Tetrodotoxin blockade on canine cardiac L-type Ca2+ channels depends on pH and redox potential

Bence Hegyi, I. Komáromi, Kornél Kistamás, Ferenc Ruzsnavszky, Krisztina Váczi, Balázs Horváth, J. Magyar, Tamás Bányász, P. Nánási, N. Szentandrássy

Research output: Contribution to journalArticle

5 Citations (Scopus)

Abstract

Tetrodotoxin (TTX) is believed to be one of the most selective inhibitors of voltage-gated fast Na+ channels in excitable tissues. Recently, however, TTX has been shown to block L-type Ca2+ current (I Ca) in canine cardiac cells. In the present study, the TTX-sensitivity of ICa was studied in isolated canine ventricular myocytes as a function of (1) channel phosphorylation, (2) extracellular pH and (3) the redox potential of the bathing medium using the whole cell voltage clamp technique. Fifty-five micromoles of TTX (IC50 value obtained under physiological conditions) caused 60% ± 2% inhibition of ICa in acidic (pH = 6.4), while only a 26% ± 2% block in alkaline (pH = 8.4) milieu. Similarly, the same concentration of TTX induced 62% ± 6% suppression of ICa in a reductant milieu (containing glutathione + ascorbic acid + dithiothreitol, 1 mM each), in contrast to the 31% ± 3% blockade obtained in the presence of a strong oxidant (100 μM H 2O2). Phosphorylation of the channel protein (induced by 3 μM forskolin) failed to modify the inhibiting potency of TTX; an IC 50 value of 50 ± 4 μM was found in forskolin. The results are in a good accordance with the predictions of our model, indicating that TTX binds, in fact, to the selectivity filter of cardiac L-type Ca channels.

Original languageEnglish
Pages (from-to)2140-2153
Number of pages14
JournalMarine Drugs
Volume11
Issue number6
DOIs
Publication statusPublished - Jun 2013

Fingerprint

Tetrodotoxin
Oxidation-Reduction
Canidae
Colforsin
Phosphorylation
Dithiothreitol
Reducing Agents
Patch-Clamp Techniques
Oxidants
Muscle Cells
Ascorbic Acid
Inhibitory Concentration 50
Glutathione
Proteins

Keywords

  • Calcium current
  • Dog heart
  • pH dependence
  • Redox potential
  • Tetrodotoxin

ASJC Scopus subject areas

  • Drug Discovery

Cite this

Tetrodotoxin blockade on canine cardiac L-type Ca2+ channels depends on pH and redox potential. / Hegyi, Bence; Komáromi, I.; Kistamás, Kornél; Ruzsnavszky, Ferenc; Váczi, Krisztina; Horváth, Balázs; Magyar, J.; Bányász, Tamás; Nánási, P.; Szentandrássy, N.

In: Marine Drugs, Vol. 11, No. 6, 06.2013, p. 2140-2153.

Research output: Contribution to journalArticle

Hegyi, Bence ; Komáromi, I. ; Kistamás, Kornél ; Ruzsnavszky, Ferenc ; Váczi, Krisztina ; Horváth, Balázs ; Magyar, J. ; Bányász, Tamás ; Nánási, P. ; Szentandrássy, N. / Tetrodotoxin blockade on canine cardiac L-type Ca2+ channels depends on pH and redox potential. In: Marine Drugs. 2013 ; Vol. 11, No. 6. pp. 2140-2153.
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AU - Komáromi, I.

AU - Kistamás, Kornél

AU - Ruzsnavszky, Ferenc

AU - Váczi, Krisztina

AU - Horváth, Balázs

AU - Magyar, J.

AU - Bányász, Tamás

AU - Nánási, P.

AU - Szentandrássy, N.

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N2 - Tetrodotoxin (TTX) is believed to be one of the most selective inhibitors of voltage-gated fast Na+ channels in excitable tissues. Recently, however, TTX has been shown to block L-type Ca2+ current (I Ca) in canine cardiac cells. In the present study, the TTX-sensitivity of ICa was studied in isolated canine ventricular myocytes as a function of (1) channel phosphorylation, (2) extracellular pH and (3) the redox potential of the bathing medium using the whole cell voltage clamp technique. Fifty-five micromoles of TTX (IC50 value obtained under physiological conditions) caused 60% ± 2% inhibition of ICa in acidic (pH = 6.4), while only a 26% ± 2% block in alkaline (pH = 8.4) milieu. Similarly, the same concentration of TTX induced 62% ± 6% suppression of ICa in a reductant milieu (containing glutathione + ascorbic acid + dithiothreitol, 1 mM each), in contrast to the 31% ± 3% blockade obtained in the presence of a strong oxidant (100 μM H 2O2). Phosphorylation of the channel protein (induced by 3 μM forskolin) failed to modify the inhibiting potency of TTX; an IC 50 value of 50 ± 4 μM was found in forskolin. The results are in a good accordance with the predictions of our model, indicating that TTX binds, in fact, to the selectivity filter of cardiac L-type Ca channels.

AB - Tetrodotoxin (TTX) is believed to be one of the most selective inhibitors of voltage-gated fast Na+ channels in excitable tissues. Recently, however, TTX has been shown to block L-type Ca2+ current (I Ca) in canine cardiac cells. In the present study, the TTX-sensitivity of ICa was studied in isolated canine ventricular myocytes as a function of (1) channel phosphorylation, (2) extracellular pH and (3) the redox potential of the bathing medium using the whole cell voltage clamp technique. Fifty-five micromoles of TTX (IC50 value obtained under physiological conditions) caused 60% ± 2% inhibition of ICa in acidic (pH = 6.4), while only a 26% ± 2% block in alkaline (pH = 8.4) milieu. Similarly, the same concentration of TTX induced 62% ± 6% suppression of ICa in a reductant milieu (containing glutathione + ascorbic acid + dithiothreitol, 1 mM each), in contrast to the 31% ± 3% blockade obtained in the presence of a strong oxidant (100 μM H 2O2). Phosphorylation of the channel protein (induced by 3 μM forskolin) failed to modify the inhibiting potency of TTX; an IC 50 value of 50 ± 4 μM was found in forskolin. The results are in a good accordance with the predictions of our model, indicating that TTX binds, in fact, to the selectivity filter of cardiac L-type Ca channels.

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KW - Dog heart

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KW - Redox potential

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