Semyanov A, Godukhin O
Institute of Theoretical and Experimental Biophysics, Russian Academy of Sciences, Pushchino, Moscow Region, 142292, Russia.
Neuropharmacology. 2001;40(2):203-11. doi: 10.1016/s0028-3908(00)00147-7.
We have previously demonstrated that repeated brief increases in extracellular K(+) (K(+)(o)) induce a hyperexcitability in CA1 pyramidal cells that persists for a long time after the final application of K(+) [Neurosci. Lett. 223 (1997) 177; Epilepsy Research (2000) 75]. This epileptiform activity, which was associated with a lasting excitatory postsynaptic potential (EPSP)-spike potentiation, presented some of the characteristic features of traditional in vivo kindling. We have also found that Ca(2+) influx through L-type voltage-sensitive Ca(2+) channels is essential for the development of both in vitro kindling and EPSP-spike potentiation. The aims of this study were to investigate the involvement of ionotropic glutamate receptors, especially those of the NMDA subtype, and the requirement for Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) in these phenomena. Field EPSPs with presynaptic fibre volleys from the stratum radiatum, and population spikes from the stratum pyramidale, were recorded in the CA1 area of rat hippocampal slices in response to electrical stimulation of the Schaffer collateral/commissural fibres. Repeated (three episodes) brief (30 s) increases in extracellular K(+) induced a sustained decrease in the threshold for development of evoked epileptiform discharges (i.e. an in vitro kindling-like state) and a lasting potentiation of the EPSP-spike transfer in CA1 pyramidal neurons (EPSP-spike potentiation). The selective antagonist of NMDA receptors, APV (50 microM), blocked the EPSP-spike potentiation, depressed the induction phase of the in vitro kindling-like state, and blocked the maintenance phase of this state. In contrast to APV, the blockade of AMPA/kainate receptors by CNQX (10 microM) had no effect. Like APV, KN62 (3 microM), a selective membrane permeable inhibitor of CaMKII, blocked the EPSP-spike potentiation and the maintenance phase of the in vitro kindling-like state. Our previous and present results therefore demonstrate that Ca(2+) influxes through L-type voltage-dependent-and NMDA receptor-dependent-Ca(2+) channels contribute differentially to the development of an in vitro kindling-like state, and both induce EPSP-spike potentiation in CA1 hippocampal pyramidal cells in response to repeated brief increases in K(+)(o). It is suggested that these effects of intracellular Ca(2+) on the maintenance phase of the in vitro kindling-like state and EPSP-spike potentiation are mediated by CaMKII-dependent mechanisms.
我们之前已经证明，细胞外钾离子（K(+)(o)）的反复短暂升高会诱导CA1锥体细胞出现超兴奋性，这种超兴奋性在最后一次施加钾离子后会持续很长时间[《神经科学快报》223 (1997) 177；《癫痫研究》(2000) 75]。这种癫痫样活动与持久的兴奋性突触后电位（EPSP）-锋电位增强有关，呈现出传统体内点燃的一些特征。我们还发现，通过L型电压敏感性钙通道的钙离子内流对于体外点燃和EPSP-锋电位增强的发展至关重要。本研究的目的是调查离子型谷氨酸受体，尤其是NMDA亚型受体的参与情况，以及这些现象中对钙/钙调蛋白依赖性蛋白激酶II（CaMKII）的需求。在大鼠海马切片的CA1区域记录来自辐射层的具有突触前纤维群峰电位的场EPSP，以及来自锥体层的群体锋电位，以响应于对Schaffer侧支/联合纤维的电刺激。细胞外钾离子的反复（三次）短暂（30秒）升高诱导诱发癫痫样放电发展阈值的持续降低（即体外点燃样状态）以及CA1锥体神经元中EPSP-锋电位传递的持久增强（EPSP-锋电位增强）。NMDA受体的选择性拮抗剂APV（50 microM）阻断了EPSP-锋电位增强，抑制了体外点燃样状态的诱导期，并阻断了该状态的维持期。与APV相反，CNQX（10 microM）对AMPA/海人藻酸受体的阻断没有作用。与APV一样，CaMKII的选择性膜通透性抑制剂KN62（3 microM）阻断了EPSP-锋电位增强和体外点燃样状态的维持期。因此，我们之前和现在的结果表明，通过L型电压依赖性和NMDA受体依赖性钙通道的钙离子内流对体外点燃样状态的发展有不同的贡献，并且两者都会在响应K(+)(o)的反复短暂升高时诱导CA1海马锥体细胞中的EPSP-锋电位增强。提示细胞内钙离子对体外点燃样状态维持期和EPSP-锋电位增强的这些作用是由CaMKII依赖性机制介导的。
