Abstract Body (Do not enter title and authors here): Recent structural findings reveled potential interaction between Na_V1.5 in the plasma membrane. However, functional effects of this interaction on Na⁺ current (I_Na) remain elusive.
Cell-attached patch-clamp in Chinese hamster ovary (CHO) cells stably expressing Na_V1.5 revealed a significant increase in the ratio of persistent-to-peak I_Na (R_persist) in single- vs. multi-channel patches. These data suggest that reduced Na_V1.5 surface density impacts R_persist. Indeed, reduction of Na_V1.5 membrane density by paclitaxel (TXL, 100 µM, 2 hours) significantly increased R_persist of multi- but not single-channel patches relative to untreated Na_V1.5 expressing cells (Fig. 1). This was further supported by a divergence in peak I_Na predicted by a single-channel Markov model based on single-channel activity relative to experimental multi-channel recordings. To overcome the limitation of this classical model, we implemented a novel Markov model which accounts for channel interaction. Importantly, this approach not only replicated our experimental findings but also predicted a reduction of a fraction of channels in the fast inactivated state and consequently an acceleration of recovery from fast inactivation in multi-channel recordings (Fig. 2). Consistent with this prediction, experimental application of lidocaine (50 µM), an agent which blocks Na_V1.5 during fast inactivation, exhibited reduced inhibitory effect in multi- vs. single-channel patches. Confirming the dependence of R_persist on Na_V1.5 membrane density, whole-cell patch clamp recordings in CHO cells transiently transfected with the inactivation-deficient ΔKPQ-Na_V1.5 mutant reveled a significant negative correlation between the magnitude of whole-cell peak I_Na density and R_persist. Notably, increasing Na_V1.5 cluster density with SB216763 (5 µM) in cardiomyocytes isolated from mice harboring this mutation (ΔKPQ^+/-) significantly reduced whole-cell R_persist relative to untreated myocytes (Fig. 3).
Our study suggests that Na_V1.5 homomeric interaction may impact Na_V1.5 kinetics and can serve as a therapeutic target for arrhythmia prevention.