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Related Experiment Videos

Molecular identification of a TTX-sensitive Ca(2+) current.

S Guatimosim1, E A Sobie, J dos Santos Cruz

  • 1Department of Physiology, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA.

American Journal of Physiology. Cell Physiology
|April 5, 2001
PubMed
Summary

The TTX-sensitive calcium current (I(Ca(TTX))) in cardiac cells is actually carried by cardiac sodium channels under sodium-free conditions. This current, proposed to be renamed I(Na(null)), allows calcium entry and exhibits unique properties.

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Area of Science:

  • Cardiovascular Physiology
  • Ion Channel Biophysics
  • Molecular Cardiology

Background:

  • Cardiac myocytes exhibit a TTX-sensitive calcium current (I(Ca(TTX))) under sodium-free conditions.
  • The molecular identity and ionic basis of this current have been debated.

Purpose of the Study:

  • To investigate the biophysical and molecular properties of I(Ca(TTX)) in cardiac myocytes.
  • To determine if cardiac sodium channels are responsible for I(Ca(TTX)).

Main Methods:

  • Patch-clamp electrophysiology
  • Calcium imaging in cardiac myocytes and HEK-293 cells expressing cardiac sodium channels
  • Ion substitution experiments (Cs(+), Ca(2+), TEA(+), NMDG(+))
  • Drug sensitivity assays (mibefradil)

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Main Results:

  • I(Ca(TTX)) is carried by Cs(+) and Ca(2+), but not TEA(+) or NMDG(+).
  • HEK-293 cells expressing cardiac sodium channels show a current with similar properties to I(Ca(TTX)).
  • I(Ca(TTX)) facilitates calcium influx, increasing intracellular calcium.
  • Ba(2+) did not permeate I(Ca(TTX)) under tested conditions.
  • Mibefradil blocked I(Ca(TTX)) and cardiac sodium current in transfected cells.

Conclusions:

  • I(Ca(TTX)) is mediated by cardiac sodium channels under sodium-free conditions.
  • The current should be renamed I(Na(null)) to reflect its molecular identity and activation conditions.
  • The findings contribute to understanding ion channel biophysics and permeation plasticity.