Abstract 13235: Enhanced Receptor-independent Nucleoside Diphosphate Kinase Mediated Gs Protein Signaling Contributes to Arrhythmogenic Calcium Mishandling in Atrial Fibrillation
Background: Enhanced G-protein related cyclic AMP (cAMP) signaling and abnormal Ca2+ handling due to dysfunctional ryanodine receptor type-2 (RyR2) are implicated in atrial fibrillation (AF). Nucleoside diphosphate kinase (NDPK) forms complexes with Gs proteins, increasing cAMP signaling via receptor-independent G protein activation. Here, we studied the possible proarrhythmic role of NDPKs in clinical (chronic AF, cAF) and experimental AF.
Methods: NDPK and G protein expression were assessed by immunoblotting in atria from sinus rhythm (Ctl) and cAF patients; dogs undergoing AF-mimicking tachycardia remodeling (ATR, 400 bpm, 7 days) or AF-promoting chronic atrial ischemia; and canine atrial cardiomyocytes (CMs) paced in vitro for 24-48 hrs at 1 (P1) or 3 Hz (P3). cAMP was measured by immunoassay. Immunostaining was used for protein visualization. Spontaneous sarcoplasmic reticulum (SR) Ca2+ release events (SCaEs) in CMs overexpressing NDPKs or EGFP-control (adenoviral gene-transfer) were recorded with epifluorescence (Indo-1).
Results: NDPK-B, NDPK-C, Gαs and Gβ1 were upregulated in cAF patient atria (Fig A). ATR and chronic atrial ischemia increased NDPK-B expression in canine atria (Fig B). In vitro tachypacing reproduced AF effects on NDPK/Gαs in CMs (Fig C). Accordingly, cAMP levels were higher in cAF patients and P3-paced CMs (Fig D-E). Adenoviral NDPK-B and NDPK-C overexpression increased cAMP levels (Fig F). NDPK-B, NDPK-C and Gαs co-localized at the plasma membrane when upregulated by tachypacing canine CMs. SCaEs, a proarrhythmic consequence of diastolic SR Ca2+ leak, were enhanced in NDPK-B or NDPK-C overexpressing CMs, and the latency from last regular SR Ca2+ release was reduced (Fig G).
Conclusions: Receptor-independent NDPK-mediated Gs-protein/cAMP signaling is upregulated in clinical and experimental AF, causes arrhythmogenic SCaEs, and is likely a novel contributor to ectopy-inducing atrial triggered activity due to SR Ca2+ leak.
Author Disclosures: M. Schaefer: None. I. Abu-Taha: None. P. Naud: None. X. Qi: None. V. Gundlach: None. M. Kamler: None. T. Wieland: None. S. Nattel: None. D. Dobrev: Consultant/Advisory Board; Modest; OMEICOS Therapeutics GmbH, Berlin: consultancy fees, research grant, XENTION Limited, Cambridge: consultancy fees, research grant.
- © 2016 by American Heart Association, Inc.