氨甲酰胆碱增加大鼠心室肌细胞收缩机制的初步研究

PRELIMIARY STUDIES OF THE MECHANISM OF CARBACHOL INCREASE CONTRACTION IN RAT VENTRICULAR MYOCYTES

目的 :本文研究非选择性M受体激动剂氨甲酰胆碱 (Cch)对心肌细胞收缩的作用 ,并同时观察L—型钙流 ,探讨其机制。方法 :以分离大鼠的单个心室肌细胞为对象 ,采用膜片钳和单细胞收缩测量技术 ,在 35℃恒温 ,细胞外钙离子浓度 1.8mmol/L ,0 .2Hz,1.0Hz刺激下测量细胞收缩幅度和ICa(L) 、INa/Ca。结果 :①大鼠心肌细胞收缩与刺激频率呈负相关 ;②选择△L0 .2Hz/△L1.0Hz≥ 1.2 5 (n =6 )的细胞给予 1.0Hz的刺激 ,10 0 μmol/LCch增加大鼠心室肌细胞收缩 2 8%。③Cch作用能被非选择性M受体阻滞剂阿托品阻滞 ,选择性M1受体激动剂MCN A 34310 0 μmol/L对细胞收缩无影响。④ 10 0 μmol/LCch对ICa(L) 无影响 ,但增加从 +10mV复极到 - 4 0mV所产生的晚期尾电流 ,提示INa/Ca加大。结论 :Cch能加强大鼠心室肌细胞收缩 ,它的作用由M2 受体介导 ,其机制可能是通过加强INa/Ca,增加肌质网 (SR)内的钙内容和钙释放 ,导致细胞收缩加强 。

Aim: To study whether the mAchR agonist Carbachol(Cch, nonselective) causes increased contractions and L-type Ca^(2+) current in ventricular myocytes and the mechanism of these effects. Methods: The effect of Cch on the I_(Ca(L)) and Na/Ca exchange current(I_(Na/Ca)) was studied in patch-clamped ventricular myocytes isolated from rat hearts and superfused with Tyrode's solution (35℃,1.8mmol/L _o) and stimulated at 0.2 Hz and 1.0 Hz evoke contractions of single myocyte. Results: ① An increase of stimulation frequency decreased the contractions of myocytes(negative inotropic effects).② 100 μmol/L Cch increased contraction in 6 cells by 28% (△L_(0.2 Hz)/△L_(1.0 Hz)≥1.25) at 1.0 Hz stimulus frequency.③ The mAchR antagonist Atropine prevented the Cch effect. The mAchR agonist McN-A-343(M_1-selective) did not change the contractions in most of the cells.④ 100 μmol/L Cch had no significant effect on basal I_(Ca(L)), but increased the tail current density on repolarization from +10 mV to -40 mV, suggested that Cch increased I_(Na/Ca).Conclusion: The increase of cell contractions by Cch is apparently mediated by M_2 mAchR and eventually increased I_(Na/Ca). The increase Ca^(2+) content of the SR is reflected by the greater magnitude of I_(Na/Ca). These results provide an explanation for the increased contraction of the rat ventricular myocytes by Cch and without changes in I_(Ca(L)).