Chen H X, Otmakhov N, Strack S, Colbran R J, Lisman J E
Volen Center for Complex Systems, Brandeis University, Waltham, Massachusetts 02454, USA.
J Neurophysiol. 2001 Apr;85(4):1368-76. doi: 10.1152/jn.2001.85.4.1368.
Calcium/calmodulin-dependent protein kinase II (CaMKII) is concentrated in the postsynaptic density (PSD) and plays an important role in the induction of long-term potentiation (LTP). Because this kinase is persistently activated after the induction, its activity could also be important for LTP maintenance. Experimental tests of this hypothesis, however, have given conflicting results. In this paper we further explore the role of postsynaptic CaMKII in induction and maintenance of LTP. Postsynaptic application of a CaMKII inhibitor [autocamtide-3 derived peptide inhibitor (AC3-I), 2 mM] blocked LTP induction but had no detectable affect on N-methyl-D-aspartate (NMDA)-mediated synaptic transmission, indicating that the primary function of CaMKII in LTP is downstream from NMDA channel function. We next explored various methodological factors that could account for conflicting results on the effect of CaMKII inhibitors on LTP maintenance. In contrast to our previous work, we now carried out experiments at higher temperature (33 degrees C), used slices from adult animals, and induced LTP using a tetanic stimulation. However, we still found that LTP maintenance was not affected by postsynaptic application of AC3-I. Furthermore the inhibitor did not block LTP maintenance under conditions designed to enhance the Ca(2+)-dependent activity of protein phosphatases 1 and 2B (elevated Ca(2+), calmodulin, and an inhibitor of protein kinase A). We also tested the possibility that CaMKII inhibitor might not be able to affect CaMKII once it was inserted into the PSD. In whole-brain extracts, AC3-I blocked autophosphorylation of both soluble and particulate/PSD CaMKII with similar potencies although the potency of the inhibitor toward other CaMKII substrates varied. Thus we were unable to demonstrate a functional role of persistent Ca(2+)-independent CaMKII activity in LTP maintenance. Possible explanations of the data are discussed.
钙/钙调蛋白依赖性蛋白激酶II（CaMKII）集中于突触后致密区（PSD），并在长时程增强（LTP）的诱导中发挥重要作用。由于该激酶在诱导后持续被激活，其活性对于LTP的维持可能也很重要。然而，对这一假说的实验测试结果相互矛盾。在本文中，我们进一步探讨突触后CaMKII在LTP诱导和维持中的作用。突触后应用CaMKII抑制剂[自抑制肽-3衍生肽抑制剂（AC3-I），2 mM]可阻断LTP的诱导，但对N-甲基-D-天冬氨酸（NMDA）介导的突触传递没有可检测到的影响，这表明CaMKII在LTP中的主要功能位于NMDA通道功能的下游。接下来，我们探讨了各种可能导致CaMKII抑制剂对LTP维持作用结果相互矛盾的方法学因素。与我们之前的工作不同，我们现在在较高温度（33摄氏度）下进行实验，使用成年动物的脑片，并通过强直刺激诱导LTP。然而，我们仍然发现突触后应用AC3-I并不影响LTP的维持。此外，在旨在增强蛋白磷酸酶1和2B的钙依赖性活性（升高的钙离子、钙调蛋白和蛋白激酶A抑制剂）的条件下，该抑制剂也不阻断LTP的维持。我们还测试了CaMKII抑制剂一旦插入PSD后可能无法影响CaMKII的可能性。在全脑提取物中，AC3-I以相似的效力阻断可溶性和颗粒性/PSD CaMKII的自磷酸化，尽管该抑制剂对其他CaMKII底物的效力有所不同。因此，我们无法证明持续的非钙依赖性CaMKII活性在LTP维持中的功能作用。文中讨论了这些数据的可能解释。
