Remodeled connexin 43 hemichannels alter cardiac excitability and promote arrhythmias

Abstract

Connexin-43 (Cx43) is the most abundant protein forming gap junction channels (GJCs) in cardiac ventricles. In multiple cardiac pathologies, including hypertrophy and heart failure, Cx43 is found remodeled at the lateral side of the intercalated discs of ventricular cardiomyocytes. Remodeling of Cx43 has been long linked to spontaneous ventricular arrhythmia, yet the mechanisms by which arrhythmias develop are still debated. Using a model of dystrophic cardiomyopathy, we previously showed that remodeled Cx43 function as aberrant hemichannels (non-forming GJCs) that alter cardiomyocyte excitability and, consequently, promote arrhythmias. Here, we aim to evaluate if opening of remodeled Cx43 can serve as a general mechanism to alter cardiac excitability independent of cellular dysfunction associated with a particular cardiomyopathy. To address this issue, we used a genetically modified Cx43 knock-in mouse (S3A) that promotes cardiac remodeling of Cx43 protein without apparent cardiac dysfunction. Importantly, when S3A mice were subjected to cardiac stress using the β-adrenergic agonist isoproterenol (Iso), they displayed acute and severe arrhythmias, which were not observed in WT mice. Pretreatment of S3A mice with the Cx43 hemichannel blocker, Gap19, prevented Iso-induced abnormal electrocardiographic behavior. At the cellular level, when compared with WT, Iso-treated S3A cardiomyocytes showed increased membrane permeability, greater plasma membrane depolarization, and Ca2+ overload, which likely caused prolonged action potentials, delayed after depolarizations, and triggered activity. All these cellular dysfunctions were also prevented by Cx43 hemichannel blockers. Our results support the notion that opening of remodeled Cx43 hemichannels, regardless of the type of cardiomyopathy, is sufficient to mediate cardiac-stress-induced arrhythmogenicity.

Endothelial TRPV4/Cx43 Signaling Complex Regulates Vasomotor Tone in Resistance Arteries

“…TRPV4-activation induced a strongly ethidium uptake in ECs during the time (Figure 2D). Either inhibition of NO production with 100 µM L-NAME or the blockade of Cx43 hemichannels with 50 µM β-glycyrrhetinic acid (β-GA) or 50 µM Gap19-TAT, a specific Cx43 hemichannel blocker 15,16,24,25 , significantly reduced dye uptake increases. (Figure 2D).…”

“…In myoendothelial junctions, Snitrosylated Cx43 gap junction channels are crucial for regulating vascular diameter by facilitating the transmission of vital vasoactive molecules, such as Ca 2+ , IP 3 , NO, between endothelial and smooth muscle cells 12,13 . S-nitrosylation of Cx43 has been also shown to activate undocked hemichannels at the plasma membrane, influencing the membrane excitability of cardiomyocytes [14][15][16] . Specifically, they play pivotal roles in cardiac action potentials and the influx of Ca 2+ into cardiomyocytes under both normal conditions and during cardiac dysfunction 14,16,17 .…”

“…S-nitrosylation of Cx43 has been also shown to activate undocked hemichannels at the plasma membrane, influencing the membrane excitability of cardiomyocytes [14][15][16] . Specifically, they play pivotal roles in cardiac action potentials and the influx of Ca 2+ into cardiomyocytes under both normal conditions and during cardiac dysfunction 14,16,17 . Interestingly, the role of S-nitrosylated Cx43 hemichannels in normal vascular physiological processes like as in the EDH generation in ECs, as well as their role in regulating vasomotor tone, remains largely unexplored.…”

Connexins in Cancer, the Possible Role of Connexin46 as a Cancer Stem Cell-Determining Protein

“…It is important to note that Cx43-mediated arrhythmias are a complex phenomenon that extends beyond alterations in ion conduction via GJCs. It has been also demonstrated that Cx43 can form hemichannels that can open to the plasma membrane, allowing ion flux into the extracellular space and affecting cardiomyocyte excitability [76]. Consequently, Cx43 hemichannels have been proposed as potential targets for the arrhythmia treatment [74,77].…”

Structural basis of connexin-36 gap junction channel inhibition

“…Different GJCs also take an active role in cell growth and differentiation, tissue development and homeostasis 11 , and disruptions of connexin function can lead to severe pathological conditions. For example, dysfunctions in different connexin channels have been linked to deafness (Cx26) 12 , cataracts (Cx46 and Cx50) 13 , peripheral neuropathy (X-linked Charcot-Marie-Tooth disease, Cx32) 14 , cardiac arrhythmias (Cx40 and Cx43) 15,16 and various forms of cancer 17 .…”