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Frequency-dependent blockade of T-type Ca2+ current by efonidipine in cardiomyocytes

H Masumiya1, J Kase, Y Tanaka

  • 1Department of Pharmacology, Toho University School of Pharmaceutical Sciences, Funabashi, Chiba, Japan.

Life Sciences
|February 24, 2001
PubMed

Insights

Efonidipine, a calcium channel blocker, shows increased effectiveness in inhibiting T-type calcium channels at higher heart rates. This frequency-dependent action is attributed to the drug

Area of Science:

  • Cardiovascular Pharmacology
  • Ion Channel Physiology

Background:

  • Efonidipine is a dihydropyridine calcium (Ca2+) antagonist.
  • It inhibits both L-type and T-type Ca2+ channels.
  • Efonidipine exhibits bradycardiac activity, particularly in individuals with elevated heart rates.

Purpose of the Study:

  • To investigate the frequency-dependent effects of efonidipine on T-type Ca2+ channels.
  • To elucidate the mechanism behind efonidipine's action on T-type Ca2+ channels in cardiac myocytes.

Main Methods:

  • Isolated guinea-pig ventricular myocytes were utilized.
  • T-type Ca2+ currents were measured under varying stimulation frequencies (0.05 Hz, 0.2 Hz, 1 Hz).
  • Inhibition, inactivation, and recovery kinetics of T-type Ca2+ currents were analyzed.

Main Results:

  • Efonidipine's potency in inhibiting T-type Ca2+ current increased with higher stimulation frequencies.
  • IC50 values demonstrated a significant decrease at higher frequencies (1.3 x 10^-8 M at 1 Hz).
  • The drug slowed the recovery of T-type Ca2+ channels from inactivation, suggesting slow dissociation from the inactivated state.

Conclusions:

  • Efonidipine exhibits frequency-dependent inhibition of T-type Ca2+ channels.
  • This effect is likely due to slow drug dissociation from the channel's inactivated state.
  • The findings provide insights into the electrophysiological effects of efonidipine in cardiac tissue.

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