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Related Experiment Videos

Saxitoxin blocks L-type ICa.

Zhi Su1, Michael Sheets, Hideyuki Ishida

  • 1Cardiology Division, University of Utah Health Sciences Center, Salt Lake City, Utah 84132, USA.

The Journal of Pharmacology and Experimental Therapeutics
|October 21, 2003
PubMed
Summary
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Saxitoxin (STX) inhibits L-type calcium channels, affecting heart cell calcium transients. This study reveals STX is not specific to sodium channels, impacting cardiac function research.

Area of Science:

  • Pharmacology
  • Cardiovascular Physiology
  • Ion Channel Biology

Background:

  • Saxitoxin (STX) and tetrodotoxin (TTX) are widely recognized as potent and selective blockers of voltage-gated sodium channels (Nav).
  • These toxins are crucial tools in electrophysiology for isolating and studying sodium channel function in various cell types, including cardiac myocytes.
  • The specificity of STX and TTX for sodium channels has been a foundational assumption in many physiological and pharmacological studies.

Purpose of the Study:

  • To investigate the potential off-target effects of commercial Saxitoxin (STX) on L-type calcium currents (I(Ca,L)).
  • To determine if STX, beyond its known action on sodium channels, impacts calcium handling in adult mouse ventricular myocytes (VMs).
  • To assess the specificity of STX and tetrodotoxin (TTX) on both sodium and calcium currents in cardiac and non-cardiac cells.

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Main Methods:

  • Electrophysiological recordings were performed on adult mouse ventricular myocytes (VMs) and tsA-201 cells co-transfected with calcium channel subunits.
  • Sodium currents (INa) and L-type calcium currents (I(Ca,L)) were measured using patch-clamp techniques with a rapid solution switching system.
  • Intracellular calcium concentration ([Ca2+]i) transients were monitored in single mouse VMs to assess functional calcium handling.

Main Results:

  • Saxitoxin (STX) at 10 microM completely blocked sodium currents (INa) in mouse VMs, confirming its known activity.
  • However, STX also significantly inhibited L-type calcium currents (I(Ca,L)) by 39% in mouse VMs and reduced intracellular calcium ([Ca2+]i) transients by 36%.
  • Tetrodotoxin (TTX) at 60 microM effectively blocked INa but showed minimal effect on I(Ca,L) and [Ca2+]i transients, highlighting a difference in specificity between STX and TTX.

Conclusions:

  • Commercial Saxitoxin (STX) exhibits inhibitory effects on L-type calcium currents (I(Ca,L)) in addition to its blockade of sodium channels.
  • The findings challenge the assumption of STX's complete specificity for sodium channels and suggest potential confounding effects in studies using this toxin.
  • Researchers should consider the non-specific actions of STX on calcium channels, particularly in cardiac cells, when interpreting experimental results.