Contrasting biophysical and pharmacological properties of T-type and R-type calcium channels

Neuropharmacology. 1997 Jul;36(7):879-93. doi: 10.1016/s0028-3908(97)00086-5.


In contrast to other kinds of voltage-gated Ca2+ channels, the underlying molecular basis of T-type and R-type channels is not well-understood. To facilitate comparisons with cloned Ca2+ channel subunits, we have carried out a systematic analysis of the properties of T-type currents in undifferentiated NG108-15 cells and R-type currents in cerebellar granule neurons. Marked differences were found in their biophysical and pharmacological features under identical recording conditions. T-type channels became activated at potentials approximately 25 mV more negative than R-type channels; however, T-type channels required potentials approximately 15 mV less negative than R-type channels to be available. Accordingly, T-type channels display a much larger overlap between the curves describing inactivation and activation, making them more suitable for generating sustained Ca2+ entry in support of secretion or pacemaker activity. In contrast, R-type channels are not equipped to provide a steady current, but are very capable of supplying transient surges of Ca2+ influx. In response to a series of increasingly strong depolarizations T-type and R-type Ca2+ channels gave rise to very different kinetic patterns. T-type current records crossed each other in a characteristic pattern not found for R-type currents. These biophysical distinctions were independent of absolute membrane potential and were, therefore, complementary to the conventional categorization of T- and R-type Ca2+ channels as low- and high-voltage activated. R-type channels deactivated approximately eight-fold more quickly than T-type channels, with clear consequences for the generation of divalent cation influx during simulated action potentials. Pharmacological comparisons revealed additional contrasts. R-type current was responsive to block by omega-Aga IIIA but not nimodipine, while the opposite was true for T-type current. Both channel types were potently inhibited by the non-dihydropyridine compound mibefradil. In all respects examined, R-type currents were similar to currents derived from expression of the alpha1E subunit whereas T-type currents were not.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Benzimidazoles / pharmacology*
  • Biophysical Phenomena
  • Biophysics
  • Calcium Channel Blockers / pharmacology*
  • Calcium Channels / drug effects*
  • Calcium Channels / physiology*
  • Cells, Cultured
  • Cerebellum / drug effects
  • Mibefradil
  • Rats
  • Stereoisomerism
  • Tetrahydronaphthalenes / pharmacology*


  • Benzimidazoles
  • Calcium Channel Blockers
  • Calcium Channels
  • Tetrahydronaphthalenes
  • Mibefradil