| First Author | Simon-Chica A | Year | 2021 |
| Journal | Cardiovasc Res | PubMed ID | 33823533 |
| Mgi Jnum | J:316006 | Mgi Id | MGI:6717223 |
| Doi | 10.1093/cvr/cvab126 | Citation | Simon-Chica A, et al. (2021) Novel insights into the electrophysiology of murine cardiac macrophages: relevance of voltage-gated potassium channels. Cardiovasc Res |
| abstractText | AIMS: Macrophages (MPhi), known for immunological roles such as phagocytosis and antigen presentation, have been found to electrotonically couple to cardiomyocytes (CM) of the atrio-ventricular node via Cx43, affecting cardiac conduction in isolated mouse hearts. Here, we characterise passive and active electrophysiological properties of murine cardiac resident MPhi, and model their potential electrophysiological relevance for CM. METHODS AND RESULTS: We combined classic electrophysiological approaches with 3 D florescence imaging, RNA-sequencing, pharmacological interventions and computer simulations. We used Cx3cr1eYFP/+ mice wherein cardiac MPhi were fluorescently labelled. FACS-purified fluorescent MPhi from mouse hearts were studied by whole-cell patch-clamp. MPhi electrophysiological properties include: membrane resistance 2.2 +/- 0.1 GOmega (all data mean+/-SEM), capacitance 18.3 +/- 0.1 pF, resting membrane potential -39.6 +/- 0.3 mV, and several voltage-activated, outward or inwardly-rectifying potassium currents. Using ion channel blockers (barium, TEA, 4-AP, margatoxin, XEN-D0103, DIDS), flow cytometry, immuno-staining and RNA-sequencing, we identified Kv1.3, Kv1.5 and Kir2.1 as channels contributing to observed ion currents. MPhi displayed four patterns for outward and two for inward-rectifier potassium currents. Additionally, MPhi showed surface expression of Cx43, a prerequisite for homo- and/or heterotypic electrotonic coupling. Experimental results fed into development of an original computational model to describe cardiac MPhi electrophysiology. Computer simulations to quantitatively assess plausible effects of MPhi on electrotonically coupled CM showed that MPhi can depolarise resting CM, shorten early and prolong late action potential duration, with effects depending on coupling strength and individual MPhi electrophysiological properties, in particular resting membrane potential and presence/absence of Kir2.1. CONCLUSIONS: Our results provide a first electrophysiological characterisation of cardiac resident MPhi, and a computational model to quantitatively explore their relevance in the heterocellular heart. Future work will be focussed at distinguishing electrophysiological effects of MPhi-CM coupling on both cell types during steady-state and in patho-physiological remodelling, when immune cells change their phenotype, proliferate, and/or invade from external sources. TRANSLATIONAL PERSPECTIVE: Cardiac tissue contains resident macrophages (MPhi) which, beyond immunological and housekeeping roles, have been found to electrotonically couple via connexins to cardiomyocytes (CM), stabilising atrio-ventricular conduction at high excitation rates. Here, we characterise structure and electrophysiological function of murine cardiac MPhi and provide a computational model to quantitatively probe the potential relevance of MPhi-CM coupling for cardiac electrophysiology. We find that MPhi are unlikely to have major electrophysiological effects in normal tissue, where they would hasten early and slow late CM-repolarisation. Further work will address potential arrhythmogenicity of MPhi in patho-physiologically remodelled tissue containing elevated MPhi-numbers, incl. non-resident recruited cells. |
