Actions of ATX-II and other gating-modifiers on Na(+) currents in HEK-293 cells expressing WT and DeltaKPQ hNa(V) 1.5 Na(+) channels.
Voltage-gated Na(+) channels underlie the action potential upstroke in excitable cells, and both natural and synthetic inactivation inhibitors prolong the Na(+) current (I(Na)). The effects of Na(+) channel mutations on these pharmacological actions are incompletely investigated. Therefore, I compared the effects of inactivation inhibitors on I(Na) in WT or mutant (DeltaKPQ) human cardiac Na(+) channels expressed in HEK-293 cells, by measuring difference currents sensitive to 50muM tetrodotoxin. Veratridine and the pyrethroid tefluthrin prolonged I(Na) in WT and DeltaKPQ without obvious differential effects, while a sea anemone toxin (ATX-II) and a synthetic inotrope (SDZ 201-106) prolonged WT I(Na), but apparently blocked I(Na) in the DeltaKPQ mutant. This block was due, at least in-part, to enhanced steady-state inactivation, with half-inactivation potentials shifted by up to -17mV. Inactivation enhancement by ATX-II also persisted when conditioning depolarizations were abbreviated, and was unaffected by the additional presence of SDZ 201-106 consistent with these agents having unique interactions with DeltaKPQ Na(+) channels. It is concluded that the toxin-binding sites for ATX-II and SDZ 201-106 have allosteric effects converging on a common path affecting steady-state inactivation of DeltaKPQ I(Na). Pharmacological modulation of this path to increase inactivation in mutant Na(+) channels could potentially produce therapeutic benefits.
Spencer
C Ian
CI
Department of Pharmacological Sciences, CV Therapeutics Inc, 3172 Porter Drive, Palo Alto, CA 94304, USA. ian.spencer@fluxionbio.com
D000200:Action Potentials; D002316:Cardiotonic Agents / Q000494:pharmacology*; D002460:Cell Line; D003064:Cnidarian Venoms / Q000494:pharmacology*; D003521:Cyclopropanes / Q000494:pharmacology; D004594:Electrophysiology; D005786:Gene Expression Regulation / Q000502:physiology; D006801:Humans; D006845:Hydrocarbons, Fluorinated / Q000494:pharmacology; D015640:Ion Channel Gating / Q000187:drug effects*; D009124:Muscle Proteins / Q000235:genetics* / Q000378:metabolism*; D009154:Mutation; D062554:NAV1.5 Voltage-Gated Sodium Channel; D018408:Patch-Clamp Techniques; D010879:Piperazines / Q000494:pharmacology; D015222:Sodium Channels / Q000235:genetics* / Q000378:metabolism*; D014701:Veratridine / Q000494:pharmacology
D002316:Cardiotonic Agents; D003064:Cnidarian Venoms; D003521:Cyclopropanes; D006845:Hydrocarbons, Fluorinated; D009124:Muscle Proteins; D062554:NAV1.5 Voltage-Gated Sodium Channel; D010879:Piperazines; C568320:SCN5A protein, human; D015222:Sodium Channels; C489827:2,3,5,6-tetrafluoro-4-methylbenzyl (Z)-(1RS)-cis-3-(2-chloro-3,3,3-trifluoroprop-1-enyl)-2,2-dimethylcyclopropanecarboxylate; C028800:toxin II (Anemonia sulcata); D014701:Veratridine; C046261:DPI 201-106