Impaired Intracellular Calcium Buffering Contributes to the Arrhythmogenic Substrate in Atrial Myocytes From Patients With Atrial Fibrillation


Fakuade FE, Hubricht D, Möller V, Sobitov I, Liutkute A, Döring Y, Seibertz F, Gerloff M, Pronto JRD, Haghighi F, Brandenburg S, Alhussini K, Ignatyeva N, Bonhoff Y, Kestel S, El-Essawi A, Jebran AF, Großmann M, Danner BC, Baraki H, Schmidt C, Sossalla S, Kutschka I, Bening C, Maack C, Linke WA, Heijman J, Lehnart SE, Kensah G, Ebert A, Mason FE, Voigt N




Circulation. 2024 Jun 24.


BACKGROUND: Alterations in the buffering of intracellular Ca2+, for which myofilament proteins play a key role, have been shown to promote cardiac arrhythmia. It is interesting that although studies report atrial myofibrillar degradation in patients with persistent atrial fibrillation (persAF), the intracellular Ca2+ buffering profile in persAF remains obscure. Therefore, we aim to investigate the intracellular buffering of calcium and its potential arrhythmogenic role in persAF.
METHODS: Simultaneous transmembrane fluxes (patch-clamp) and intracellular Ca2+ signaling (fluo-3-acetoxymethyl ester) were recorded in myocytes from right atrial biopsies of sinus rhythm (control) and patients with persAF, alongside human atrial subtype induced pluripotent stem cell–derived cardiac myocytes (iPSC-CMs). Protein levels were quantified by immunoblotting of human atrial tissue and induced pluripotent stem cell–derived cardiac myocytes. Mouse whole heart and atrial electrophysiology was measured on a Langendorff system.
RESULTS: Cytosolic Ca2+ buffering was decreased in atrial myocytes of patients with persAF because of a depleted amount of Ca2+ buffers. In agreement, protein levels of selected Ca2+ binding myofilament proteins, including cTnC (cardiac troponin C), a major cytosolic Ca2+ buffer, were significantly lower in patients with persAF. Small interfering RNA (siRNA)–mediated knockdown of cTnC in induced pluripotent stem cell–derived cardiac myocytes (si-cTnC) phenocopied the reduced cytosolic Ca2+ buffering observed in persAF. Si-cTnC induced pluripotent stem cell–derived cardiac myocytes exhibited a higher predisposition to spontaneous Ca2+ release events and developed action potential alternans at low stimulation frequencies. Last, indirect reduction of cytosolic Ca2+ buffering using blebbistatin in an ex vivo mouse whole heart model increased vulnerability to tachypacing-induced atrial arrhythmia, validating the direct mechanistic link between impaired cytosolic Ca2+ buffering and atrial arrhythmogenesis.
CONCLUSIONS: Our findings suggest that loss of myofilament proteins, particularly reduced cTnC protein levels, causes diminished cytosolic Ca2+ buffering in persAF, thereby potentiating the occurrence of spontaneous Ca2+ release events and AF susceptibility. Strategies targeting intracellular buffering may represent a promising therapeutic lead in AF management.


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