Characterization of the acetylcholine-induced potassium current in rabbit cardiac Purkinje fibres

J Physiol. 1986 Feb;371:219-37. doi: 10.1113/jphysiol.1986.sp015970.

Abstract

Acetylcholine (ACh) induces a K+ current in rabbit cardiac Purkinje fibres. The question was studied whether ACh produces this effect by modifying the properties of K+ channels pre-existing in the absence of the neurotransmitter or whether it induces the formation of a different type of K+ channels. The relaxation properties of the ACh-induced current and its blockade by Cs+ and Ba2+ have been investigated using voltage clamp. During hyperpolarizing or depolarizing voltage pulses of moderate amplitude, the ACh-induced current is time independent. For large voltage pulses, time-dependent changes of the ACh-induced current are observed. These latter changes can be explained by intracellular K+ accumulation/depletion phenomena or by the effects of ACh on time-dependent currents (e.g. the late outward current, ix). Cs+ and Ba2+ block the ACh-induced current. The block produced by 20 mM-Cs+ is instantaneous and increases with hyperpolarization, i.e. it is voltage dependent. The block produced by Ba2+ at high concentrations (greater than 1 mM) is also instantaneous but complete at all potentials studied, and thus voltage independent. At these concentrations, either ion also blocks the background inward rectifier (iK1) current in a similar way. Low [Ba2+] (less than 0.1 mM) cause a block of the ACh-induced current which is instantaneous and little voltage dependent. The block of iK1 in contrast is time and voltage dependent for the same concentrations. These results indicate that the ACh-induced K+ current is different from the background iK1 current.

MeSH terms

  • Acetylcholine / pharmacology*
  • Action Potentials / drug effects
  • Animals
  • Barium / pharmacology
  • Cesium / pharmacology
  • Heart Conduction System / physiology*
  • In Vitro Techniques
  • Ion Channels / drug effects*
  • Models, Biological
  • Potassium / physiology*
  • Purkinje Fibers / physiology*
  • Rabbits
  • Time Factors

Substances

  • Ion Channels
  • Cesium
  • Barium
  • Acetylcholine
  • Potassium