Mechanisms involved in the regulation of mRNA for M₂ muscarinic acetylcholine receptors and endothelial and neuronal NO synthases in rat atria

Abstract

Background and purpose: Agonists of the M 2 muscarinic acetylcholine receptor (mAChR) increase mRNA for this receptor and mRNA for endothelial and neuronal isoforms of NO synthase (eNOS or nNOS). Here we examine the different signalling pathways involved in such events in rat cardiac atria. Experimental approach: In isolated atria, the effects of carbachol on mRNA for M 2 receptors, eNOS and nNOS were measured along with changes in phosphoinositide (PI) turnover, translocation of protein kinase C (PKC), NOS activity and atrial contractility. Key Results: Carbachol increased mRNA for M 2 receptors, activation of PI turnover, translocation of PKC and NOS activity and decreased atrial contractility. Inhibitors of phospholipase C (PLC), calcium/calmodulin (CaM), NOS and PKC prevented the carbachol-dependent increase in mRNA for M 2 receptors. These inhibitors also attenuated the carbachol induced increase in nNOS-and eNOS-mRNA levels. Inhibition of nNOS shifted the dose response curve of carbachol on contractility to the right, whereas inhibition of eNOS shifted it to the left. Conclusions and implications: From our results, activation of M 2 receptors induced nNOS and eNOS expression and activation of NOS up-regulated M 2 receptor gene expression. The signalling pathways involved included stimulation of PI turnover via PLC activation, CaM and PKC. nNOS and eNOS mediated opposing effects on the negative inotropic effect in atria, induced by stimulation of M 2 receptors. These results may contribute to a better understanding of the effects and side effects of cholinomimetic treatment in patients with cardiac neuromyopathy.

Epithelium integrity is crucial for the relaxant activity of brain natriuretic peptide in human isolated bronchi

“…Moreover, treatment with low concentrations of acetylcholine in epithelium‐denuded bronchi increased NO release. Intriguingly, NO‐mediated bronchorelaxation, secondary to M 2 muscarinic receptor activation, is more marked at lower than higher acetylcholine concentrations (Sterin‐Borda et al ., 1995; Range et al ., 1997; Ganzinelli et al ., 2007). In any case, in the present study, the maximal BNP‐dependent relaxant activity also increased in iNOS transcripts, confirming that NO synthesis plays a role in the downstream mechanisms of BNP‐dependent control of bronchial tone (Hamad et al ., 1997; Range et al ., 1997).…”

Exercise benefits cardiovascular health in hyperlipidemia rats correlating with changes of the cardiac vagus nerve

“…In addition, exercise increases eNOS expression in heart tissue (Grijalva et al 2008). Previous studies have indicated that nNOS and eNOS up-regulate M 2 receptor gene expression in rat hearts (Ganzinelli et al 2007), so this mechanism may contribute Fig. 6 Expression changes of M 2 receptors in the left ventricle of rats in the control (CON), aerobic training (AT), hyperlipidemia (HL), and hyperlipidemia plus aerobic training (HL + AT) groups.…”

“…The activation of the vagus nerve is therefore hypothesized to be reduced in the HL animals, given that the NO-cGMP pathway facilitates ACh release (Danson and Paterson 2003). In addition, endothelial nitric oxide synthase (eNOS) is veriWed to be decreased in hyperlipidemia, which down-regulates M 2 receptors expression (Ganzinelli et al 2007).…”

Molecular mechanisms of neuronal nitric oxide synthase in cardiac function and pathophysiology

“…nNOS gene regulation in tissues other than the myocardium. The genomic regulation (transcriptional and translational mechanisms) of cardiac nNOS is sparse, despite increased expression of nNOS mRNA and protein in LV or in atria following various pathophysiological insults (Takimoto et al 2002;Damy et al 2004;Danson et al 2004;Ganzinelli et al 2007). Understanding the transcriptional control of nNOS is important in defining the transcription/translation of specific nNOS splice variants in cardiovascular normal physiology and diseases.…”

“…; Ganzinelli et al . ). Understanding the transcriptional control of nNOS is important in defining the transcription/translation of specific nNOS splice variants in cardiovascular normal physiology and diseases.…”