Inhibition of N- and P/Q-type calcium channels by postsynaptic GABAB receptor activation in rat supraoptic neurones
Inhibition of N- and P/Q-type calcium channels by postsynaptic GABAB receptor activation in rat supraoptic neurones
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DOI：
10.1111/j.1469-7793.1998.371bn.x
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发表时间：
1998-06-01
影响因子：
5.5
通讯作者：
Yamashita, H
中科院分区：
文献类型：
--
作者：
Harayama, N;Shibuya, I;Yamashita, H
1.利用膜片钳技术的全细胞结构测量了离解大鼠视上核（SON）神经元的电压依赖性Ca2+电流，以检查GABA(B)受体激活对SON大细胞神经元的直接突触后效应。选择性GABA激动剂巴氯芬以剂量依赖的方式可逆地抑制电压依赖性Ca2+电流，这些电流由保持电位-80 mV到去极化电位的电压阶跃引起。巴氯芬抑制Ca2+电流的ED50为1.4 × 10(-6) m。巴氯芬不抑制电压从-120到-40 mv引起的低阈值Ca2+电流。当选择性GABA(B)拮抗剂CGP 35348和CGP 55845A与巴氯芬的摩尔比分别为10:1和001:1时，巴氯芬对高阈值Ca2+电流的抑制作用被CGP 35348和CGP 55845A迅速完全逆转。它也被反向的预脉冲+150毫伏持续100毫秒。当细胞用百日咳毒素预处理超过20小时或用n -乙基马来酰亚胺预处理2分钟时，Ca2+电流的抑制被消除。当GDP beta S被包括在移液器中时，它也被废除了。当GTP γ X被包括在膜片移液器中时，巴氯芬对Ca2+电流产生不可逆的抑制作用，这种抑制作用再次被预脉冲程序逆转。巴氯芬（10(-5)M）对N-型、P/Q-型、L-型和r -型Ca2+通道的抑制作用分别占Ca2+总电流的24.1%、10.5、3.1和3.6%。只有N-型和P/ q型的抑制作用显著。这些结果表明，GABA受体存在于SON大细胞神经元的突触后位点，并通过百日咳毒素敏感的G蛋白介导对N-型和P/ q型电压依赖性Ca2+通道的选择性抑制作用，这种抑制机制可能在GABA神经元对SON神经元的调节中起作用。
1.Voltage-dependent Ca2+ currents of dissociated rat supraoptic nucleus (SON) neurones were measured using the whole-cell configuration of the patch-clamp technique to examine direct postsynaptic effects of GABA(B) receptor activation on SON magnocellular neurones.2. The selective GABA, agonist baclofen reversibly inhibited voltage-dependent Ca2+ currents elicited by voltage steps from a holding potential of -80 mV to depolarized potentials in a dose-dependent manner. The ED50 of baclofen for inhibiting Ca2+ currents was 1.4 x 10(-6) M. Baclofen did not inhibit low threshold Ca2+ currents elicited by voltage steps from -120 to -40 mV.3. Inhibition of high threshold Ca2+ currents by baclofen was rapidly and completely reversed by the selective GABA(B) antagonists, CGP 35348 and CGP 55845A, when the antagonists were added at the molar ratio vs. baclofen of 10:1 and 001:1, respectively. It was also reversed by a prepulse to +150 mV lasting for 100 ms.4. The inhibition of Ca2+ currents was abolished when the cells were pretreated with pertussis toxin for longer than 20 h or with N-ethylmaleimide for 2 min. It was also abolished when GDP beta S was included in the patch pipette. When GTP gamma X was included in the patch pipette, baclofen produced irreversible inhibition of Ca2+ currents and this inhibition was again reversed by the prepulse procedure.5. The inhibition of N-, P/Q-, L- and R-type Ca2+ channels by baclofen (10(-5) M) was 24.1, 10.5, 3.1 and 3.6%, respectively, of the total Ca2+ currents. Only the inhibition of N- and P/Q-types was significant.6. These results suggest that GABA, receptors exist in the postsynaptic sites of the SON magnocellular neurones and mediate selective inhibitory actions on voltage-dependent Ca2+ channels of N- and P/Q-types via pertussis toxin-sensitive G proteins, and that such inhibitory mechanisms may play a role in the regulation of SON neurones by the GABA neurones.