James M K, Leighton H J
J Pharmacol Exp Ther. 1987 Jan;240(1):138-44.
Guinea pig ilea were incubated in vitro with naloxazone, an irreversible opioid receptor antagonist, in an attempt to determine a dissociation constant (KA) value for the opioid agonist, BW 942C, by the method of partial receptor alkylation. However, concentrations of naloxazone up to 3 X 10(-4) M (120 min incubation-60 min washout) did not depress the maximal response or the slope of the concentration-response curve for BW 942C and, therefore, did not allow calculation of KA value. To analyze the residual activity of BW 942C, tissues were incubated with naloxone for 60 min after naloxazone treatment. Schild analysis of naloxone antagonism after 3 X 10(-6) M naloxazone produced a pKB of 8.0 +/- 0.06 and a slope of 0.88 +/- 0.03, suggesting simple competitive antagonism at a single site. In the absence of naloxazone treatment, naloxone 10(-8) to 10(-5) M antagonized the effects of BW 942C yielding a pKB value and slope of 8.34 +/- 0.08 and 1.0 +/- 0.04, respectively. Schild analysis of naloxone antagonism after 10(-4) M naloxazone yielded a pA2 of 6.23 +/- 0.20 and a slope of 0.55 +/- 0.08. These values were not consistent with simple competitive antagonism at a single receptor site. Modeled curves showed that the data for naloxone antagonism after 10(-4) M naloxazone were consistent with action at two receptor sites with naloxone pKB values of approximately 8.3 (experimentally determined) and approximately 6.0. An alternative explanation of altered affinity for BW 942C and naloxone at a single site produced by naloxazone treatment cannot be excluded.
将豚鼠回肠与不可逆阿片受体拮抗剂纳洛沙宗进行体外孵育，试图通过部分受体烷基化方法确定阿片激动剂BW 942C的解离常数（KA）值。然而，高达3×10⁻⁴ M的纳洛沙宗浓度（孵育120分钟 - 洗脱60分钟）并未降低BW 942C的最大反应或浓度 - 反应曲线的斜率，因此无法计算KA值。为了分析BW 942C的残余活性，在纳洛沙宗处理后，将组织与纳洛酮孵育60分钟。对3×10⁻⁶ M纳洛酮后的纳洛酮拮抗作用进行Schild分析，得出pKB为8.0±0.06，斜率为0.88±0.03，表明在单一部位存在简单竞争性拮抗作用。在未进行纳洛沙宗处理的情况下，10⁻⁸至10⁻⁵ M的纳洛酮拮抗BW 942C的作用，分别产生pKB值和斜率为8.34±0.08和1.0±0.04。对10⁻⁴ M纳洛酮后的纳洛酮拮抗作用进行Schild分析，得出pA2为6.23±0.20，斜率为0.55±0.08。这些值与单一受体部位的简单竞争性拮抗作用不一致。模拟曲线显示，10⁻⁴ M纳洛酮后的纳洛酮拮抗作用数据与在两个受体部位的作用一致，纳洛酮的pKB值约为8.3（实验测定）和约6.0。不能排除纳洛沙宗处理导致单一部位对BW 942C和纳洛酮亲和力改变的另一种解释。
