Hosey M M, Fields J Z
J Biol Chem. 1981 Jun 25;256(12):6395-9.
Quantitative and qualitative differences in muscarinic cholinergic receptors in embryonic and newborn chick hearts have been found in studies using the radioligand [3H]quinuclidinyl benzilate ([3H]QNB) to label the receptors specifically. In both embryonic and newborn hearts, there appears to be a single class of high affinity muscarinic receptors. However, the number of muscarinic receptors/mg of protein in newborn hearts is significantly greater than in embryonic hearts. Homogenates of newborn and 10-day-old embryonic hearts contain 586 and 278 fmol of muscarinic receptors/mg of protein, respectively. The affinities of the muscarinic cholinergic receptor for [3H]QNB in the two preparations are similar; the KD values as estimated from dissociation and association rate constants are 20 and 12 pM for the newborn and embryonic hearts, respectively. In contrast, marked differences in the properties of the receptors in newborn and embryonic hearts were revealed in studies of inhibition of [3H]QNB binding by cholinergic agonists. The cholinergic agonists acetylcholine and carbamylcholine were approximately 10- to 20-fold more potent in inhibiting [3H]-QNB binding to membranes obtained from embryonic hearts as compared to newborn hearts. Thus, there appear to be developmentally related differences in the affinity of the cardiac muscarinic receptor for agonists but not antagonists.
在使用放射性配体[3H]喹宁环基苯甲酸酯（[3H]QNB）特异性标记受体的研究中，已发现胚胎期和新生期鸡心脏中，毒蕈碱型胆碱能受体存在数量和质量上的差异。在胚胎期和新生期心脏中，似乎都存在单一类型的高亲和力毒蕈碱受体。然而，新生期心脏中每毫克蛋白质中毒蕈碱受体的数量显著多于胚胎期心脏。新生期和10日龄胚胎期心脏的匀浆中，每毫克蛋白质分别含有586和278飞摩尔的毒蕈碱受体。两种制剂中毒蕈碱型胆碱能受体对[3H]QNB的亲和力相似；根据解离和结合速率常数估算，新生期和胚胎期心脏的KD值分别为20和12皮摩尔。相比之下，在胆碱能激动剂对[3H]QNB结合的抑制研究中，发现新生期和胚胎期心脏中受体的性质存在显著差异。与新生期心脏相比，胆碱能激动剂乙酰胆碱和氨甲酰胆碱抑制[3H]-QNB与胚胎期心脏膜结合的效力约高10至20倍。因此，心脏毒蕈碱受体对激动剂而非拮抗剂的亲和力似乎存在与发育相关的差异。
