The Na+/Ca2+ exchange blocker SEA0400 fails to enhance cytosolic Ca2+ transient and contractility in canine ventricular cardiomyocytes

Cardiovasc Res. 2008 Jun 1;78(3):476-84. doi: 10.1093/cvr/cvn031. Epub 2008 Feb 5.


Aims: This study was designed to evaluate the effects of the Na(+)/Ca(2+) exchange (NCX) inhibitor SEA0400 on Ca(2+) handling in isolated canine ventricular myocytes.

Methods and results: Intracellular Ca(2+) ([Ca(2+)](i)) transients, induced by either field stimulation or caffeine flush, were monitored using Ca(2+) indicator dyes. [Ca(2+)](i)-dependent modulation of the inhibitory effect of SEA0400 on NCX was characterized by the changes in Ni(2+)-sensitive current in voltage-clamped myocytes. Sarcoplasmic reticulum (SR) Ca(2+) release and uptake were studied in SR membrane vesicles. Gating properties of single-ryanodine receptors were analysed in lipid bilayers. Ca(2+) sensitivity of the contractile machinery was evaluated in chemically skinned myocytes. In myocytes paced at 1 Hz, neither diastolic [Ca(2+)](i) nor the amplitude of [Ca(2+)](i) transients was significantly altered by SEA0400 up to the concentration of 1 microM, which was shown to inhibit the exchange current. The blocking effect of SEA0400 on NCX decreased with increasing [Ca(2+)](i), and it was more pronounced in reverse than in forward mode operation at every [Ca(2+)](i) examined. The rate of decay of the caffeine-induced [Ca(2+)](i) transients was decreased significantly by 1 microM SEA0400; however, this effect was only a fraction of that observed with 10 mM NiCl(2). Neither SR Ca(2+) release and uptake nor cell shortening and Ca(2+) sensitivity of the contractile proteins were influenced by SEA0400.

Conclusion: The lack of any major SEA0400-induced shift in Ca(2+) transients or contractility of myocytes can well be explained by its limited inhibitory effect on NCX (further attenuated by elevated [Ca(2+)](i) levels) and a concomitant reduction in Ca(2+) influx due to the predominantly reverse mode blockade of NCX and suppression of L-type Ca(2+) current.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aniline Compounds / pharmacology*
  • Animals
  • Caffeine / pharmacology
  • Calcium Channels, L-Type / metabolism
  • Calcium Signaling / drug effects*
  • Cardiac Pacing, Artificial
  • Cell Size / drug effects
  • Cytosol / metabolism
  • Dogs
  • Dose-Response Relationship, Drug
  • Female
  • In Vitro Techniques
  • Ion Channel Gating / drug effects
  • Male
  • Membrane Potentials
  • Myocardial Contraction / drug effects*
  • Myocytes, Cardiac / drug effects*
  • Myocytes, Cardiac / metabolism
  • Patch-Clamp Techniques
  • Phenyl Ethers / pharmacology*
  • Ryanodine Receptor Calcium Release Channel / drug effects
  • Ryanodine Receptor Calcium Release Channel / metabolism
  • Sarcoplasmic Reticulum / drug effects
  • Sarcoplasmic Reticulum / metabolism
  • Sodium-Calcium Exchanger / antagonists & inhibitors*
  • Sodium-Calcium Exchanger / metabolism
  • Time Factors


  • Aniline Compounds
  • Calcium Channels, L-Type
  • Phenyl Ethers
  • Ryanodine Receptor Calcium Release Channel
  • SEA 0400
  • Sodium-Calcium Exchanger
  • Caffeine