Abstract 17193: Inhibiting Late Sodium Current Attenuates Isoproterenol-Induced Transient Inward Current and Delayed Afterdepolarizations in Ventricular Myocytes
Introduction: The β-adrenergic agonist isoproterenol (ISO) is known to induce the arrhythmogenic transient inward current (ITi) and delayed afterdepolarization (DAD) via a stimulation of L-type Ca2+ current. Recent studies found that ISO-induced DADs in cardiac tissues are inhibited by GS967, a selective blocker of the late Na+ current (INaL). Thus, we hypothesize that INaL contributes to the actions of ISO, and selective inhibition of this current will reduce ISO-induced ITi and DADs.
Methods: Transmembrane currents and action potentials of rabbit and guinea pig (GP) ventricular myocytes were recorded using the whole-cell patch-clamp technique. ISO (0.1 μM), GS967 (1 μM) and the Na+ channel blocker tetrodotoxin (TTX, 3 μM) were used in the experiments.
Results: In rabbit myocytes, application of ISO caused an increase in the amplitude of INaL from -0.10±0.03 to -0.32±0.04 pA/pF (n = 17, p < 0.05). The ISO-stimulated INaL was inhibited by GS967 and TTX. In one series of experiments, ISO increased the INaL from -0.14±0.04 to -0.35±0.06 pA/pF, and GS967 applied in the presence of ISO reduced the current to -0.14±0.03 pA/pF (n = 9, p < 0.05). In another series of experiments, the amplitude of INaL was increased by ISO from -0.17±0.08 to -0.41±0.09 pA/pF, and was decreased to -0.09±0.08 pA/pF when TTX was applied with ISO (n = 5, p < 0.05). Application of ISO also induced ITi and DADs. GS967 applied in the presence of ISO inhibited the amplitude of ITi by 52±6%, from -1.79±0.30 to -0.87±0.16 pA/pF (n = 8, p < 0.05). Consistent with the inhibition of ITi, GS967 suppressed the amplitude of ISO-induced DADs by 56±12%, from 6.54±1.59 to 3.22±1.27 mV (n = 5, p < 0.05). Similarly, in GP myocytes ISO-induced ITi and DADs were decreased by GS967 from -1.14±0.21 to -0.73±0.16 pA/pF (n = 7, p < 0.05) and from 7.16±0.59 to 4.67±0.24 mV (n = 5, p < 0.05), respectively.
Conclusions: An increased INaL is likely to contribute to the proarrhythmic effects of ISO in cardiac myocytes. GS967 significantly attenuated ISO-induced INaL, ITi and DADs, suggesting that inhibiting this current could be an effective strategy to antagonize the arrhythmogenic actions of β-adrenergic stimulation.
Author Disclosures: Y. Song: Research Grant; Significant; Gilead Sciences. N. El-Bizri: Employment; Significant; Gilead Sciences. S. Rajamani: Employment; Significant; Gilead Sciences. L. Belardinelli: Employment; Significant; Gilead Sciences.
- © 2015 by American Heart Association, Inc.