Kouts S, Bennett M R
Neurobiology Research Centre, University of Sydney, New South Wales, Australia.
J Neurocytol. 1990 Jun;19(3):421-31. doi: 10.1007/BF01188408.
The distribution of intracellular acetylcholine receptor was studied by 125I-alpha-bungarotoxin autoradiography as a measure of the local acetylcholine receptor synthesis at junctional and extrajunctional sites in single fibres of the developing anterior latissimus dorsi muscle of the chicken. Large (longer than 2 microns) acetylcholine receptor clusters characteristic of synaptic contacts were localized by immunofluorescence with anti-acetylcholine receptor antibodies. The distance between acetylcholine receptor clusters at embryonic day 11 was 166 +/- 10.5 microns and this distance did not increase despite growth until after 4 days posthatch. The distance between acetylcholine receptor clusters subsequently increased proportionately with the increase in the length of fibres. Intracellular acetylcholine receptors were labelled with 125I-alpha-BGT after first blocking cell-surface acetylcholine receptor with unlabelled alpha-BGT, and treatment with saponin. Intracellular acetylcholine receptor represented about 5-15% of total cellular acetylcholine receptor. Cycloheximide experiments indicated that 80-90% of intracellular acetylcholine receptor examined represented newly synthesized acetylcholine receptor. The spatial distribution of this pool, studied by autoradiography, was determined in relation to the acetylcholine receptor clusters labelled with anti-acetylcholine receptor antibody. Between embryonic day 11 and posthatch day 14 there was a continual increase in intracellular acetylcholine receptor at both junctional and extrajunctional parts of the fibres, but with the greater increases occurring at the junctional regions. Peaks of intracellular acetylcholine receptor became associated with an increasing number of acetylcholine receptor clusters so that by posthatch day 14 there was an 80% correspondence. The accumulation of newly synthesized intracellular acetylcholine receptor under acetylcholine receptor clusters was not the result of the aggregation of nuclei at these sites, suggesting that a higher rate of acetylcholine receptor synthesis per nucleus develops at distributed synaptic sites on anterior latissimus dorsi fibres.
采用¹²⁵I-α-银环蛇毒素放射自显影术研究细胞内乙酰胆碱受体的分布，以此作为鸡发育中的背阔肌单纤维中连接部位和接头外部位局部乙酰胆碱受体合成的指标。用抗乙酰胆碱受体抗体进行免疫荧光定位，确定了突触接触特有的大（长于2微米）乙酰胆碱受体簇。胚胎第11天时乙酰胆碱受体簇之间的距离为166±10.5微米，此距离在孵化后4天之前尽管纤维生长但并未增加。随后，乙酰胆碱受体簇之间的距离随纤维长度的增加而成比例增加。在用未标记的α-银环蛇毒素阻断细胞表面乙酰胆碱受体并用皂角苷处理后，用¹²⁵I-α-BGT标记细胞内乙酰胆碱受体。细胞内乙酰胆碱受体约占细胞总乙酰胆碱受体的5%-15%。放线菌酮实验表明，所检测的细胞内乙酰胆碱受体中80%-90%代表新合成的乙酰胆碱受体。通过放射自显影术研究该库的空间分布，并与用抗乙酰胆碱受体抗体标记的乙酰胆碱受体簇相关联。在胚胎第11天至孵化后第14天期间，纤维的连接部位和接头外部位的细胞内乙酰胆碱受体持续增加，但连接区域增加得更多。细胞内乙酰胆碱受体的峰值与越来越多的乙酰胆碱受体簇相关联，因此到孵化后第14天时，两者的对应率达到80%。乙酰胆碱受体簇下新合成的细胞内乙酰胆碱受体的积累并非这些部位细胞核聚集的结果，这表明背阔肌纤维上分布的突触部位每个细胞核的乙酰胆碱受体合成速率更高。
