Tetrodotoxin Sensitivity of the Vertebrate Cardiac Na + Current

• Main Authors: Matti Vornanen, Minna Hassinen, Jaakko Haverinen
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2011
• Subjects: Burbot
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.287.2413

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.