Garland L G, Marrion N V, Martin G R
Naunyn Schmiedebergs Arch Pharmacol. 1981 Dec;318(2):88-93. doi: 10.1007/BF00508831.
Tracheal rings isolated from male guinea-pigs and incubated in Krebs' solution at 37 degrees C O-methylated 3H-(+/-)-isoprenaline by a saturable, high affinity mechanism. 1. With 3H-isoprenaline at 1 mumol . 1-1, O-methyl 3H-(+/-)isoprenaline (3H-OMI) appeared in the tissue with a half-time for approach to steady state of approximately 10 min and was measured in the incubation medium after about 5 min, its concentration increasing linearly thereafter. With 3H-isoprenaline concentrations ranging from 1 to 200 mumol . 1-1, the total formation of 3H-OMI (estimated from that contained in the tissue and the medium) was maintained at steady state rates for up to 60 min, after initial lag times of between 1 and 3 min. O-methylation obeyed Michaelis-Menten saturation kinetics; Km = 6.14 +/- 0.13 mumol . 1-1, Vmax = 0.31 +/- 0.01 nmol . g-1 . min-1. 2. The catechol-O-methyl transferase (COMT) inhibitor U-O521 and the extraneuronal uptake inhibitor corticosterone both reduced O-methylation of 3H-isoprenaline (0.1 mumol . 1-1) by tracheal rings. However, U-O521 was fully inhibitory (IC50 = 2.6 mumol . 1-1), but corticosterone inhibited by only 46% at concentrations up to 1 mmol . 1-1. 3. The O-methylating activity of the "smooth muscle-rich" component of the trachea was approximately three-times greater than for complete tracheal rings. However, considerable activity was also associated with "cartilage-rich", "smooth muscle-poor" sections. This activity did not seem to be associated with endothelial cells. 4. Histamine strongly inhibited O-methylation (IC50 = 30 mumol . 1-1), but two other contractile agonists, 5-hydroxytryptamine and bethanechol, were weakly active and inactive, respectively.
从雄性豚鼠分离出气管环，在37℃的克雷布斯溶液中孵育，气管环通过一种可饱和的高亲和力机制对3H-(+/-)-异丙肾上腺素进行O-甲基化。1. 当3H-异丙肾上腺素浓度为1 μmol·L-1时，O-甲基3H-(+/-)异丙肾上腺素（3H-OMI）在组织中出现，达到稳态的半衰期约为10分钟，约5分钟后在孵育培养基中进行测量，此后其浓度呈线性增加。当3H-异丙肾上腺素浓度在1至200 μmol·L-1范围内时，3H-OMI的总生成量（根据组织和培养基中的含量估算）在最初1至3分钟的滞后时间后，以稳态速率维持长达60分钟。O-甲基化遵循米氏饱和动力学；Km = 6.14±0.13 μmol·L-1，Vmax = 0.31±0.01 nmol·g-1·min-1。2. 儿茶酚-O-甲基转移酶（COMT）抑制剂U-O521和非神经元摄取抑制剂皮质酮均降低了气管环对3H-异丙肾上腺素（0.1 μmol·L-1）的O-甲基化。然而，U-O521具有完全抑制作用（IC50 = 2.6 μmol·L-1），但皮质酮在浓度高达1 mmol·L-1时仅抑制46%。3. 气管“富含平滑肌”部分的O-甲基化活性约为完整气管环的三倍。然而，“富含软骨”、“平滑肌较少”的部分也具有相当的活性。这种活性似乎与内皮细胞无关。4. 组胺强烈抑制O-甲基化（IC50 = 30 μmol·L-1），但另外两种收缩激动剂5-羟色胺和氨甲酰甲胆碱分别具有微弱活性和无活性。
