The properties of batrachotoxin-modified cardiac Na channels, including state-dependent block by tetrodotoxin

Li-Yen Huang, A. Yatani, A. M. Brown

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Abstract

Batrachotoxin (BTX) modification and tetrodotoxin (TTX) block of BTX-modified Na channels were studied in single cardiac cells of neonatal rats using the whole-cell patch-clamp recording technique. The properties of BTX-modified Na channels in heart are qualitatively similar to those in nerve. However, quantitative differences do exist between the modified channels of these two tissues. In the heart, the shift of the conductance-voltage curve for the modified channel was less pronounced, the maximal activation rate constant, (τ(m))(max), of modified channels was considerably slower, and the slow inactivation of the BTX-modified cardiac Na channels was only partially abolished. TTX blocked BTX-modified mammalian cardiac Na channels and the block decreased over the potential range of -80 to -40 mV. The apparent dissociation constant of TTX changed from 0.23 μM at -50 mV to 0.69 μM at 0 mV. No further reduction of block was observed at potentials greater than -40 mV. This is the potential range over which gating from closed to open states occurred. These results were explained by assuming that TTX has a higher affinity for closed BTX-modified channels than for open modified channels. Hence, the TTX-binding rate constants are considered to be state dependent rather than voltage dependent. This differs from the voltage dependence of TTX block reported for BTX-modified Na channels from membrane vesicles incorporated into lipid bilayers and from amphibian node of Ranvier.

Original languageEnglish (US)
Pages (from-to)341-360
Number of pages20
JournalJournal of General Physiology
Volume90
Issue number3
StatePublished - 1987

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Batrachotoxins
Tetrodotoxin
Ranvier's Nodes
Lipid Bilayers
Amphibians
Patch-Clamp Techniques
Ion Channels

ASJC Scopus subject areas

  • Physiology

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The properties of batrachotoxin-modified cardiac Na channels, including state-dependent block by tetrodotoxin. / Huang, Li-Yen; Yatani, A.; Brown, A. M.

In: Journal of General Physiology, Vol. 90, No. 3, 1987, p. 341-360.

Research output: Contribution to journalArticle

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