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

摘要

Suppression of cardiac voltage-gated Na~+ currents is probably one of the important factors for the cardioprotective effects of the n-3 polyunsaturated fatty acids (PUFAs) against lethal arrhythmias. The α subunit of the human cardiac Na~+ channel (hH1_α) and its mutants were expressed in human embryonic kidney (HEK293t) cells. The effects of single amino acid point mutations on fat'ty acid-induced inhibition of the hH1_α Na~+ current (I_Na) were as- sessed. Eicosapentaenoic acid (EPA, C20:5n-3) significantly reduced I_Na in HEK293t cells expressing the wild type, Y1767K, and F1760K of hH1_α Na~+ channels. The inhibition was voltage and concentra- tion-dependent with a significant hyperpolarizing shift of the steady state of I_Na. In contrast, the mutant N406K was significantly less sensitive to the inhibitory effect of EPA. The values of the shift at 1, 5, and 10 μM EPA were significantly smaller for N406K than for the wild type. Coexpression of the β1 subunit and N406K further decreased the inhibitory effects of EPA on I_Na in HEK293t cells. In addition. EPA produced a smaller hyperpolarizing shift of the V_1/2 of the steady-state inactivation in HEK293t cells coexpress- ing the β1 subunit and N406K. These results demonstrate that substitution of asparagine with lysine at the site of 406 in the domain-1-segment-6 region (D1-S6) significantly decreased the inhibitory effect of PUFAs on I_Na., and coexpression with β1 de- creased this effect even more. Therefore. asparagine at the 406 site in hH1_α may be important for the inhibition by the PUFAs of cardiac voltage-gated Na~+ currents. which play a significant role in the antiarrhythmic actions of PUFAs.