Shen J B, Jiang B, Pappano A J
Department of Pharmacology, University of Connecticut Health Center, Farmington, Connecticut, USA.
J Pharmacol Exp Ther. 1999 Aug;290(2):641-8.
We asked whether agonist occupancy of M(1) muscarinic receptor (mAChR) causes increased L-type Ca(2+) [I(Ca(L))] and contractions in ventricular myocytes. Voltage-clamp pulses evoked I(Ca(L)) in guinea pig ventricular myocytes superfused with Tyrode's solution (22-24 degrees C). The mAChR agonists carbachol (Cch, nonselective), McN-A-343 (McN, M(1)-selective), and oxotremorine (Oxo, M(2)-selective) were tested at 0.1 mM. None of these agonists affected basal I(Ca(L)). McN did not change isoproterenol-stimulated I(Ca(L)) in 13 of 15 cells. The slight decrease in two cells was not muscarinic because atropine (1 microM) did not antagonize it. Carbachol or Oxo decreased isoproterenol-stimulated I(Ca(L)) by 87 +/- 6.7 (n = 8 cells) and 49 +/- 9.0% (n = 4 cells), respectively. Atropine blocked inhibition by Cch or Oxo. External stimulation evoked contractions of single myocytes (35 degrees C). McN increased contraction in 1 of 22 cells stimulated at 0.2 Hz and in 0 of 16 cells stimulated at 1.0 Hz. Carbachol significantly increased contraction in 10 of 15 cells at 0.2 Hz and in 8 of 10 cells at 1.0 Hz stimulus frequency. Summarily, the M(1)-selective agonist McN had a negligible role to regulate I(Ca(L)). The antiadrenergic effect of mAChR agonists is attributable to M(2) receptor occupancy. That Cch, but not McN, increased cell shortening excludes participation of M(1) mAChR in the stimulant effect of Cch on guinea pig ventricular myocyte contractions.
我们研究了毒蕈碱M(1)受体（mAChR）激动剂占据受体是否会导致心室肌细胞中L型钙电流[I(Ca(L))]增加和收缩增强。在22 - 24℃用台氏液灌流的豚鼠心室肌细胞中，通过电压钳脉冲诱发I(Ca(L))。分别以0.1 mM的浓度测试了mAChR激动剂卡巴胆碱（Cch，非选择性）、 McN - A - 343（McN，M(1)选择性）和氧化震颤素（Oxo，M(2)选择性）。这些激动剂均未影响基础I(Ca(L))。在15个细胞中的13个细胞中，McN未改变异丙肾上腺素刺激的I(Ca(L))。在另外两个细胞中出现的轻微下降并非由毒蕈碱作用引起，因为阿托品（1 microM）不能拮抗这种下降。卡巴胆碱或氧化震颤素分别使异丙肾上腺素刺激的I(Ca(L))降低了87±6.7%（n = 8个细胞）和49±9.0%（n = 4个细胞）。阿托品可阻断Cch或氧化震颤素的抑制作用。外部刺激诱发单个肌细胞收缩（35℃）。在0.2 Hz刺激时，22个细胞中有1个细胞的收缩增强，在1.0 Hz刺激时，16个细胞中无细胞收缩增强。在0.2 Hz刺激频率下，15个细胞中有10个细胞的收缩显著增强，在1.0 Hz刺激频率下，10个细胞中有8个细胞的收缩显著增强。总之，M(1)选择性激动剂McN对调节I(Ca(L))的作用可忽略不计。mAChR激动剂的抗肾上腺素能作用归因于M(2)受体的占据。卡巴胆碱而非McN增加细胞缩短，这排除了M(1) mAChR参与卡巴胆碱对豚鼠心室肌细胞收缩的刺激作用。
