Nijholt I, Blank T, Liu A, Kügler H, Spiess J
Department of Molecular Neuroendocrinology, Max Planck Institute for Experimental Medicine, Goettingen, Germany.
J Neurochem. 2000 Aug;75(2):749-54. doi: 10.1046/j.1471-4159.2000.0750749.x.
In the present study we investigated the modulation of hypothalamic NMDA receptor-mediated currents by cyclic AMP-dependent protein kinase (PKA) using the two-electrode voltage-clamp technique in Xenopus oocytes injected with rat hypothalamic mRNA. Application of forskolin, which activates PKA by means of cyclic AMP stimulation, caused a transient increase of NMDA-induced currents, whereas the inactive forskolin analogue 1,9-dideoxyforskolin had no effect. Incubation of oocytes with a membrane-permeable analogue of cyclic AMP, 8-bromoadenosine 3',5' -cyclic monophosphate, potentiated NMDA responses even more prominently than with forskolin. NMDA-induced currents recorded from Xenopus oocytes injected with cRNA encoding the NMDA receptor subunits NR1, NR2A, and/or NR2B, mainly found in rat hypothalamus, were not affected by PKA activation but were increased by protein kinase C (PKC) stimulation. It is interesting that inhibition of endogenous protein phosphatase 1 and/or 2A by calyculin A resulted in a similar enhancement of hypothalamic NMDA-induced currents. Preinjection of oocytes with calyculin A impeded the PKA- but not the PKC-mediated potentiation of hypothalamic NMDA-induced currents. We propose the involvement of an additional third messenger in the PKA effect, which acts most likely via the inhibition of tonically active protein phosphatase 1 and/or 2A.
在本研究中，我们运用双电极电压钳技术，在注射了大鼠下丘脑mRNA的非洲爪蟾卵母细胞中，研究了环磷酸腺苷依赖性蛋白激酶（PKA）对下丘脑N-甲基-D-天冬氨酸（NMDA）受体介导电流的调节作用。通过环磷酸腺苷刺激激活PKA的福斯可林的应用，导致NMDA诱导电流短暂增加，而无活性的福斯可林类似物1,9-二脱氧福斯可林则无作用。用膜通透性环磷酸腺苷类似物8-溴腺苷3',5'-环磷酸单酯孵育卵母细胞，比福斯可林更显著地增强了NMDA反应。从注射了编码主要在大鼠下丘脑中发现的NMDA受体亚基NR1、NR2A和/或NR2B的cRNA的非洲爪蟾卵母细胞中记录到的NMDA诱导电流，不受PKA激活的影响，但受蛋白激酶C（PKC）刺激的增加。有趣的是，毛喉素对内源性蛋白磷酸酶1和/或2A的抑制导致下丘脑NMDA诱导电流有类似的增强。用毛喉素预先注射卵母细胞会阻碍PKA介导的但不阻碍PKC介导的下丘脑NMDA诱导电流的增强。我们提出在PKA效应中有另一种第三信使的参与，它最有可能通过抑制持续活跃的蛋白磷酸酶1和/或2A起作用。
