MECHANISMS OF SIGNAL TRANSDUCTION OF CARDIAC OPIOID RECEPTOR STIMULATION

阿片肽(OP)与儿茶酚胺(CA)从神经协同释放 心脏心肌细胞的末端也产生和分泌阿片类物质。 并具有阿片肽受体(OPR)。因此，我们建议OP也 可能具有突触后心脏细胞内信号转导作用 与β-肾上腺素能受体产生强烈的“串音” (β-AR)刺激途径。这项工作的重点是确定 OPR刺激是否影响β-AR刺激的效果 互动机制的本质(S)。在一个完整的孤立的 心脏制剂(用6-羟基多巴胺预处理以从 周围神经末梢)峰值收缩压增加到217% 由CA去甲肾上腺素(NE；10-7M)控制，添加 Delta-OPR激动剂亮氨酸脑啡肽(LE；10-8M)导致显著的 在15-25分钟内将开发压力降低到对照的66%。这个 OPR拮抗剂纳洛酮(10-8M)快速加入LE+NE缓冲液 逆转LE效应(&lt；1-2min)至对照收缩压的188%。 10-8M LE可有效抑制去甲肾上腺素的正性肌力作用 包括仅在这种浓度下，cAMP的刺激增加 对收缩压和cAMP组织含量无明显影响。一个 CAMP的非水解性类似物，CPTcAMP，在3x10-5M时收缩压升高 压力达到对照的176%，但LE(10-8M)+CPTcAMP不能抵消作用 正性变力作用。类似地，在福斯科林灌流期间， 使收缩压升高至200%，10~(-8)M LE也无作用。 在用百日咳毒素(催化腺嘌呤)预处理后 GI/G0蛋白α亚基的核苷酸核糖化并抑制 对激动剂的反应)，LE不再能抑制BetaAR的作用 刺激。在单个心肌细胞中也观察到了类似的结果 哪些细胞内钙离子和Ica可以被测量。我们的结论是 LE的潜在影响是由于LE的一种特殊的“串扰” β-AR刺激通路上的信号级联反应 百日咳毒素敏感G蛋白参与抑制 腺苷环化酶。因此，这种相互作用可以调节 β-肾上腺素能对心脏做功的影响并通过 防止紧张期间代谢底物供需失衡 心脏应激，如运动或缺血。

Opioid peptides (OP) are coreleased with catecholamines (CA) from nerve terminals in the heart cardiac myocytes also produce and secrete opioids and have opioid peptide receptors (OPR). Thus we proposed that OP also may have a postsynaptic cardiac intracellular signalling role which involves a potent "cross-talk" with the beta-adrenergic receptor (beta-AR) stimulation pathway. The focus of this work was to identify whether OPR stimulation influences the effects of beta-AR stimulation and the nature of the mechanism(s) of interaction. In an intact isolated heart preparation (pretreated with 6-hydroxy-dopamine to deplete CA from peripheral nerve endings) peak systolic pressure was increased to 217% of control by the CA norepinephrine (NE;10-7M), addition of the delta-OPR agonist leucine enkephalin (LE;10-8M) resulted in a marked reduction in developed pressure to 66% of control within 15-25min. The OPR antagonist naloxone (10-8M) added to the LE+NE buffer rapidly reversed the LE effect (<1-2min) to 188% of control systolic pressure. Although 10-8M LE potently inhibited the positive inotropic effect of NE including the stimulated increase in cAMP, alone, at this concentration it had no effect on systolic pressure nor tissue content of cAMP. A non-hydrolyzable analog of cAMP, CPTcAMP, at 3x10-5M increased systolic pressure to 176% of control but LE (10-8M)+CPTcAMP could not counter act the positive inotropic effect. Similarly during perfusion with forskolin, which raised systolic pressure to 200%, 10-8M LE also had no effect. Following pretreatment with pertussis toxin, (which catalyzes the adenine nucleotide ribosylation of Gi/G0-protein alpha subunits and inhibits the response to agonists), LE could no longer inhibit the effects of betaAR stimulation. Similar results were observed in single cardiac myocytes in which cytosolic Ca2+ and Ica could be measured. We conclude that the potent effects of LE are due to a specific "cross-talk" of the LE signalling cascade on the betaAR stimulation pathway and mediated by a pertussis toxin-sensitive G protein involved in the inhibition of adenylyl cyclase. This interaction may thus regulate the magnitude of beta-adrenergic effects on cardiac work and provide protection by preventing metabolic substrate supply/demand imbalance during intense cardiac stress such as exercise or ischemia.