The endogenous cardiac cholinergic system: a robust and independent regulator of ventricular conduction

This commentary refers to ‘An endogenous cholinergic system controls electrical conduction in the heart’, by D. Xie et al, https://doi.org/10.1093/eurheartj/ehae699 and ‘Another pathophysiological feature of the impairment of the non-neuronal cardiac cholinergic system that leads to arrhythmogenesis’, by Y. Kakinuma, https://doi.org/10.1093/eurheartj/ehaf1108. We thank Dr. Yoshihiko Kakinuma for his thoughtful commentary on our recent work.1 His expertise in the non-neuronal cardiac cholinergic system (NNCCS) is well recognized, and we appreciate this opportunity to address his three main points. Regarding the use of 100 µM acetylcholine (ACh) in our patch-clamp studies, the local ACh concentration in the cardiomyocyte microenvironment remains unknown. In non-neuronal cholinergic systems, ACh can accumulate in confined intercellular spaces, reaching concentrations far exceeding typical synaptic levels.2 Higher ACh concentrations are often methodologically necessary in patch-clamp studies of non-neuronal tissues to elicit reproducible currents owing to diffuse, non-synaptic transmitter release.3–5 Our dose-response experiments showed a clear concentration-dependent effect, and the consistent use of 100 µM ACh across antagonist tests ensured internal validity. The abolition of currents by mecamylamine and α-bungarotoxin, but not atropine, strongly supports the specificity of nicotinic ACh receptors (nAChRs) in this response.