Tryptophan substitution of a putative D4S6 gating hinge alters slow inactivation in cardiac sodium channels.
Voltage-gated Na(+) channels display rapid activation gating (opening) as well as fast and slow inactivation gating (closing) during depolarization. We substituted residue S1759 (serine), a putative D4S6 gating hinge of human cardiac hNav1.5 Na(+) channels with A (alanine), D (aspartate), K (lysine), L (leucine), P (proline), and W (tryptophan). Significant shifts in gating parameters for activation and steady-state fast inactivation were observed in A-, D-, K-, and W-substituted mutant Na(+) channels. No gating shifts occurred in the L-substituted mutant, whereas the P-substituted mutant did not yield sufficient Na(+) currents. Wild-type, A-, D-, and L-substituted mutant Na(+) channels showed little or no slow inactivation with a 10-s conditioning pulse ranging from -180 to 0 mV. Unexpectedly, W- and K-substituted mutant Na(+) channels displayed profound maximal slow inactivation around -100 mV ( approximately 85% and approximately 70%, respectively). However, slow inactivation was progressively reversed in magnitude from -70 to 0 mV. This regression was minimized in inactivation-deficient hNav1.5-S1759W/L409C/A410W Na(+) channels, indicating that the intracellular fast-inactivation gate caused such a reversal. Our data suggest that the hNav1.5-S1759 residue plays a critical role in slow inactivation. Possible mechanisms for S1759 involvement in slow inactivation and for antagonism between fast and slow inactivation are discussed.
Wang
Sho-Ya
SY
Department of Biology, State University of New York, Albany, 12222, USA.
Russell
Corinna
C
Wang
Ging Kuo
GK
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D055592:Biophysical Phenomena; D001703:Biophysics; D002460:Cell Line; D006801:Humans; D066298:In Vitro Techniques; D015640:Ion Channel Gating; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009124:Muscle Proteins / Q000037:antagonists & inhibitors* / Q000737:chemistry* / Q000235:genetics; D016297:Mutagenesis, Site-Directed; D009206:Myocardium / Q000378:metabolism*; D062554:NAV1.5 Voltage-Gated Sodium Channel; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics; D015222:Sodium Channels / Q000737:chemistry* / Q000235:genetics; D014364:Tryptophan / Q000737:chemistry
D009124:Muscle Proteins; D062554:NAV1.5 Voltage-Gated Sodium Channel; D011994:Recombinant Proteins; C568320:SCN5A protein, human; D015222:Sodium Channels; D014364:Tryptophan