Broad R M, McDonald T J, Brodin E, Cook M A
Department of Pharmacology, University of Western Ontario, London, Canada.
Am J Physiol. 1992 Mar;262(3 Pt 1):G525-31. doi: 10.1152/ajpgi.1992.262.3.G525.
A perifused preparation of guinea pig myenteric nerve varicosities (synaptosomes) was used to determine the characteristics of evoked tachykinin release and the inhibition of such release by adenosine analogues. Release of substance P-like immunoreactivity (SP-LI) and neurokinin A-like immunoreactivity (NKA-LI) was evoked by elevated extracellular [K+] in a reversible and repeatable manner. This release was completely abolished in the absence of extracellular Ca2+. Perifusion in the presence of 5'-N-ethylcarboxamidoadenosine (NECA), a nonselective A1/A2 adenosine receptor agonist, decreased K(+)-evoked release of SP-LI and NKA-LI compared with that in the absence of the nucleoside. Similar decrements in peptide release were obtained with N6-cyclopentyl adenosine (CPA), a selective A1 agonist, and 2-[p-(2-carboxyethyl)]phenethylamino-5'-N-ethyl-carboxamidoadenosi ne (CGS 21680), a selective A2 agonist. Response to all nucleosides was graded. Potency order of adenosine analogues was CPA greater than NECA much greater than CGS 21680. Inhibition due to the nucleosides was diminished in the presence of the highly selective A1-receptor antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) while perifusion in the presence of DPCPX alone did not alter evoked release of either peptide. These findings provide direct measurements of inhibitory effects of adenine nucleosides on the release, from enteric nerve endings, of endogenous neuromediators SP and NKA. The findings also directly demonstrate the presence of functional adenosine receptors of the A1 subtype on enteric nerve endings coupled negatively to release of tachykinins. The presence of A2 receptors on enteric nerve endings is neither supported nor excluded.
采用豚鼠肠肌间神经膨体（突触体）的灌流制备物来确定诱发速激肽释放的特征以及腺苷类似物对这种释放的抑制作用。细胞外[K⁺]升高以可逆且可重复的方式诱发了P物质样免疫反应性（SP-LI）和神经激肽A样免疫反应性（NKA-LI）的释放。在无细胞外Ca²⁺的情况下，这种释放完全被消除。在存在非选择性A1/A2腺苷受体激动剂5'-N-乙基羧基酰胺腺苷（NECA）的情况下进行灌流，与不存在该核苷时相比，K⁺诱发的SP-LI和NKA-LI释放减少。使用选择性A1激动剂N⁶-环戊基腺苷（CPA）和选择性A2激动剂2-[对-(2-羧乙基)]苯乙氨基-5'-N-乙基-羧基酰胺腺苷（CGS 21680）也获得了类似的肽释放减少。对所有核苷的反应呈剂量依赖性。腺苷类似物的效力顺序为CPA大于NECA远大于CGS 21680。在存在高度选择性A1受体拮抗剂1,3-二丙基-8-环戊基黄嘌呤（DPCPX）的情况下，核苷引起的抑制作用减弱，而单独在DPCPX存在下进行灌流不会改变两种肽的诱发释放。这些发现直接测量了腺嘌呤核苷对肠神经末梢释放内源性神经介质SP和NKA的抑制作用。这些发现还直接证明了肠神经末梢上存在与速激肽释放呈负偶联的A1亚型功能性腺苷受体。既不支持也不排除肠神经末梢上存在A2受体。
