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Mar. Drugs 2011, 9(11), 2409-2422; doi:10.3390/md9112409
Article

Tetrodotoxin Sensitivity of the Vertebrate Cardiac Na+ Current

* ,
 and
Department of Biology, University of Eastern Finland, Joensuu 80101, Finland
* Author to whom correspondence should be addressed.
Received: 20 September 2011 / Revised: 2 November 2011 / Accepted: 10 November 2011 / Published: 21 November 2011
(This article belongs to the Special Issue Tetrodotoxin)
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Abstract

Evolutionary origin and physiological significance of the tetrodotoxin (TTX) resistance of the vertebrate cardiac Na+ current (INa) is still unresolved. To this end, TTX sensitivity of the cardiac INa was examined in cardiac myocytes of a cyclostome (lamprey), three teleost fishes (crucian carp, burbot and rainbow trout), a clawed frog, a snake (viper) and a bird (quail). In lamprey, teleost fishes, frog and bird the cardiac INa was highly TTX-sensitive with EC50-values between 1.4 and 6.6 nmol·L−1. In the snake heart, about 80% of the INa was TTX-resistant with EC50 value of 0.65 μmol·L−1, the rest being TTX-sensitive (EC50 = 0.5 nmol·L−1). Although TTX-resistance of the cardiac INa appears to be limited to mammals and reptiles, the presence of TTX-resistant isoform of Na+ channel in the lamprey heart suggest an early evolutionary origin of the TTX-resistance, perhaps in the common ancestor of all vertebrates.
Keywords: evolution of tetrodotoxin sensitivity; vertebrate animals; cardiac sodium current evolution of tetrodotoxin sensitivity; vertebrate animals; cardiac sodium current
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).
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Vornanen, M.; Hassinen, M.; Haverinen, J. Tetrodotoxin Sensitivity of the Vertebrate Cardiac Na+ Current. Mar. Drugs 2011, 9, 2409-2422.

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