Mechanisms of verapamil inhibition of action potential firing in rat intracardiac ganglion neurons

J Pharmacol Exp Ther. 1999 Jun;289(3):1502-8.

Abstract

The effects of verapamil and related phenylalkylamines on neuronal excitability were investigated in isolated neurons of rat intracardiac ganglia using whole-cell perforated patch-clamp recording. Verapamil (>/=10 microM) inhibits tonic firing observed in response to depolarizing current pulses at 22 degrees C. The inhibition of discharge activity is not due to block of voltage-dependent Ca2+ channels because firing is not affected by 100 microM Cd2+. The K+ channel inhibitors charybdotoxin (100 nM), 4-aminopyridine (0.5 mM), apamin (30-100 nM), and tetraethylammonium ions (1 mM) also have no effect on firing behavior at 22 degrees C. Verapamil does not antagonize the acetylcholine-induced inhibition of the muscarine-sensitive K+ current (M-current) in rat intracardiac neurons. Verapamil inhibits the delayed outwardly rectifying K+ current with an IC50 value of 11 microM, which is approximately 7-fold more potent than its inhibition of high voltage-activated Ca2+ channel currents. These data suggest that verapamil inhibits tonic firing in rat intracardiac neurons primarily via inhibition of delayed outwardly rectifying K+ current. Verapamil inhibition of action potential firing in intracardiac neurons may contribute, in part, to verapamil-induced tachycardia.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 4-Aminopyridine / pharmacology
  • Acetylcholine / pharmacology
  • Action Potentials / drug effects*
  • Animals
  • Animals, Newborn
  • Apamin / pharmacology
  • Cells, Cultured
  • Charybdotoxin / pharmacology
  • Electric Stimulation
  • Ganglia, Parasympathetic / physiology*
  • Heart / innervation*
  • Membrane Potentials / drug effects
  • Muscarine / pharmacology
  • Neurons / drug effects
  • Neurons / physiology*
  • Patch-Clamp Techniques
  • Potassium Channel Blockers
  • Potassium Channels / physiology
  • Rats
  • Tetraethylammonium / pharmacology
  • Verapamil / pharmacology*

Substances

  • Potassium Channel Blockers
  • Potassium Channels
  • Charybdotoxin
  • Apamin
  • Tetraethylammonium
  • Muscarine
  • 4-Aminopyridine
  • Verapamil
  • Acetylcholine