L-cysteine prevents oxidation-induced block of the cardiac Na+ channel via interaction with heart-specific cysteinyl residues in the P-loop region.
The present study investigated the protective effects of L-cysteine on the oxidation-induced blockade of Na+ channel a-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 3,000 micromol/L. Hg2+, a potent sulfhydryl oxidizing agent, blocked hH1 with a time to 50% inhibition (Time50%) of 20s. Preperfusion of COS7 cells with 100 micromol/L L-cysteine significantly slowed the Hg2+ block of hH1 (Time50% = 179 s). L-cysteine did not prevent Hg2+ block of hSkM1 (Time50% = 37s) or the C373Y hH1 mutant (Time50% = 43s). As for other sulfo-amino acids, homocysteine prevented the Hg2+ block of hH1, with the Time50% (70s) being significantly smaller than that of L-cysteine, whereas methionine did not prevent the Hg2+ block of hH1. L-cysteine did not prevent the Cd2+ block of hH1. These results indicate that L-cysteine selectively acts on heart-specific Cys373 in the P-loop region of hH1 to prevent Cys373 from the oxidation-induced sulfur-Hg-sulfur bridge formation.
Yatsuhashi
Toru
T
Department of Medicine, Faculty of Medicine, Tottori University, Yonago, Japan.
Hisatome
Ichiro
I
Kurata
Yasutaka
Y
Sasaki
Norihito
N
Ogura
Kazuyoshi
K
Kato
Masaru
M
Kinugasa
Ryoji
R
Matsubara
Koichi
K
Yamawaki
Masahiro
M
Yamamoto
Yasutaka
Y
Tanaka
Yasunori
Y
Ogino
Kazuhide
K
Igawa
Osamu
O
Makita
Naomasa
N
Shigemasa
Chiaki
C
D003545:Cysteine / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D006710:Homocysteine / Q000494:pharmacology; D006801:Humans; D008628:Mercury / Q000494:pharmacology; D008715:Methionine / Q000494:pharmacology; D009206:Myocardium / Q000166:cytology; D010084:Oxidation-Reduction; D018408:Patch-Clamp Techniques; D015222:Sodium Channels / Q000187:drug effects* / Q000235:genetics
D015222:Sodium Channels; D006710:Homocysteine; D008715:Methionine; D008628:Mercury; D003545:Cysteine