title: Contribution of the late sodium current to intracellular sodium and calcium overload in rabbit ventricular myocytes treated by anemone toxin.
abstract: Pathological enhancement of late Na(+) current (INa) can potentially modify intracellular ion homeostasis and contribute to cardiac dysfunction. We tested the hypothesis that modulation of late INa can be a source of intracellular Na(+) ([Na(+)]i) overload. Late INa was enhanced by exposing rabbit ventricular myocytes to Anemonia sulcata toxin II (ATX-II) and measured using whole cell patch-clamp technique. [Na(+)]i was determined with fluorescent dye Asante NaTRIUM Green-2 AM. Pacing-induced changes in the dye fluorescence measured at 37°C were more pronounced in ATX-II-treated cells than in control (dye washout prevented calibration). At 22-24°C, resting [Na(+)]i was 6.6 ± 0.8 mM. Treatment with 5 nM ATX-II increased late INa 8.7-fold. [Na(+)]i measured after 2 min of electrical stimulation (1 Hz) was 10.8 ± 1.5 mM and 22.1 ± 1.6 mM (P < 0.001) in the absence and presence of 5 nM ATX-II, respectively. Inhibition of late INa with GS-967 (1 μM) prevented Na(+) i accumulation. A strong positive correlation was observed between the late INa and the pacing-induced increase of [Na(+)]i (R(2) = 0.88) and between the rise in [Na(+)]i and the increases in cytosolic Ca(2+) (R(2) = 0.96). ATX-II, tetrodotoxin, or GS-967 did not affect [Na(+)]i in quiescent myocytes suggesting that late INa was solely responsible for triggering the ATX-II effect on [Na(+)]i. Experiments with pinacidil and E4031 indicate that prolongation of the action potential contributes to as much as 50% of the [Na(+)]i overload associated with the increase in late INa caused by ATX-II. Enhancement of late INa can cause intracellular Na(+) overload in ventricular myocytes.
authors.affiliation: Department of Biology, Gilead Sciences Inc., Foster City, California dmytro.kornyeyev@gilead.com.
authors.forename: Dmytro
authors.initials: D
authors.lastname: Kornyeyev
authors.affiliation: Department of Biology, Gilead Sciences Inc., Foster City, California.
authors.forename: Nesrine
authors.initials: N
authors.lastname: El-Bizri
authors.affiliation: Department of Biology, Gilead Sciences Inc., Foster City, California.
authors.forename: Ryoko
authors.initials: R
authors.lastname: Hirakawa
authors.affiliation: Department of Biology, Gilead Sciences Inc., Foster City, California.
authors.forename: Steven
authors.initials: S
authors.lastname: Nguyen
authors.affiliation: Department of Biology, Gilead Sciences Inc., Foster City, California.
authors.forename: Serge
authors.initials: S
authors.lastname: Viatchenko-Karpinski
authors.affiliation: Department of Biology, Gilead Sciences Inc., Foster City, California.
authors.forename: Lina
authors.initials: L
authors.lastname: Yao
authors.affiliation: Department of Biology, Gilead Sciences Inc., Foster City, California.
authors.forename: Sridharan
authors.initials: S
authors.lastname: Rajamani
authors.affiliation: Department of Biology, Gilead Sciences Inc., Foster City, California.
authors.forename: Luiz
authors.initials: L
authors.lastname: Belardinelli
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002316:Cardiotonic Agents / Q000494:pharmacology*; D003064:Cnidarian Venoms / Q000494:pharmacology*; D049452:Green Fluorescent Proteins; D006352:Heart Ventricles / Q000166:cytology; D007211:Indoles; D032383:Myocytes, Cardiac / Q000187:drug effects* / Q000378:metabolism; D061848:Optical Imaging; D018408:Patch-Clamp Techniques; D011817:Rabbits; D012964:Sodium / Q000378:metabolism*; D015222:Sodium Channels / Q000187:drug effects* / Q000378:metabolism
chemical_list: D002316:Cardiotonic Agents; D003064:Cnidarian Venoms; D007211:Indoles; D015222:Sodium Channels; C059587:Indo-1 pentaacetoxymethyl ester; D049452:Green Fluorescent Proteins; C028800:toxin II (Anemonia sulcata); D012964:Sodium; D002118:Calcium
keywords: E-C coupling; anemone toxin; calcium; ion channels; sodium