Molecular Biological Studies on the Action Mechanisms of Motilin and its Receptor

胃动素是一种由22个氨基酸残基组成的多肽，最初是从猪的十二指肠粘膜中分离出来的。胃动素的主要功能是加速胃排空和明显启动消化间迁移收缩（IMC）。循环胃动素水平的节律性振荡，每90-120分钟出现一次峰值，与胃肠道ii期运动活动的出现密切相关。此外，在清醒的狗和人的消化间期静脉输注胃动素可引起十二指肠前区imc。体内研究表明，阿托品阻断胆碱能可消除胃动素对胃底囊和胃窦囊的刺激作用，胃动素可增加失神经胃的IMC，但不能增加空肠的IMC。因此，体液和神经机制都被认为是运动素作用的原因。然而，在细胞和分子水平上，胃动素对胃肠运动的作用机制尚不清楚。我们假设胃动素受体存在于兔胃窦和十二指肠平滑肌组织中，并试图证明^<125>l-胃动素与其受体直接结合。^<125>l-胃动素与十二指肠肌片的特异性结合最初是通过其直接结合和被各种非标记类似物（包括红霉素衍生物）取代^<125>l-胃动素来证明的。然而，由于一些未知的原因，l-胃动素对离体平滑肌膜的特异性结合尚未得到证实。我们目前正试图证明胃动素可能通过突触前神经末梢起作用，从而释放乙酰胆碱或其他神经递质。同时，我们制备了高放射性的胃动素配体，在13号位置用蛋氨酸取代亮氨酸，并在胃动素序列的低生物活性位点添加酪氨酸，以保持高特异性的结合活性。目前我们正在继续进行^<125 b> l-胃动素与兔胃窦和十二指肠平滑肌细胞膜结合的研究。少

Motilin is a polypeptide consisting of 22 amino acid residues and was originally isolated from the duodenal mucosa of hogs The major functions of motilin appear to be the acceleration of gastric emptying and the apparent initiation of the interdigestive migrating contractions (IMC). Rhythmic oscillations of circulating motilin levels, with peaks occuring every 90-120 min, correlate well with the appearance of phase Ill motor activity in the gastrointestinal tract. Furthermore, intravenous infusion of motilin in -concious dogs and humans during the interdigestive period initiated IMCs in the anteroduodenal region. In vivo studies demonstrate that cholinergic blockade with atropine abolished the stimulating effect of motilin in fundic and antral pouches of stomach and motilin increases IMC in denervated stomach but not denervated jejunum in dogs. Thus, both humoral and neural mechanisms have been postulated to be responsible for the action of motilin. However, the mechanism responsible f … More or the action of motilin on gastrointestinal motility is unclear at the cellular and molecular levels. We postulated the existence of motilin receptors on rabbit antral and duodenal smooth muscle tissues and attempted the demonstration of direct binding of ^<125>l-motilin to its receptors. The specific binding of ^<125>l-motilin to duodenal muscle slice was initially demonstrated by both its direct binding and displacement of ^<125>l-motilin by a variety of non-labeled analogues including erythromycin derivatives. However, the specific binding of ^<125>l-motilin to isolated smooth muscle membranes was not confirmed by some unknown reasons. We are currently trying to show that motilin may act through presynaptic nerve endings that may release acetylcholine or other neurotransmitters. At the same time we have prepared highly radioactive motilin ligands with substitution of methionin for leucine at position 13 and with addition of tyrosine at less bioactive sites of the motilin sequence in order to maintain highly specific binding activity. At present we are continuing the binding study of ^<125>l-motilin to rabbit antral and duodenal smooth muscle cell membranes. Less