Molecular determinants of state-dependent block of voltage-gated sodium channels by pilsicainide.
OBJECTIVE
Pilsicainide, an anti-arrhythmic drug used in Japan, is described as a pure sodium channel blocker. We examined the mechanisms by which it is able to block open channels, because these properties may be especially useful to reduce hyperexcitability in pathologies characterized by abnormal sodium channel opening.


METHODS
The effects of pilsicainide on various heterologously expressed human sodium channel subtypes and mutants were investigated using the patch clamp technique.


RESULTS
Pilsicainide exhibited tonic and use-dependent effects comparable to those of mexiletine and flecainide on hNav1.4 channels. These use-dependent effects were abolished in the mutations F1586C and Y1593C within segment 6 of domain IV, suggesting that the interaction of pilsicainide with these residues is critical for its local anaesthetic action. Its affinity constants for closed channels (K(R)) and channels inactivated from the closed state (K(I)) were high, suggesting that its use-dependent block (UDB) requires the channel to be open for it to reach a high-affinity blocking site. Accordingly, basic pH, which slightly increased the proportion of neutral drug, dramatically decreased K(R) and K(I) values. Effects of pilsicainide were similar on skeletal muscle hNav1.4, brain hNav1.1 and heart hNav1.5 channels. The myotonic R1448C and G1306E hNav1.4 mutants were more and less sensitive to pilsicainide, respectively, due to mutation-induced gating modifications.


CONCLUSIONS
Although therapeutic concentrations of pilsicainide may have little effect on resting and closed-state inactivated channels, it induces a strong UDB due to channel opening, rendering the drug ideally suited for inhibition of high-frequency action potential firing.
Desaphy
J-F
JF
Department of Pharmacobiology, University of Bari, Bari, Italy. jfdesaphy@farmbiol.uniba.it
Dipalma
A
A
Costanza
T
T
Bruno
C
C
Lentini
G
G
Franchini
C
C
George
Al
A
Conte Camerino
D
D
D001921:Brain / Q000187:drug effects / Q000378:metabolism; D002460:Cell Line; D005424:Flecainide / Q000494:pharmacology; D006321:Heart / Q000187:drug effects; D006801:Humans; D008012:Lidocaine / Q000031:analogs & derivatives* / Q000494:pharmacology; D008801:Mexiletine / Q000494:pharmacology; D009124:Muscle Proteins / Q000187:drug effects / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism; D062550:NAV1.1 Voltage-Gated Sodium Channel; D062553:NAV1.4 Voltage-Gated Sodium Channel; D062554:NAV1.5 Voltage-Gated Sodium Channel; D009419:Nerve Tissue Proteins / Q000187:drug effects / Q000378:metabolism; D018408:Patch-Clamp Techniques; D026941:Sodium Channel Blockers / Q000494:pharmacology*; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism*
D009124:Muscle Proteins; D062550:NAV1.1 Voltage-Gated Sodium Channel; D062553:NAV1.4 Voltage-Gated Sodium Channel; D062554:NAV1.5 Voltage-Gated Sodium Channel; D009419:Nerve Tissue Proteins; C568242:SCN1A protein, human; C106251:SCN4A protein, human; C568320:SCN5A protein, human; D026941:Sodium Channel Blockers; D015222:Sodium Channels; D008801:Mexiletine; D008012:Lidocaine; C042288:pilsicainide; D005424:Flecainide