Enantioselective blockade of T-type Ca2+ current in adult rat sensory neurons by a steroid that lacks gamma-aminobutyric acid-modulatory activity

Mol Pharmacol. 1998 Nov;54(5):918-27. doi: 10.1124/mol.54.5.918.

Abstract

A number of steroids seem to have anesthetic effects resulting primarily from their ability to potentiate currents gated by gamma-aminobutyric acidA (GABAA) receptor activation. One such compound is (3alpha,5alpha, 17beta)-3-hydroxyandrostane-17-carbonitrile [(+)-ACN]. We were interested in whether carbonitrile substitution at other ring positions might result in other pharmacological consequences. Here we examine effects of (3beta,5alpha, 17beta)-17-hydroxyestrane-3-carbonitrile [(+)-ECN] on GABAA receptors and Ca2+ channels. In contrast to (+)-ACN, (+)-ECN does not potentiate GABAA-receptor activated currents, nor does it directly gate GABAA-receptor mediated currents. However, both steroids produce an enantioselective reduction of T-type current. (+)-ECN blocked T current with an IC50 value of 0.3 microM with a maximal block of 41%. (+)-ACN produced a partial block of T current (44% maximal block) with an IC50 value of 0.4 microM. Block of T current showed mild use- and voltage-dependence. The (-)-ECN enantiomer was about 33 times less potent than (+)-ECN, with an IC50 value of 10 microM and an amount of maximal block comparable to (+)-ECN. (+)-ECN was less effective at blocking high-voltage-activated Ca2+ current in DRG neurons (IC50 value of 9. 3 microM with maximal block of about 27%) and hippocampal neurons. (+)-ECN (10 microM) had minimal effects on voltage-gated sodium and potassium currents in rat chromaffin cells. The results identify a steroid with no effects on GABAA receptors that produces a partial inhibition of T-type Ca2+ current with reasonably high affinity and selectivity. Further study of steroid actions on T currents may lead to even more selective and potent agents.

Publication types

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

MeSH terms

  • Anesthetics / pharmacology
  • Animals
  • Calcium Channel Blockers / pharmacology*
  • Calcium Channels / classification
  • Calcium Channels / physiology*
  • Chromaffin Cells / drug effects
  • Chromaffin Cells / physiology
  • Estranes / pharmacology*
  • GABA Modulators / pharmacology*
  • Ganglia, Spinal / cytology
  • Ganglia, Spinal / drug effects
  • Hippocampus / cytology
  • Hippocampus / drug effects
  • Hippocampus / physiology
  • Kinetics
  • Male
  • Membrane Potentials / drug effects
  • Membrane Potentials / physiology
  • Neurons, Afferent / drug effects*
  • Neurons, Afferent / physiology*
  • Nitriles / pharmacology*
  • Potassium Channels / physiology
  • Pregnanediones / pharmacology
  • Rats
  • Rats, Sprague-Dawley
  • Receptors, GABA-A / drug effects
  • Receptors, GABA-A / physiology
  • Sodium Channels / physiology
  • Stereoisomerism

Substances

  • 17-hydroxyestrane-3-carbonitrile
  • Anesthetics
  • Calcium Channel Blockers
  • Calcium Channels
  • Estranes
  • GABA Modulators
  • Nitriles
  • Potassium Channels
  • Pregnanediones
  • Receptors, GABA-A
  • Sodium Channels
  • 3-hydroxy-5-estrane-17-carbonitrile
  • alphaxalone