Fuder H, Rink D, Muscholl E
Naunyn Schmiedebergs Arch Pharmacol. 1982 Feb;318(3):210-9. doi: 10.1007/BF00500482.
Rat isolated hearts with the sympathetic nerves attached were perfused with (-)-3H-noradrenaline in order to label the storage vesicles of the adrenergic nerves. Release was induced either by electrical stimulation of the nerves (3 Hz, 1 min) or by perfusion with high K+ solution (54 mM). The overflow of 3H-noradrenaline and its metabolites was determined by liquid scintillation counting after separation of the compounds by column chromatography. The experimental conditions ensured a minor contribution of 3H-metabolites to the evoked total tritium overflow. The release of 3H-noradrenaline evoked by nerve stimulation or high K+ solution was decreased in the presence of the muscarinic agonist, methacholine, N-methylatropine reversed the inhibition completely. Thus, the rat heart contains inhibitory muscarine receptors modulating noradrenaline release from adrenergic nerve fibres. In order to compare the presynaptic muscarine receptors with postsynaptic muscarine receptors in one and the same organ, the pA2 values of N-methylatropine and pirenzepine at both of these sites were measured. The antagonism of methacholine-induced inhibition of 3H-noradrenaline overflow was determined as the presynaptic parameter. pA2 values of 9.61 for N-methylatropine and 6.63 for pirenzepine were found. The methacholine-induced inhibition of the atrial tension development of isolated left rat atria paced at 2Hz was measured as a postsynaptic parameter. pA2 values of 9.90 for N-methylatropine and 6.69 for pirenzepine were found. The postsynaptic pA2 values did not differ from the presynaptic affinity constants indicating that neither substance revealed differences in structure between neuronal and myocardial muscarine receptors in the rat heart.
将带有交感神经的大鼠离体心脏用（-）-3H-去甲肾上腺素灌注，以便标记肾上腺素能神经的储存囊泡。通过电刺激神经（3Hz，1分钟）或用高钾溶液（54mM）灌注来诱导释放。在通过柱色谱分离化合物后，通过液体闪烁计数法测定3H-去甲肾上腺素及其代谢产物的溢出量。实验条件确保了3H-代谢产物对诱发的总氚溢出量的贡献较小。在毒蕈碱激动剂乙酰甲胆碱存在的情况下，神经刺激或高钾溶液诱发的3H-去甲肾上腺素释放减少，N-甲基阿托品可完全逆转这种抑制作用。因此，大鼠心脏含有调节肾上腺素能神经纤维去甲肾上腺素释放的抑制性毒蕈碱受体。为了比较同一器官中突触前毒蕈碱受体和突触后毒蕈碱受体，测量了N-甲基阿托品和哌仑西平在这两个位点的pA2值。将乙酰甲胆碱诱导的3H-去甲肾上腺素溢出抑制的拮抗作用确定为突触前参数。发现N-甲基阿托品的pA2值为9.61，哌仑西平的pA2值为6.63。将乙酰甲胆碱诱导的2Hz起搏的离体大鼠左心房张力发展的抑制作用作为突触后参数进行测量。发现N-甲基阿托品的pA2值为9.90，哌仑西平的pA2值为6.69。突触后pA2值与突触前亲和力常数没有差异，表明这两种物质在大鼠心脏的神经元和心肌毒蕈碱受体之间均未显示出结构差异。
