Zhu M, Sumners C, Gelband C H, Posner P
Department of Physiology, College of Medicine and McKnight Brain Institute, University of Florida, Gainesville, Florida 32610, USA.
J Neurophysiol. 2001 May;85(5):2177-83. doi: 10.1152/jn.2001.85.5.2177.
Previously, we determined that angiotensin II (Ang II) elicits an Ang II type 2 (AT(2)) receptor-mediated increase of neuronal delayed rectifier K(+) (I(KV)) current in neuronal cultures from newborn rat hypothalamus and brain stem. This requires generation of lipoxygenase (LO) metabolites of arachidonic acid (AA) and activation of serine/threonine phosphatase type 2A (PP-2A). Enhancement of I(KV) results in a decrease in net inward current during the action potential (AP) upstroke as well as shortening of the refractory period, which may lead to alterations in neuronal firing rate. Thus, in the present study, we used whole-cell current clamp recording methods to investigate the AT(2) receptor-mediated effects of Ang II on the firing rate of cultured neurons from the hypothalamus and brain stem. At room temperature, these neurons exhibited spontaneous APs with an amplitude of 77.72 +/- 2.7 mV (n = 20) and they fired at a frequency of 0.8 +/- 0.1 Hz (n = 11). Most cells had a prolonged early after-depolarization that followed an initial fully developed AP. Superfusion of Ang II (100 nM) plus losartan (LOS, 1 microM) to block Ang II type 1 receptors elicited a significant chronotropic effect that was reversed by the AT(2) receptor inhibitor PD 123,319 (1 microM). LOS alone had no effect on any of the parameters measured. The chronotropic effect of Ang II was reversed by the general LO inhibitor 5,8,11,14-eicosatetraynoic acid (10 microM) or by the selective PP-2A inhibitor okadaic acid (1 nM) and was mimicked by the 12-LO metabolite of AA 12-(S)-hydroxy-(5Z, 8Z, 10E, 14Z)-eicosatetraynoic acid. These data indicate that Ang II elicits an AT(2) receptor-mediated increase in neuronal firing rate, an effect that involves generation of LO metabolites of AA and activation of PP-2A.
此前，我们确定血管紧张素II（Ang II）可在新生大鼠下丘脑和脑干的神经元培养物中引发血管紧张素II 2型（AT(2)）受体介导的神经元延迟整流钾（I(KV)）电流增加。这需要花生四烯酸（AA）的脂氧合酶（LO）代谢产物的生成以及2A型丝氨酸/苏氨酸磷酸酶（PP-2A）的激活。I(KV)的增强导致动作电位（AP）上升期间内向电流净减少以及不应期缩短，这可能导致神经元放电频率改变。因此，在本研究中，我们使用全细胞电流钳记录方法来研究Ang II的AT(2)受体介导的对下丘脑和脑干培养神经元放电频率的影响。在室温下，这些神经元表现出自发性AP，幅度为77.72±2.7 mV（n = 20），放电频率为0.8±0.1 Hz（n = 11）。大多数细胞在最初完全发育的AP后有一个延长的早期去极化后电位。用Ang II（100 nM）加氯沙坦（LOS，1 μM）灌注以阻断血管紧张素II 1型受体可引发显著的变时效应，该效应被AT(2)受体抑制剂PD 123,319（1 μM）逆转。单独使用LOS对所测量的任何参数均无影响。Ang II的变时效应被通用的LO抑制剂5,8,11,14-二十碳四烯酸（1 μM）或选择性PP-2A抑制剂冈田酸（1 nM）逆转，并被AA的12-LO代谢产物12-(S)-羟基-(5Z, 8Z, 10E, 14Z)-二十碳四烯酸模拟。这些数据表明，Ang II可引发AT(2)受体介导的神经元放电频率增加，这一效应涉及AA的LO代谢产物的生成和PP-2A的激活。
