Enhancement of closed-state inactivation in long QT syndrome sodium channel mutation DeltaKPQ.
DeltaKPQ, a three amino acid [lysine (K), proline (P), glutamine (Q)] deletion mutation of the human cardiac Na channel (hH1), which is one cause of long QT syndrome (LQT3), has impaired inactivation resulting in a late sodium current. To better understand inactivation in DeltaKPQ, we applied a site-3 toxin anthopleurin A, which has been shown to inhibit inactivation from the open state with little or no effect on inactivation from the closed state(s) in wild-type hH1. In contrast to the effect of site-3 toxins on wild-type hH1, inactivation from closed state(s) in toxin-modified DeltaKPQ demonstrated a large negative shift in the Na channel availability curve of nearly -14 mV. Recovery from inactivation showed that toxin-modified DeltaKPQ channels recovered slightly faster than those in control, whereas development of inactivation at potentials negative to -80 mV showed that inactivation developed much more rapidly in toxin-modified DeltaKPQ channels compared with control. An explanation for our results is that closed-state inactivation in toxin-modified DeltaKPQ is enhanced by the mutated inactivation lid being positioned "closer" to its receptor resulting in an increased rate of association between the inactivation lid and its receptor.
The Nora Eccles Harrison Cardiovascular Research and Training Institute, Salt Lake City, Utah 84112, USA.
Tiehua
T
Chen
Michael F
MF
Sheets
D002316:Cardiotonic Agents / Q000378:metabolism / Q000494:pharmacology; D002461:Cell Line, Transformed; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D007668:Kidney / Q000166:cytology; D008133:Long QT Syndrome / Q000503:physiopathology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009154:Mutation / Q000502:physiology; D018408:Patch-Clamp Techniques; D010455:Peptides / Q000378:metabolism / Q000494:pharmacology; D015222:Sodium Channels / Q000235:genetics* / Q000378:metabolism*
D002316:Cardiotonic Agents; D036341:Intercellular Signaling Peptides and Proteins; D010455:Peptides; D015222:Sodium Channels; C012746:anthopleurin-A