Van Assche G, Depoortere I, Peeters T L
Gut Hormone Laboratory, University of Leuven, Gasthuisberg, Belgium.
Regul Pept. 1998 Oct 16;77(1-3):89-94. doi: 10.1016/s0167-0115(98)00104-9.
Motilin stimulates gastrointestinal motility, but in vitro studies reveal a direct smooth muscle effect, whereas in vivo studies reveal a neurally mediated effect. The aim of the present study was to determine if motilin binds to microsomes (smooth muscle) and/or synaptosomes (neurons).
Subcellular fractions were prepared from tissue of rabbit gastric antrum and colon by differential centrifugation and density gradient centrifugation and characterized by determining motilin binding and the presence of membrane markers.
The purified microsomal fraction, enriched in the smooth muscle marker 5'-nucleotidase, was found to have the highest specific motilin binding in both antrum and colon. In the antrum, but not in the colon, the mitochondrial fraction also showed enrichment of [3H]-saxitoxin binding (marker for synaptosomes) and motilin binding, although the latter was much lower than in the microsomal fraction. Two receptor binding sites were characterized in both the antral mitochondrial/synaptosomal and colonic microsomal fraction (antrum: pKd,1 9.89+/-0.19, pKd,2 8.18+/-0.11, colon: pKd,1 9.72+/-0.31, pKd,2 8.39+/-0.58).
Motilin binding is predominantly associated with smooth muscle membranes in both antrum and colon of the rabbit. In both organs two motilin binding sites are present with comparable affinities, but the density in the colon is much higher for both sites. Whether they represent neural and smooth muscle receptors will require studies with isolated smooth muscle cells and neurons.
胃动素可刺激胃肠蠕动，但体外研究显示其对平滑肌有直接作用，而体内研究则显示其作用是通过神经介导的。本研究旨在确定胃动素是否与微粒体（平滑肌）和/或突触体（神经元）结合。
通过差速离心和密度梯度离心从兔胃窦和结肠组织中制备亚细胞组分，并通过测定胃动素结合情况和膜标志物的存在来进行表征。
富含平滑肌标志物5'-核苷酸酶的纯化微粒体组分在胃窦和结肠中均具有最高的特异性胃动素结合能力。在胃窦中，线粒体组分也显示出[3H]-石房蛤毒素结合（突触体标志物）和胃动素结合增加，尽管后者远低于微粒体组分，但在结肠中未出现这种情况。在胃窦线粒体/突触体组分和结肠微粒体组分中均鉴定出两个受体结合位点（胃窦：pKd,1 9.89±0.19，pKd,2 8.18±0.11；结肠：pKd,1 9.72±0.31，pKd,2 8.39±0.58）。
在兔的胃窦和结肠中，胃动素结合主要与平滑肌膜相关。在这两个器官中均存在两个具有相当亲和力的胃动素结合位点，但结肠中两个位点的密度均更高。它们是否代表神经和平滑肌受体，还需要对分离的平滑肌细胞和神经元进行研究。
