Post-repolarization block of cloned sodium channels by saxitoxin

the contribution of pore-region amino acids

J. Satin, J. W. Kyle, Zheng Fan, R. Rogart, H. A. Fozzard, J. C. Makielski

Research output: Contribution to journalArticle

22 Citations (Scopus)

Abstract

Sodium channels expressed in oocytes exhibited isoform differences in phasic block by saxitoxin (STX). Neuronal channels (rat IIa co-expressed with beta 1 subunit, Br2a + beta 1) had slower kinetics of phasic block for pulse trains than cardiac channels (RHI). After the membrane was repolarized from a single brief depolarizing step, a test pulse at increasing intervals showed first a decrease in current (post-repolarization block) then eventual recovery in the presence of STX. This block/unblock process for Br2a + beta 1 was 10-fold slower than that for RHI. A model accounting for these results predicts a faster toxin dissociation rate and a slower association rate for the cardiac isoform, and it also predicts a shorter dwell time in a putative high STX affinity conformation for the cardiac isoform. The RHI mutation (Cys374-->Phe), which was previously shown to be neuronal-like with respect to high affinity tonic toxin block, was also neuronal-like with respect to the kinetics of post-repolarization block, suggesting that this single amino acid is important for conferring isoform-specific transition rates determining post-repolarization block. Because the same mutation determines both sensitivity for tonic STX block and the kinetics of phasic STX block, the mechanisms accounting for tonic block and phasic block share the same toxin binding site. We conclude that the residue at position 374, in the putative pore-forming region, confers isoform-specific channel kinetics that underlie phasic toxin block.

Original languageEnglish (US)
Pages (from-to)1353-1363
Number of pages11
JournalBiophysical Journal
Volume66
Issue number5
DOIs
StatePublished - Jan 1 1994

Fingerprint

Saxitoxin
Sodium Channels
Protein Isoforms
Amino Acids
Mutation
Exercise Test
Oocytes
Binding Sites
Membranes

All Science Journal Classification (ASJC) codes

  • Biophysics

Cite this

Post-repolarization block of cloned sodium channels by saxitoxin : the contribution of pore-region amino acids. / Satin, J.; Kyle, J. W.; Fan, Zheng; Rogart, R.; Fozzard, H. A.; Makielski, J. C.

In: Biophysical Journal, Vol. 66, No. 5, 01.01.1994, p. 1353-1363.

Research output: Contribution to journalArticle

Satin, J. ; Kyle, J. W. ; Fan, Zheng ; Rogart, R. ; Fozzard, H. A. ; Makielski, J. C. / Post-repolarization block of cloned sodium channels by saxitoxin : the contribution of pore-region amino acids. In: Biophysical Journal. 1994 ; Vol. 66, No. 5. pp. 1353-1363.
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