Cardiac Nav1.5 channels are modulated by epidermal growth factor receptor tyrosine kinase

Introduction: Nav1.5 is the pore-forming α-subunit protein of the cardiac sodium channels which plays a pivotal role in the initiation and propagation of the cardiac action potential. It is generally believed that cardiac sodium current (INa) is regulated by protein phosphorylation. Methods: The present study was designed to determine whether protein tyrosine kinases (PTKs) regulate human cardiac Nav1.5 channels stably expressed in HEK 293 cells using a whole-cell patch clamp technique. Results: It was found that human cardiac INa was enhanced by epidermal growth factor (EGF, 100 ng/mL) or the protein tyrosine phosphatases (PTPs) inhibitor orthovanadate (1 mM). The selective EGFR kinase inhibitor AG556 (5 µM) remarkably inhibited INa amplitude, shifted the inactivation voltage toward negative potentials, and slowed the recovery of INa from inactivation. These effects were antagonised by orthovanadate. However, insulin and the Src-family tyrosine kinase inhibitor PP2 had no significant effect on INa. Conclusion: These results suggest that EGFR kinase and PTPs regulate human cardiac Nav1.5 channels stably expressed in HEK-293 cells. EGFR kinase positively, while PTPs negatively modulates the channels. Additional experiments are required to confirm tyrosine phosphorylation level of Nav1.5 using immunoprecipitation and western blot analysis and to find out the tyrosine phosphorylation site(s) of Nav1.5 by site-directed mutagenesis