Alberi S, Dreifuss J J, Raggenbass M
Department of Physiology, University Medical Centre, Geneva, Switzerland.
Eur J Neurosci. 1997 Dec;9(12):2605-12. doi: 10.1111/j.1460-9568.1997.tb01690.x.
The neuropeptide oxytocin can depolarize parasympathetic preganglionic neurons in the dorsal motor nucleus of the vagus nerve of the rat by generating a sustained inward current, which is sodium-dependent and tetrodotoxin-insensitive. The second messenger activated by oxytocin receptor binding is, however, not yet known. In the present study, we attempted to characterize it by using the whole-cell recording technique and brainstem slices. When loaded with GTP-gamma-S, a non-hydrolysable analogue of GTP, vagal neurons generated a persistent inward current in the absence of agonist and the oxytocin effect was suppressed, suggesting that the peptide-evoked current was mediated by G-protein activation. Loading vagal neurons with the calcium chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N',-tetraacetic acid (BAPTA) suppressed a calcium-dependent, slowly decaying potassium aftercurrent but did not affect the oxytocin response, suggesting that the latter was not mediated by an agonist-induced increase in the intracellular calcium concentration. Protein kinase C (PKC) activation was probably not involved, since the peptide-evoked current was not modified by loading neurons with the PKC inhibitor H7. Thus, the oxytocin-evoked current in vagal neurons was probably not mediated by phospholipase C-beta (PLC-beta) activation. Loading neurons with 8-Br-cAMP or with an adenylyl cyclase activator (forskolin) reduced the oxytocin-evoked current by about half. SQ 22536, an adenylyl cyclase inhibitor, reduced this current by a similar amount. However, the peptide-evoked current was unaffected by Rp-cAMPS and Sp-cAMPS, an inhibitor and an activator, respectively, of cAMP-dependent protein kinase (PKA). We suggest that oxytocin activates two distinct signalling pathways in vagal neurons: one which is cAMP-dependent, but PKA-independent, and one, unidentified, which is PLC-beta-and cAMP-independent. Each pathway accounts for about half of the peptide effect and both appear to involve G-protein activation.
神经肽催产素可通过产生一种持续内向电流，使大鼠迷走神经背运动核中的副交感神经节前神经元去极化，该电流依赖于钠且对河豚毒素不敏感。然而，催产素受体结合所激活的第二信使尚不清楚。在本研究中，我们试图通过使用全细胞记录技术和脑干切片来对其进行表征。当用GTP的非水解类似物GTP-γ-S加载时，迷走神经元在没有激动剂的情况下产生持续内向电流，且催产素效应受到抑制，这表明该肽诱发的电流是由G蛋白激活介导的。用钙螯合剂1,2-双(2-氨基苯氧基)乙烷-N,N,N',N'-四乙酸(BAPTA)加载迷走神经元可抑制钙依赖性、缓慢衰减的钾电流，但不影响催产素反应，这表明后者不是由激动剂诱导的细胞内钙浓度升高介导的。蛋白激酶C(PKC)激活可能不参与其中，因为加载PKC抑制剂H7的神经元中，该肽诱发的电流未被改变。因此，迷走神经元中催产素诱发的电流可能不是由磷脂酶C-β(PLC-β)激活介导的。用8-溴-cAMP或腺苷酸环化酶激活剂(福斯高林)加载神经元可使催产素诱发的电流减少约一半。腺苷酸环化酶抑制剂SQ 22536使该电流减少相似的量。然而，该肽诱发的电流不受cAMP依赖性蛋白激酶(PKA)的抑制剂Rp-cAMPS和激活剂Sp-cAMPS的影响。我们认为，催产素在迷走神经元中激活两条不同的信号通路：一条是依赖cAMP但不依赖PKA的通路，另一条是未确定的、不依赖PLC-β和cAMP的通路。每条通路约占该肽效应的一半，且两者似乎都涉及G蛋白激活。
