Abstract 4141562: Functional evidence of regulation of the Na _V 1.5 channel through homomeric interaction of its α-subunits in the cellular membrane

Recent structural findings reveled potential interaction between Na V 1.5 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 V 1.5 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 V 1.5 surface density impacts R persist . Indeed, reduction of Na V 1.5 membrane density by paclitaxel (TXL, 100 µM, 2 hours) significantly increased R persist of multi- but not single-channel patches relative to untreated Na V 1.5 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 V 1.5 during fast inactivation, exhibited reduced inhibitory effect in multi- vs. single-channel patches. Confirming the dependence of R persist on Na V 1.5 membrane density, whole-cell patch clamp recordings in CHO cells transiently transfected with the inactivation-deficient ΔKPQ-Na V 1.5 mutant reveled a significant negative correlation between the magnitude of whole-cell peak I Na density and R persist . Notably, increasing Na V 1.5 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 V 1.5 homomeric interaction may impact Na V 1.5 kinetics and can serve as a therapeutic target for arrhythmia prevention.