不同信号分子参与M胆碱能受体激动剂对不同胚胎发育阶段小鼠心肌细胞起搏电流的调控

应用全细胞膜片钳技术,研究了M胆碱能对不同孕期的胚胎小鼠心肌细胞的起搏电流(If)的调节。我们发现,在胚胎发育的早期阶段,M胆碱能受体激动剂(muscarinic agonist carbachol,CCh)明显抑制If,但在胚胎发育的晚期阶段,CCh对If的抑制作用消失。腺苷酸环化酶(adeinylate cyclase,AC)激动剂毛喉素Forskolin和非选择性磷酸二酯酶(PDE)抑制剂IBMX均可增强发育早期阶段和晚期阶段的If。但有趣的是,尽管,Forskolin和IBMX可增加基础If,它们对CCh抑制的If的作用却大不相同。在胚胎发育的早期阶段,Forskolin不能拮抗CCh对If的抑制作用,但IBMX可以。在发育的中期阶段Forskolin可以拮抗CCh的抑制作用,但IBMX不可以。因此,我们推断,CCh可能是通过调控细胞内的CAMP水平来调节If的。但是在胚胎发育的早期阶段和中期阶段,CCh可能通过不同的信号转导通路来实现对胞内cAMP的水平调控。在发育的早期阶段,CCh主要是通过增强PDE的活性,加速cAMP的降解而实现对f的调控。而在发育的中期阶段,CCh则主要通过与AC耦联,抑制其活性,通过减慢cAMP的合成而实现对If的调控。

Different signal molecules involved in the muscarinic modulation of pacemaker current I(f) on the heart of mouse embryo in different developmental stages

We isolated mouse embryonic cardiomyocytes derived from timed-pregnant females at different periods and used patch-clamp technique to investigate the muscarinic cholinergic modulation of pacemaker current If in different developmental stages. In early development stage (EDS), muscarinic agonist carbachol (CCh) significantly decreased the magnitude of the pacemaker current If but had no effect in late development stage (LDS). Forskolin (a direct adenylate cyclase activator) and IBMX (a non-selective phosphodi-esterase inhibitor) increased If in both EDS and LDS cells. Interestingly, although both forskolin and IBMX increased basal If, their effects on CCh-inhibited If were different. Forskolin did not reverse the inhibitory action of CCh until intermediate development stage (IDS). In contrast, IBMX reversed the inhibitory action of CCh on If in EDS but not in IDS. It is suggested that a decrease in intracellular cAMP is a possible mechanism for CCh to modulate If. During the EDS and IDS CCh controls the cytoplasmic cAMP level by different pathways: In EDS, CCh modulates If possibly by activating PDE which accelerates the breakdown of cAMP, but in IDS possibly by inhibiting adenylate cyclase (AC) which then reduces the synthesis of cAMP.