ACh对大鼠皮层体感区神经元延迟整流钾电流的抑制作用

Inhibition of ACh on the delayed rectifier-like potassium current in acutely isolated cerebral cortical neurons of rats

利用全细胞膜片钳技术研究乙酰胆碱(acetylcholine,ACh)对大鼠皮层体感区神经元延迟整流钾电流(IK)的调制作用。结果表明:(1)ACh(0．1、1、10、100 μmol/L)对大鼠皮层体感区神经元IK有抑制作用,并具有剂量依赖性关系(P<0．01)。 (2)ACh可使IK激活曲线的斜率变大,并使激活曲线向超极化方向移动。IK激活曲线的半数激活电压(V1/12)和斜率因子(k)分别由给药前的(-41．8±9．7)mV和(30．7±7．2)mV变为给药后的(-122．4±38．6)mV和(42．4±7．0)mV。(3)100 μmol/L的N受体拮抗剂筒箭毒碱(tubocurarine)可减弱ACh对IK的抑制作用,在指令电压+60 mV时tubocurarine+ACh组的IK幅度下降了(16．9± 13．8)％(n=8),与10 μmol/L ACh组引起的(36．5±7．8)％的IK下降幅度相比,有极显著差异(P<0．01)。10 μmol/L的M1受体拮抗剂哌仑西平(pirenzepin)拮抗ACh对IK的抑制作用不明显(n=7,P>0．05);而10 μmol/L的M3受体拮抗剂4-DAMP可部分拮抗ACh对IK的抑制作用,并且4-DAMP+ACh组使IK的电流值下降了(26．8±4．7)％(n=6),与ACh组引起的IK电流下降相比,有显著差异(P<0．05)。(4)蛋白激酶C(protein kinase C,PKC)阻断剂chelerythrine拮抗ACh对IK的抑制作用,PKC激动剂PDBu可增强ACh对IK的抑制作用(P<0．05)。综上所述,ACh对人鼠皮层体感区神经元IK的抑制作用主要是通过烟碱受体(nAChRs)和M3受体介导,并经过PKC信号途径。

The modulation of ACh on delayed rectifier-like potassium currents （Ik） was studied in freshly dissociated cerebral cortical neurons using the whole-cell patch-clamp technique. Wistar rats between 10- and 14-day old of both sexes were used. After rats were decapitated, their brains were quickly removed, iced, and then manually cut into 400μm slices. Slices were then incubated for 0.5 h at 32℃ in a buffered artificial cerebrospinal fluid （ACSF） bubbled with 95% 02, 5% CO2. Slices were then removed into buffered ACSF containing protease （0.5 mg/ml） at 32℃. After 30 rain of enzyme digestion, tissue was rinsed three times in the buffered saline. Then the enzyme-treated slices were mechanically dissociated with a graded series of fire-polished Pasteur pipettes. The cell suspension was then plated into a 35 mm dish and placed on the stage of a Olympus inverted microscope. For whole-cell recordings of currents, standard voltage-clamp techniques were used. Neurons were held at -80 mV, and the IK was evoked by 2 000 ms depolarizing voltage commands to potential between -40 mV and ＋60 mV in 10 mV steps applied at a frequency of 0.5 Hz. It was found that the inhibitory effect of ACh （0.1, 1, 10, 100μmol/L） on IK was dose-dependent. It was also found that ACh affected the activation process of IK significantly, i.e., the activation curve of IK was characterized by half-activation potential of （-41.8±9.7） mV and a slope factor of （30.7±7.2） mV in the cortical neurons and they were changed to （-122.4±38.6） mV and （42.4±7.0） mV, respectively, after giving ACh （10μmol/L）. Tubocurarine （100μmol/L） antagonized the inhibitory effect of ACh on IK, and the drop of currents varied from the control value of （36.5±7.8）% to （16.9±13.8）% （n=8, P〈0.01）. 4-DAMP （10μmol/L） blocked the inhibitory effect of ACh on IK, and the currents reduced from the control value of （36.5±7.8）% to （26.8±4.7）% （n=6, P〈0.05）. Pirenzepin did not antagonize the inhibition ofACh on IK （n=7, P〉0.05）. Chelerythrine （20μmol/L） blocked the inhibitory effect of ACh on IK and the currents reduced from the control value of （36.5±7.8）% to （11.7±17.3）% （n=6, P〈0.05）. On the contrary, PDBu （10μmol/L） strengthened the inhibition of ACh on IK and the drop of currents changed from the control value of （36.5±7.8）% to （59.2±14.0）% （n=5, P〈0.05）. PDBu abolished the antagonism of chelerythrine on ACh in cortical neurons. It is suggested that the ACh-induced depolarization of neurons in the cortex is attributed to the inhibition of IK that is most likely evoked by the activation of nicotinic ACh receptors and muscarinic M3 receptor via protein kinase C （PKC） signal transduction pathway.