Margiotta J F, Pardi D
Department of Physiology and Biophysics, Mount Sinai School of Medicine, New York, New York 10029, USA.
Mol Pharmacol. 1995 Jul;48(1):63-71.
Nicotinic acetylcholine (ACh) receptors (AChRs) on ciliary ganglion neurons are positively regulated by elevated cAMP levels. Vasoactive intestinal peptide (VIP) can act as a first messenger in the regulation, because application of 1 microM VIP rapidly increases both neuronal cAMP levels and ACh sensitivity. We now report that high affinity receptors for a close VIP relative, pituitary adenylate cyclase-activating polypeptide (PACAP), are present on ciliary ganglion neurons and mediate the cAMP-dependent modulation of AChRs. Consistent with the presence of PACAP type I receptors, binding studies revealed sites on the neurons having approximately 1000-fold higher affinity for the 38- and 27-amino acid forms of PACAP than for VIP, and cAMP radio-immunoassays demonstrated that PACAP38 and PACAP27 are approximately 600-fold more potent agonists for mobilizing neuronal cAMP than is VIP. In accord with their higher affinity and potency, PACAP38 and -27 (both at 10 nM) increased neuronal ACh sensitivity by approximately 50% within 10 min, whereas VIP at the same low concentration was ineffective. The increased ACh sensitivity induced by 10 nM PACAP38 or PACAP27 or 1 microM VIP depends on coincident increases in cAMP levels, because treatment of neurons with adenylate cyclase inhibitors blocked both effects. The findings demonstrate the presence of functional PACAP type I receptors on ciliary ganglion neurons that preferentially recognize PACAP38 and -27 over VIP and act via adenylate cyclase to initiate cAMP-dependent enhancement of AChR function. Finally, we detected PACAP38-like material in ciliary ganglia, suggesting a role for the peptide in modulating neuronal AChRs in vivo.
睫状神经节神经元上的烟碱型乙酰胆碱（ACh）受体（AChRs）受cAMP水平升高的正向调节。血管活性肠肽（VIP）可作为该调节过程中的第一信使，因为施加1微摩尔VIP可迅速提高神经元cAMP水平和ACh敏感性。我们现在报告，睫状神经节神经元上存在与VIP密切相关的垂体腺苷酸环化酶激活多肽（PACAP）的高亲和力受体，并介导AChRs的cAMP依赖性调节。与I型PACAP受体的存在一致，结合研究显示，神经元上的位点对38个和27个氨基酸形式的PACAP的亲和力比对VIP的亲和力高约1000倍，cAMP放射免疫测定表明，PACAP38和PACAP27在动员神经元cAMP方面的激动剂效力比VIP高约600倍。与它们更高的亲和力和效力一致，PACAP38和-27（均为10纳摩尔）在10分钟内使神经元ACh敏感性增加约50%，而相同低浓度的VIP则无效。10纳摩尔PACAP38或PACAP27或1微摩尔VIP诱导的ACh敏感性增加取决于cAMP水平的同时升高，因为用腺苷酸环化酶抑制剂处理神经元可阻断这两种效应。这些发现证明睫状神经节神经元上存在功能性I型PACAP受体，它们优先识别PACAP38和-27而非VIP，并通过腺苷酸环化酶启动AChR功能的cAMP依赖性增强。最后，我们在睫状神经节中检测到PACAP38样物质，提示该肽在体内调节神经元AChRs方面的作用。
