On the potassium conductance increased by opioids in rat locus coeruleus neurones

J Physiol. 1985 Jul;364:265-80. doi: 10.1113/jphysiol.1985.sp015743.

Abstract

Intracellular recordings were made from locus coeruleus neurones in slices cut from rat pons and superfused in vitro. Membrane currents were recorded with a single-electrode switch-clamp amplifier. Opioids, enkephalin analogues or morphine, caused a concentration-dependent potassium current, which had a maximum value of about 300 pA at -60 mV. The opioid-sensitive potassium conductance was independent of membrane potential between -60 and -130 mV, but became less as the membrane potential was changed from -60 to -30 mV. The opioid outward current was reduced by quinine (100 microM-1 mM) and barium (30 microM-2 mM), but not by 4-aminopyridine (100 microM-1 mM) or tetraethylammonium (10 mM). A potassium current with similar properties flowed for several seconds after a burst of action potentials; this appeared to result from calcium entering the neurone during the action potentials. The alpha 2-adrenoceptor agonists noradrenaline and clonidine caused a concentration-dependent potassium conductance increase which had the same maximum value as that caused by opioids in the same neurones. Experiments in which an opioid and an alpha 2-adrenoceptor agonist were superfused together indicated that the same potassium conductance is increased by both agonists.

Publication types

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

MeSH terms

  • Action Potentials / drug effects
  • Animals
  • Clonidine / pharmacology
  • Endorphins / pharmacology*
  • Enkephalin, Methionine / pharmacology
  • In Vitro Techniques
  • Ion Channels / drug effects
  • Locus Coeruleus / cytology*
  • Morphine Derivatives / pharmacology
  • Neurons / physiology*
  • Norepinephrine / pharmacology
  • Potassium / physiology*
  • Quinine / pharmacology
  • Rats
  • Tetraethylammonium
  • Tetraethylammonium Compounds / pharmacology

Substances

  • Endorphins
  • Ion Channels
  • Morphine Derivatives
  • Tetraethylammonium Compounds
  • Enkephalin, Methionine
  • Tetraethylammonium
  • Quinine
  • Clonidine
  • Potassium
  • Norepinephrine
  • normorphine