Reduction of spike frequency adaptation and blockade of M-current in rat CA1 pyramidal neurones by linopirdine (DuP 996), a neurotransmitter release enhancer

Br J Pharmacol. 1995 Aug;115(7):1163-8. doi: 10.1111/j.1476-5381.1995.tb15019.x.


1. Linopirdine (DuP 996) has been shown to enhance depolarization-induced release of several neurotransmitters in the CNS through a mechanism which may involve K+ channel blockade. The electrophysiological effects of linopirdine were therefore investigated directly, by use of conventional voltage recording and single electrode voltage-clamp. 2. Linopirdine (10 microM) reduced spike frequency adaptation (SFA) in rat hippocampal CA1 pyramidal neurones in vitro. The reduction of SFA comprised an increase in number of spikes and a reduction in inter-spike intervals after the first, but with no effect on time to first spike. Linopirdine also caused a voltage-dependent depolarization of resting membrane potential (RMP). 3. M-current (IM), a current known to underlie SFA and to set RMP, was blocked by linopirdine in a reversible, concentration-dependent manner (IC50 = 8.5 microM). This block was not reversed by atropine (10 microM). 4. Linopirdine did not affect IQ, the slow after-hyperpolarization following a spike train, or spike duration. 5. Linopirdine may represent a novel class of K+ blocker with relative selectivity for the M-current. This block of IM is consistent with the suggestion from a previous study that linopirdine may affect a tetraethylammonium-sensitive channel, and it could be speculated that IM blockade may be involved with the enhancement of neurotransmitter release by linopirdine.

MeSH terms

  • Action Potentials / drug effects
  • Adaptation, Physiological / drug effects
  • Animals
  • Indoles / pharmacology*
  • Ion Channel Gating / drug effects
  • Male
  • Neurotransmitter Agents / metabolism*
  • Potassium Channel Blockers
  • Pyramidal Cells / drug effects*
  • Pyramidal Cells / metabolism
  • Pyramidal Cells / physiology
  • Pyridines / pharmacology*
  • Rats


  • Indoles
  • Neurotransmitter Agents
  • Potassium Channel Blockers
  • Pyridines
  • linopirdine