Block of inactivation-deficient cardiac Na(+) channels by acetyl-KIFMK-amide.
The Na(+) channel alpha-subunit contains an IFM motif that is critical for the fast inactivation process. In this study, we sought to determine whether an IFM-containing peptide, acetyl-KIFMK-amide, blocks open cardiac Na(+) channels via the inner cavity. Intracellular acetyl-KIFMK-amide at 2mM elicited a rapid time-dependent block (tau=0.24 ms) of inactivation-deficient human heart Na(+) channels (hNav1.5-L409C/A410W) at +50 mV. In addition, a peptide-induced tail current appeared conspicuously upon repolarization, suggesting that the activation gate cannot close until acetyl-KIFMK-amide is cleared from the open pore. Repetitive pulses (+50 mV for 20 ms at 1Hz) produced a substantial use-dependent block of both peak and tail currents by approximately 65%. A F1760K mutation (hNav1.5-L409C/A410W/F1760K) abolished the use-dependent block by acetyl-KIFMK-amide and hindered the time-dependent block. Competition experiments showed that acetyl-KIFMK-amide antagonized bupivacaine binding. These results are consistent with a model that two acetyl-KIFMK-amide receptors exist in proximity within the Na(+) channel inner cavity.
Wang
Sho-Ya
SY
Department of Biology, State University of New York at Albany, Albany, NY, USA. wang@zeus.bwh.harvard.edu
Wang
Ging Kuo
GK
D019943:Amino Acid Substitution; D002478:Cells, Cultured; D015640:Ion Channel Gating / Q000187:drug effects* / Q000502:physiology*; D007668:Kidney / Q000378:metabolism / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects* / Q000502:physiology*; D009124:Muscle Proteins / Q000187:drug effects* / Q000502:physiology*; D016297:Mutagenesis, Site-Directed; D062554:NAV1.5 Voltage-Gated Sodium Channel; D009842:Oligopeptides / Q000494:pharmacology*; D011994:Recombinant Proteins / Q000378:metabolism; D026941:Sodium Channel Blockers / Q000494:pharmacology*; D015222:Sodium Channels / Q000187:drug effects* / Q000502:physiology*; D013329:Structure-Activity Relationship
D009124:Muscle Proteins; D062554:NAV1.5 Voltage-Gated Sodium Channel; D009842:Oligopeptides; D011994:Recombinant Proteins; C568320:SCN5A protein, human; D026941:Sodium Channel Blockers; D015222:Sodium Channels; C500155:acetyl-lysyl-leucyl-phenylalanyl-methionyl-lysinamide