Fukunaga K, Muller D, Miyamoto E
Department of Pharmacology, Kumamoto University School of Medicine, Japan.
Neurochem Int. 1996 Apr;28(4):343-58. doi: 10.1016/0197-0186(95)00097-6.
The observation that autophosphorylation converts CaM kinase II from the Ca(2+)-dependent form to the Ca(2+)-independent form has led to speculation that the formation of the Ca(2+)-independent form of the enzyme could encode frequency of synaptic usage and serve as a molecular explanation of "memory". In cultured rat hippocampal neurons, glutamate elevated the Ca(2+)-independent activity of CaM kinase II through autophosphorylation, and this response was blocked by an NMDA receptor antagonist, D-2-amino-5-phosphonopentanoate (AP5). In addition, we confirmed that high, but not low frequency stimulation, applied to two groups of CA1 afferents in the rat hippocampus, resulted in LTP induction with concomitant long-lasting increases in Ca(2+)-independent and total activities of CaM kinase II. In experiments with 32P-labeled hippocampal slices, the LTP induction in the CA1 region was associated with increases in autophosphorylation of both alpha and beta subunits of CaM kinase II 1 h after LTP induction. Significant increases in phosphorylation of endogenous CaM kinase II substrates, synapsin I and microtubule-associated protein 2 (MAP2), which are originally located in presynaptic and postsynaptic regions, respectively, were also observed in the same slice. All these changes were prevented when high frequency stimulation was applied in the presence of AP5 or a calmodulin antagonist, calmidazolium. Furthermore, in vitro phosphorylation of the AMPA receptor by CaM kinase II was reported in the postsynaptic density and infusion of the constitutively active CaM kinase II into the hippocampal neurons enhanced kainate-induced response. These results support the idea that CaM kinase II contributes to the induction of hippocampal LTP in both postsynaptic and presynaptic regions through phosphorylation of target proteins such as the AMPA receptor, MAP2 and synapsin I.
自身磷酸化可使钙调蛋白激酶II从钙依赖型转变为钙非依赖型，这一发现引发了人们的猜测：酶的钙非依赖型的形成可能编码突触使用频率，并作为“记忆”的分子解释。在培养的大鼠海马神经元中，谷氨酸通过自身磷酸化提高了钙调蛋白激酶II的钙非依赖型活性，而这种反应被NMDA受体拮抗剂D-2-氨基-5-磷酸戊酸（AP5）阻断。此外，我们证实，对大鼠海马中的两组CA1传入纤维施加高频而非低频刺激，会导致长时程增强（LTP）的诱导，并伴随着钙调蛋白激酶II的钙非依赖型活性和总活性的持久增加。在用32P标记海马切片的实验中，LTP诱导后1小时，CA1区的LTP诱导与钙调蛋白激酶II的α和β亚基的自身磷酸化增加有关。在同一切片中还观察到内源性钙调蛋白激酶II底物突触素I和微管相关蛋白2（MAP2）的磷酸化显著增加，它们最初分别位于突触前和突触后区域。当在AP5或钙调蛋白拮抗剂氯咪达唑存在的情况下施加高频刺激时，所有这些变化都被阻止。此外，有报道称钙调蛋白激酶II在突触后致密区对AMPA受体进行体外磷酸化，将组成型活性钙调蛋白激酶II注入海马神经元可增强海人藻酸诱导的反应。这些结果支持了这样一种观点，即钙调蛋白激酶II通过对AMPA受体、MAP2和突触素I等靶蛋白的磷酸化，在突触后和突触前区域都有助于海马LTP的诱导。
