Late sodium current in synergism with Ca ²⁺ /calmodulin-dependent protein kinase II contributes to β-adrenergic activation-induced atrial fibrillation

Figures

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  Figure 1.. Representative records of AF in the absence (control) and presence of isoproterenol (ISO; 15nM) treated with either ranolazine (RAN), eleclazine (ELEC), or KN-93 in rabbit-isolated hearts. Hearts were paced at 4.5 Hz in right atrium. MAP (upper recordings in each panel) and an ECG (lower recordings in each panel) were recorded simultaneously. The MAP and ECG traces under programmed stimulation of hearts treated with either vehicle or drugs as shown on the top of each panel.

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  Figure 2.. Concentration–response relationships of drugs on AF incidence (a), inducible window (b) and burden (c) induced by isoproterenol (ISO) in the absence (n = 12) and presence of sea anemone toxin II (ATX-II; 2 nM, n = 6) and treated with either ranolazine (RAN; n = 8), eleclazine (ELEC; n = 8), KN-93 (n = 8), or KN-92 (n = 6) in rabbit-isolated hearts. (i) Concentration–response relationships of ISO on AF in the absence and presence of ATX-II (2 nM); (ii) concentration–response relationships of RAN, ELEC, KN −93 or KN-92 on AF induced by ISO (15 nM). 0, ISO alone; *p < 0.05 versus control (CTL); **p < 0.05 versus ISO alone.

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  Figure 3.. Effects of drugs on inhomogeneity of atrial conduction. (a) The index of inhomogeneity (IHI) at a fixed rate (baseline) and at the first beat of AF in hearts treated with either isoproterenol (ISO; 15 nM) alone or ISO + ranolazine (RAN; 10 µM, n = 6), ISO + eleclazine (ELEC; 10 µM, n = 6) or ISO + KN-93 (3 µM, n = 6). (b) Representative examples of epicardial conduction properties of left atrium by multi-electrode array in the absence (i) and presence (ii) of ISO at baseline, and treated with ISO (iii) and ISO + ELEC (10 µM) (iv) at the first beat of AF. *p < 0.05 versus control (CTL); **p < 0.05 versus ISO at baseline; ***p < 0.05 versus ISO + drugs at the first beat of AF.

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  Figure 4.. Reverse effects of late INa or CaMKII inhibitors on phosphorylation of Nav1.5 and CaMKII (a) and late INa (b) treated with vehicle (CTL), isoproterenol (ISO; 15 nM) or ISO + ranolazine (RAN), eleclazine (ELEC) and KN-93 (3 µM) respectively. (a) Representative Western blots (i) and the relative levels (ii) phospho-NaV1.5 (P-Nav1.5; n = 5) and phospho-CaMKII (P-CaMKII-δ; n = 5, normalized to GAPDH and expressed relative to normal levels) protein expression are presented. (b) Representative records (i, n = 5) and summarized absolute values (ii, n = 5) of late INa are presented. *p < 0.05 versus control (CTL); **p < 0.05 versus ISO alone.

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  Figure 5.. Late INa and CaMKII inhibitors reduced early/delay afterdepolarizations (EADs/DADs) in atrial myocytes induced by isoproterenol (ISO; 15 nM). Original records of action potential ((a): EAD (a), DAD (b), n = 10) and summarized data ((b), n = 5) are presented. *p < 0.05 versus control (CTL); **p < 0.05 versus ISO alone.

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  Figure 6.. The combined used of late INa and CaMKII inhibitors had synergistic inhibitive effects on isoproterenol (ISO)-induced AF. Combined use of KN-93 (0.03 µM) with either ranolazine (RAN; 0.1 µM) or eleclazine (ELEC; 0.3 µM) were superior to that when each drug was used alone or the sum of the effects of two drugs (either KN-93 and RAN or KN-93 and ELEC, n = 5) in reducing the incidence, inducible window and burden of AF in the continued presence of ISO. *p < 0.05 versus individual effects or the sum (not shown) of the effects of two agents when they were used individually.