MECHANISM OF ACTION OF ACETYLCHOLINE ON CALCIUM CURRENT IN SINGLE CELLS FROM FROG VENTRICLE
MECHANISM OF ACTION OF ACETYLCHOLINE ON CALCIUM CURRENT IN SINGLE CELLS FROM FROG VENTRICLE
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DOI：
10.1113/jphysiol.1986.sp016148
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发表时间：
1986-07-01
影响因子：
5.5
通讯作者：
HARTZELL, HC
中科院分区：
文献类型：
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作者：
FISCHMEISTER, R;HARTZELL, HC
1.用全细胞膜片钳技术测定了蛙心室单细胞的钙电流（伊卡），用细胞内（120 mM）和细胞外（20 mM）铯阻断蛙心室单细胞的钾电流。0.5 mM-Cd可完全阻断由去极化电压阶跃（-80 mV）引起的内向电流。2.电压钳的质量使用单个细胞上的两个贴片电极进行评估。一个电极用于电压钳模式以测量膜电流，另一个电极用于电流钳模式以测量膜电位。在长达210 μ m的细胞中，大至2nA的Ca电流被很好地钳制。3.乙酰胆碱（ACh）在不存在β-半胱氨酸的情况下对伊卡没有影响。肾上腺素能刺激，但降低到控制水平，异丙肾上腺素升高伊卡。纳摩尔浓度的ACh能够显著降低由2 μ M-异丙肾上腺素升高的伊卡。4. ACh对I-V曲线的形状、再激活（从失活中恢复）或伊卡失活没有影响。尽管异丙肾上腺素使伊卡平均增加6.5倍，但它对I-V曲线的形状或在负至+40 mV的测试电位下的失活没有影响。然而，异丙肾上腺素使半激活时间从对照值120 ± 100减慢。10 ms（平均值±.标准差）至153 .+-。-80 mV时为12 ms。5.使用两个贴片电极研究了环AMP对伊卡的影响，其中一个电极填充有环AMP。在移液管中使用5 μ M-环AMP时观察到环AMP的最大效应。在用第二个电极破坏贴片后几分钟记录最大伊卡。在除去含环AMP的电极后，伊卡在约10分钟后下降到对照水平。6.第六章贴片电极中的5 μ M-环AMP使伊卡平均增加6.9倍，但对I-V曲线的形状或失活没有影响。环AMP对再活化具有减慢作用（半再活化时间= 155 ± 100 μ g/ml）。24 ms），与异丙肾上腺素相似。7. ACh（1-10 μ M）不降低用环AMP（移液管中0.1-20 μ M-环AMP）升高的伊卡。在移液管中具有低浓度的环AMP（0.1 μ M）时，异丙肾上腺素增加伊卡，但在移液管中具有5 μ M-环AMP时，异丙肾上腺素不能进一步增加伊卡。8.这些结果表明，由ACh产生的伊卡的减少可以单独解释环AMP水平的降低。
1. Ca currents (ICa) were measured by whole-cell patch clamp in single cells isolated from frog ventricle in which K currents were blocked with intracellular (120 mM) and extracellular (20 mM) Cs. Inward currents elicited by depolarizing voltage steps from a holding potential of -80 mV were blocked completely by 0.5 mM-Cd. 2. The quality of the voltage clamp was assessed using two patch electrodes on a single cell. One electrode was used in the voltage-clamp mode to measure membrane currents and the other in current-clamp to measure membrane potential. Ca currents as large as 2 nA were well clamped in cells as long as 210 .mu.m. 3. Acetylcholine (ACh) had no effect on ICa in the absence of .beta.-adrenergic stimulation but reduced to control levels ICa elevated by isoprenaline. Nanomolar concentrations of ACh were able to reduce significantly ICa elevated by 2 .mu.M-isoprenaline. 4. ACh had no effect on the shape of the I-V curve, on the reactivation (recovery from inactivation), or on the inactivation of ICa. Although isoprenaline increased ICa by an average of 6.5-fold, it had no effect on the shape of the I-V curve or on the inactivation at test potentials negative to +40 mV. However, isoprenaline slowed the half-reactivation time from a control value of 120 .+-. 10 ms (mean .+-. S.D.) to 153 .+-. 12 ms at -80 mV. 5. The effect of cyclic AMP on ICa was investigated using two patch electrodes, one filled with cyclic AMP. Maximal effects of cyclic AMP were observed with 5 .mu.M-cyclic AMP in the pipette. Maximal ICa was recorded several minutes after breaking the patch with the second electrode. After removing the cyclic-AMP-containing electrode, ICa declined to control levels after .apprx. 10 min. 6. 5 .mu.M-cyclic AMP in the patch electrode increased ICa by an average of 6.9-fold, but had no effect on the shape of the I-V curve or on inactivation. Cyclic AMP had a slowing effect on reactivation (half-reactivation time = 155 .+-. 24 ms) similar to that of isoprenaline. 7. ACh (1-10 .mu.M) did not reduce ICa elevated with cyclic AMP (0.1-20 .mu.M-cyclic AMP in the pipette). With low concentrations of cyclic AMP in the pipette (0.1 .mu.M), isoprenaline augmented ICa, but with 5 .mu.M-cyclic AMP in the pipette, isoprenaline was incapable of increasing ICa further. 8. These results suggest that the decrease of ICa produced by ACh can be explained solely by decreases in cyclic AMP levels.