-羟基-二丙基氨基四氢萘是一种血清素-1A（5-HT-1A）受体激动剂，可抑制神经元cAMP-PKA活性。为了确定G蛋白介导的E神经元神经调节的主要作用，我们注射了鸟苷-5'-O-（3-硫代三磷酸）四锂盐（GTP-γ-S），它是刺激性和抑制性G蛋白的激活剂。GTP-γ-S使E神经元超极化，降低输入电阻，并增加动作电位超极化后电位。我们得出结论，细胞内cAMP-PKA信使系统在延髓尾部E神经元兴奋性的活动依赖性调节中起重要作用。此外，在5-HT-1A受体激活过程中，cAMP-PKA途径本身会被下调。
