Gunst S J, Stropp J Q, Flavahan N A
J Appl Physiol (1985). 1987 Apr;62(4):1755-8. doi: 10.1152/jappl.1987.62.4.1755.
The receptor reserves for acetylcholine, 5-hydroxytryptamine, and histamine in canine tracheal muscle were evaluated. Muscle strips were dissected free of epithelial and connective tissue and suspended for isometric tension recording in modified Krebs-Ringer solution. Dissociation constants for all three agonists were determined by analysis of their concentration-response curves under control conditions and after partial inactivation of receptors by phenoxybenzamine dihydrochloride. The values of KA for acetylcholine, 5-hydroxytryptamine, and histamine were 1.8 X 10(-5) M, 1.35 X 10(-6) M, and 5.0 X 10(-5) M, respectively. Dissociation constants were used to determine receptor occupancy-response relationships. Maximal responses to acetylcholine were obtained by activation of only 4.0 +/- 1.0% of receptors, indicating the presence of a very large receptor-reserve. In contrast, a maximal response to 5-hydroxytryptamine and histamine required activation of 78.0 +/- 11.0 and 87.7 +/- 1.6% of the receptors, respectively, indicating very modest receptor reserves. The differences in receptor-reserve characteristics for these agonists in airway muscle might contribute to the differential effects of inhibitory and facilitory influences on contractions elicited by them.
对犬气管肌肉中乙酰胆碱、5-羟色胺和组胺的受体储备进行了评估。将肌条从上皮组织和结缔组织中分离出来，悬浮于改良的克雷布斯-林格溶液中进行等长张力记录。通过分析在对照条件下以及在盐酸酚苄明使受体部分失活后三种激动剂的浓度-反应曲线，确定了它们的解离常数。乙酰胆碱、5-羟色胺和组胺的KA值分别为1.8×10^(-5)M、1.35×10^(-6)M和5.0×10^(-5)M。解离常数用于确定受体占有率-反应关系。仅激活4.0±1.0%的受体即可获得对乙酰胆碱的最大反应，这表明存在非常大的受体储备。相比之下，对5-羟色胺和组胺的最大反应分别需要激活78.0±11.0%和87.7±1.6%的受体，这表明受体储备非常有限。气道肌肉中这些激动剂的受体储备特征差异可能有助于解释抑制性和促进性影响对它们所引发收缩的不同作用。
