L-cysteine prevents oxidation-induced block of the cardiac Na + channel via interaction with heart-specific cysteinyl residues in the P-loop region

Abstract

The present study investigated the protective effects of L-cysteine on the oxidation-induced blockade of Na + channel α-subunits, hH1 (cardiac) and hSkM1 (skeletal), expressed in COS7 cells. Na + currents were recorded by the whole-cell patch clamp technique (n=3-7). L-cysteine alone blocked hH1 and hSkM1 in a dose-dependent manner, with saturating L-cysteine block at 3,000μmol/L. Hg 2+, a potent sulfhydryl oxidizing agent, blocked hH1 with a time to 50% inhibition (Time50%) of 20s. Preperfusion of COS7 cells with 100μmol/L Lcysteine significantly slowed the Hg 2+ block of hH1 (Time50% = 179s). L-cysteine did not prevent Hg 2+ block of hSkM1 (Time50%=37s) or the C373Y hH1 mutant (Time50%=43s). As for other sulfo-amino acids, homocysteine prevented the Hg 2+ block of hH1, with the Time50% (70s) being significantly smaller than that of L-cysteine, whereas methionine did not prevent the Hg 2+ block of hH1. L-cysteine did not prevent the Cd 2+ block of hH1. These results indicate that L-cysteine selectively acts on heart-specific Cys 373 in the P-loop region of hH1 to prevent Cys 373 from the oxidation-induced sulfur-Hg-sulfur bridge formation.