Tomomasa T, Hyman P E, Hsu C T, Jing J, Snape W J
Department of Pediatrics, Harbor-UCLA Medical Center, Torrance 90509.
Am J Physiol. 1988 May;254(5 Pt 1):G680-6. doi: 10.1152/ajpgi.1988.254.5.G680.
We used binding of [N-methyl-3H]scopolamine ( [3H]-NMS) to tissue homogenates and isometric contraction of muscle strips to characterize perinatal changes in the muscarinic receptor on rabbit gastric smooth muscle. In homogenates from fetal (28 days of gestation), 1-, 3-, and 7-day, 4- and 11-wk-old rabbits, specific binding was saturable and temperature dependent, achieved equilibrium by 10 min at 30 degrees C, and was linearly related to tissue concentration. Specific binding was 80 +/- 2% of total binding at 0.2 nM [3H]NMS. The number of binding sites was 120,000 receptors/cell, maximal during the first week of life compared with the fetus or older animals. Affinity of [3H]NMS was highest in the first week of life (Kd = 345 +/- 24 pM, 1 day old). Age did not affect Hill coefficients or Ki values; secoverine and 4-diphenylacetoxy-N-methylpiperidine methiodide were 50-fold more potent than pirenzepine. In muscle strips, bethanechol stimulated dose-dependent atropine-inhibitable isometric contraction. The doses required for half-maximal contraction were similar in both age groups (5-6 microM), but maximal contraction was fivefold greater in weanlings compared with neonates. Increasing extracellular potassium concentration resulted in similar differences, suggesting that the differences were not receptor related. These results suggest that well-differentiated M2-muscarinic receptors are functional on rabbit gastric smooth muscle during the perinatal period.
我们利用[甲基-3H]东莨菪碱（[3H]-NMS）与组织匀浆的结合以及肌肉条的等长收缩来表征兔胃平滑肌毒蕈碱受体的围产期变化。在来自胎儿（妊娠28天）、出生1天、3天、7天、4周和11周龄兔子的匀浆中，特异性结合是可饱和的且依赖温度，在30℃下10分钟达到平衡，并且与组织浓度呈线性相关。在0.2 nM[3H]NMS时，特异性结合占总结合的80±2%。结合位点的数量为120,000个受体/细胞，与胎儿或年龄较大的动物相比，在出生后的第一周达到最大值。[3H]NMS的亲和力在出生后的第一周最高（Kd = 345±24 pM，1日龄）。年龄不影响希尔系数或Ki值；塞克维林和4-二苯基乙酰氧基-N-甲基哌啶甲碘化物的效力比哌仑西平高50倍。在肌肉条中，氨甲酰甲胆碱刺激剂量依赖性的、阿托品可抑制的等长收缩。两个年龄组达到最大收缩一半所需的剂量相似（5-6 microM），但与新生儿相比，断奶幼兔的最大收缩力大五倍。增加细胞外钾浓度也导致类似的差异，表明这些差异与受体无关。这些结果表明，在围产期，功能良好的M2型毒蕈碱受体在兔胃平滑肌上发挥作用。
