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Single-channel pharmacology of mibefradil in human native T-type and recombinant Ca(v)3.2 calcium channels

Guido Michels1, Jan Matthes, Renate Handrock

  • 1Department of Pharmacology, University of Cologne, Cologne, Germany.

Molecular Pharmacology
|February 21, 2002
PubMed

Insights

This study characterized native human T-type calcium channels in medullary thyroid carcinoma cells, finding their mibefradil pharmacology matches recombinant Ca(v)3.2 channels. This provides molecular insights into T-type calcium channel function.

Area of Science:

  • Molecular Pharmacology
  • Ion Channel Biophysics
  • Cellular Physiology

Background:

  • Human medullary thyroid carcinoma (hMTC) cells express T-type currents and Ca(v)3.2 subunits.
  • Understanding low-voltage-activated calcium channels is crucial for cellular function.
  • Single-channel techniques allow detailed biophysical characterization.

Purpose of the Study:

  • To investigate the molecular pharmacology of low-voltage-activated calcium channels in hMTC cells.
  • To differentiate channel types based on biophysical properties and drug responses.
  • To compare native T-type channels with recombinant Ca(v)3.2 channels.

Main Methods:

  • Single-channel patch-clamp recording in hMTC cells.
  • Analysis of channel conductance, voltage dependence, inactivation kinetics, and gating.
  • Application of calcium agonist (S)-Bay K 8644 and T-type channel blocker mibefradil.
  • Comparison with recombinant Ca(v)3.2 channels expressed in HEK 293 cells.

Main Results:

  • Two distinct single-channel activities were observed: Type II (L-type) and Type I (T-type).
  • Type I channels exhibited low-voltage activation, small conductance (7.2 pS), rapid inactivation, and were insensitive to (S)-Bay K 8644.
  • Mibefradil inhibited Type I channels by reducing active sweeps and open-state duration, consistent with recombinant Ca(v)3.2 channel block.

Conclusions:

  • Native human T-type channels in hMTC cells possess a pharmacologic profile similar to recombinant Ca(v)3.2 channels.
  • Mibefradil effectively probes the pharmacologic phenotype of native T-type channels.
  • These findings enhance the understanding of T-type calcium channel molecular pharmacology.

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