Single point mutations affect fatty acid block of human myocardial sodium channel a subunit Na+ channels

Suppression of cardiac voltage-gated Naf currents is probably one of the im portant factors for the cardioprotective effects of the n-3 polyunsaturated fatty acids (PUFAs) against lethal arrhythmias. The a subunit of the human cardiac Na+ channel (hH1(alpha)) and its mutants were expressed in human e mbryonic kidney (HEK293t) cells. The effects of single amino acid point mut ations on fatty acid-induced inhibition of the hH1(alpha) Na+ current (I-Na ) were assessed. Eicosapentaenoic acid (EPA, C20:5n-3) significantly reduce d INa in HEK293t cells expressing the wild type, Y1767K, and F1760K of hH1( alpha) Na+ channels. The inhibition was voltage and concentration-dependent with a significant hyperpolarizing shift of the steady state of IN,. In co ntrast, the mutant N406K was significantly less sensitive to the inhibitory effect of EPA. The values of the shift at 1, 5, and 10 muM EPA were signif icantly smaller for N406K than for the wild type. Coexpression of the beta (1) subunit and N406K further decreased the inhibitory effects of EPA on IN , in HEK293t cells. In addition, EPA produced a smaller hyperpolarizing shi ft of the V-1/2 of the steady-state inactivation in HEK293t cells coexpress ing the pr subunit and N406K. These results demonstrate that substitution o f asparagine with lysine at the site of 406 in the domain-1-segment-6 regio n (D1-56) significantly decreased the inhibitory effect of PUFAs on I-Na, a nd coexpression with beta (1) decreased this effect even more. Therefore, a sparagine at the 406 site in hH1(alpha) may be important for the inhibition by the PUFAs of cardiac voltage-gated Na+ currents, which play a significa nt role in the antiarrhythmic actions of PUFAs.