Department of Pharmacology, Wakayama Medical University, Wakayama, Japan.
Biol Pharm Bull. 2010;33(6):1011-4. doi: 10.1248/bpb.33.1011.
We have examined the involvement of serine/threonine protein phosphatase (PP) sensitive to okadaic acid (OA) in the antinociceptive effect of morphine in mice. The present study was performed to elucidate subcellular distribution and activity of OA-sensitive PPs in the brain when mice exposed to morphine. Subcutaneous administration of morphine (5 mg/kg) produced the antinociceptive effect with the maximum 30 min after its administration, evaluated by tail-pinch test. The antinociception was accompanied by an increment of activity in OA-sensitive PPs in the membrane fraction prepared from the whole brain of mice treated with morphine: The temporal profile of the morphine-induced increment of OA-sensitive PP activity was consistent with that of antinociceptive effects of morphine. The morphine-induced increase in OA-sensitive PP activity was dependent on the dose and attenuated by the concurrent administration of naloxone (1 mg/kg). To identify the subtype of OA-sensitive PPs in morphine-enhanced activity, we examined the level of PP2A and PP5, OA-sensitive PPs, in the subcellular fraction prepared from the whole brain of mice receiving morphine. Western blot revealed that morphine elicited the significant increase in the level of PP5, but not PP2A, in the membrane fraction, with the same peak time for the increment of PP5 as the antinociception. No significant change was observed in the level of OA-sensitive PPs in the cytosolic fraction at any examined time after morphine. These results suggest that the translocation of PP5 to the membrane fraction is, at least in part, involved in the antinociceptive effect of morphine in mice.
我们研究了丝氨酸/苏氨酸蛋白磷酸酶（PP）对冈田酸（OA）的敏感性是否参与了吗啡在小鼠中的镇痛作用。本研究旨在阐明吗啡暴露时脑内 OA 敏感 PP 的亚细胞分布和活性。皮下给予吗啡（5mg/kg）可通过尾部压痛试验在给药后 30 分钟内产生最大的镇痛作用。镇痛作用伴随着 OA 敏感 PP 在吗啡处理的小鼠全脑膜部分中活性的增加：吗啡诱导的 OA 敏感 PP 活性增加的时间进程与吗啡镇痛作用的时间进程一致。吗啡诱导的 OA 敏感 PP 活性增加依赖于剂量，并被纳洛酮（1mg/kg）的同时给药所减弱。为了确定吗啡增强活性中 OA 敏感 PP 的亚型，我们检查了接受吗啡的小鼠全脑亚细胞部分中 PP2A 和 PP5（OA 敏感 PP）的水平。Western blot 显示，吗啡在膜部分引起 PP5 水平的显著增加，但 PP2A 没有增加，PP5 的增加与镇痛作用具有相同的峰值时间。在吗啡后任何检查时间，胞质部分中 OA 敏感 PP 的水平均未观察到明显变化。这些结果表明，PP5 向膜部分的易位至少部分参与了吗啡在小鼠中的镇痛作用。
