Wang D, Gelband C H, Sumners C, Posner P
Department of Physiology, University of Florida College of Medicine, Gainesville 32610, USA.
J Neurophysiol. 1997 Aug;78(2):1013-20. doi: 10.1152/jn.1997.78.2.1013.
The chronotropic effect of angiotensin II (Ang II) was studied in cultured neurons from rat hypothalamus and brain stem with the use of the patch-clamp technique. Ang II (100 nM) increased the neuronal spontaneous firing rate from 0.8 +/- 0.3 (SE) Hz in control to 1.3 +/- 0.4 Hz (n = 7, P < 0.05). The amplitude of threshold stimulation was decreased by Ang II (100 nM) from 82 +/- 4 pA to 62 +/- 5 pA (n = 4, P < 0.05). These actions of Ang II were reversed by the angiotensin type 1 (AT1) receptor antagonist losartan (1 microM). In the presence of tetrodotoxin, Ang II (100 nM) significantly increased the frequency and the amplitude of the Cd2+-sensitive subthreshold activity of the cultured neurons. Ang II also stimulated the subthreshold early afterdepolarizations (EADs) to become fully developed action potentials. Similar to the action of Ang II, the protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA, 100 nM) increased the firing rate from 0.76 +/- 0.3 Hz to 2.3 +/- 0.5 Hz (n = 6, P < 0.05) and increased the neuronal subthreshold activity. After neurons were intracellularly dialyzed with PKC inhibitory peptide (PKCIP, 5 microM), PMA alone, Ang II alone, or PMA plus Ang II no longer increased the action potential firing initiated from the resting membrane potential level. However, superfusion of PMA plus Ang II or Ang II alone increased the number of EADs that reached threshold and produced action potentials even in the presence of PKCIP (5 microM, n = 4). The actions of Ang II could also be mimicked by depolarizing pulse and K+ channel blockers (tetraethylammonium chloride or 4-aminopyridine). These results indicate that Ang II by activation of AT1 receptors increases neuronal excitability and firing frequency, and that this may involve both PKC dependent and -independent mechanisms.
采用膜片钳技术，研究了血管紧张素II（Ang II）对大鼠下丘脑和脑干培养神经元的变时性作用。Ang II（100 nM）使神经元自发放电频率从对照时的0.8±0.3（SE）Hz增加到1.3±0.4 Hz（n = 7，P < 0.05）。Ang II（100 nM）使阈刺激幅度从82±4 pA降至62±5 pA（n = 4, P < 0.05）。血管紧张素1型（AT1）受体拮抗剂氯沙坦（1 microM）可逆转Ang II的这些作用。在存在河豚毒素的情况下，Ang II（100 nM）显著增加了培养神经元对镉离子敏感的阈下活动的频率和幅度。Ang II还刺激阈下早期后去极化（EADs）转变为完全发育的动作电位。与Ang II的作用相似，蛋白激酶C（PKC）激活剂佛波醇12 - 肉豆蔻酸酯13 - 乙酸酯（PMA，100 nM）使放电频率从0.76±0.3 Hz增加到2.3±0.5 Hz（n = 6，P < 0.05），并增加了神经元的阈下活动。在用PKC抑制肽（PKCIP，5 microM）对神经元进行细胞内透析后，单独使用PMA、单独使用Ang II或PMA加Ang II均不再增加从静息膜电位水平引发的动作电位发放。然而，即使在存在PKCIP（5 microM，n = 4）的情况下，PMA加Ang II或单独使用Ang II的灌流仍增加了达到阈值并产生动作电位的EADs数量。Ang II的作用也可被去极化脉冲和钾通道阻滞剂（氯化四乙铵或4 - 氨基吡啶）模拟。这些结果表明，Ang II通过激活AT1受体增加神经元兴奋性和放电频率，这可能涉及PKC依赖性和非依赖性机制。
