Ladera Carolina, Martín Ricardo, Bartolomé-Martín David, Torres Magdalena, Sánchez-Prieto José
Departamento de Bioquímica, Facultad de Veterinaria, Universidad Complutense, Madrid, Spain.
Eur J Neurosci. 2009 Mar;29(6):1131-40. doi: 10.1111/j.1460-9568.2009.06675.x.
N-type and P/Q-type Ca(2+) channels support glutamate release at central synapses. To determine whether the glutamate release mediated by these channels exhibits distinct properties, we have isolated each release component in cerebrocortical nerve terminals from wild-type mice by specifically blocking N-type Ca(2+) channels with omega-conotoxin-GVIA and P/Q-type Ca(2+) channels with omega-agatoxin-IVA. In addition, we have determined the release properties at terminals from mice lacking the alpha(1B) subunit of N-type channels (Ca(v) 2.2) to test the possibility that P/Q-type channels can compensate for the loss of N-type Ca(2+) channels. We recently demonstrated that, while evoked glutamate release depends on P/Q- and N-type channels in wild-type nerve terminals, only P/Q-type channels participate in these knockout mice. Moreover, in nerve terminals expressing solely P/Q-type channels, metabotropic glutamate receptor 7 (mGluR7) fails to inhibit the evoked Ca(2+) influx and glutamate release. Here, we show that the failure of mGluR7 to modulate evoked glutamate release is not due to a lack of receptors, as nerve terminals from mice lacking N-type Ca(2+) channels express mGluR7. Indeed, we show that other receptor responses, such as the inhibition of forskolin-induced release, are preserved in these knockout mice. N-type channels are more loosely coupled to release than P/Q-type channels in nerve terminals from wild-type mice, as reflected by the tighter coupling of release in knockout nerve terminals. We conclude that the glutamate release supported by N- and P/Q-type channels exhibits distinct properties, and that P/Q-type channels cannot fully compensate for the loss of N-type channels.
N型和P/Q型钙离子通道在中枢突触处支持谷氨酸释放。为了确定由这些通道介导的谷氨酸释放是否具有不同特性，我们通过用ω-芋螺毒素-GVIA特异性阻断N型钙离子通道以及用ω-阿加毒素-IVA特异性阻断P/Q型钙离子通道，从野生型小鼠的大脑皮质神经末梢中分离出了每种释放成分。此外，我们还测定了缺乏N型通道α(1B)亚基（Ca(v) 2.2）的小鼠神经末梢的释放特性，以测试P/Q型通道能否补偿N型钙离子通道缺失的可能性。我们最近证明，虽然野生型神经末梢中诱发的谷氨酸释放依赖于P/Q型和N型通道，但在这些基因敲除小鼠中只有P/Q型通道参与其中。此外，在仅表达P/Q型通道的神经末梢中，代谢型谷氨酸受体7（mGluR7）无法抑制诱发的钙离子内流和谷氨酸释放。在此，我们表明mGluR7无法调节诱发的谷氨酸释放并非由于缺乏受体，因为缺乏N型钙离子通道的小鼠的神经末梢表达mGluR7。事实上，我们表明在这些基因敲除小鼠中其他受体反应，如对福斯高林诱导释放的抑制作用，是保留的。在野生型小鼠的神经末梢中，N型通道与释放的偶联比P/Q型通道更松散，这在基因敲除神经末梢中释放的更紧密偶联中得到体现。我们得出结论，N型和P/Q型通道支持的谷氨酸释放具有不同特性，并且P/Q型通道不能完全补偿N型通道的缺失。
