Alpha-drenergic inhibition of calcium-dependent potentials in rat sympathetic neurones

J Physiol. 1980 Apr;301:191-204. doi: 10.1113/jphysiol.1980.sp013198.

Abstract

1. Post-ganglionic neurones of the rat superior cervical ganglion were studied in vitro (21-26 degrees C) using single intracellular micro-electrode methods. 2. Three Ca2+-dependent potentials were studied: the shoulder on the normal action potential, the hyperpolarizing afterpotential (h.a.p.), and th Ca2+ spike. 3. Bath-applied noradrenaline reversibly inhibited these Ca2+-dependent potentials. The EC50 for inhibition of peak h.a.p. amplitude was about 1 microM. The order of catetholamine potency was: L-adrenaline > L-noradrenaline > D-noradrenaline congruent to dopamine > DL-isoprenaline. Phentolamine (10 microM), an alpha-blocker, but not MJ-1999 (10 microM), a beta-blocker, antagonized the action of noradrenaline. 4. Noradrenaline (10 microM) hyperpolarized most neurones (1-6 mV) studied, with no detectable change in resting membrane conductance. 5. Superfusion with low external Ca2+ and high Mg2+ mimicked the effect of noradrenaline. Either procedure alone antagonized the h.a.p. conductance increase but did not alter the h.a.p. reversal potential. However, in the presence of low Ca2+, high Mg2+, the remaining action potential and h.a.p. were not further reduced by noradrenaline. 6. The Ca2+-dependent shoulder of the action potential did not appear dependent upon GK. Noradrenaline and low Ca2+ antagonized the shoulder when enhanced by TEA+ or Ba2+. 7. Both the rate of rise and amplitude of the Ca2+ spike were antagonized by noradrenaline. 8. We propose that activation of an alpha-adrenoceptor inhibits a voltage-sensitive Ca2+ conductance (GCa(V)), thereby reducing the inward Ca2+ current which may generate the noraml action potential shoulder and the rising phase of the Ca2+ spike. Reduction of Ca2+ current would also reduce the Ca2+-dependent portion of outward K+ current underlying the h.a.p.

Publication types

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

MeSH terms

  • Animals
  • Autonomic Fibers, Postganglionic / physiology*
  • Barium / pharmacology
  • Calcium / physiology*
  • Dopamine / pharmacology
  • Dose-Response Relationship, Drug
  • Electric Conductivity
  • Epinephrine / pharmacology*
  • Ganglia, Sympathetic / physiology*
  • In Vitro Techniques
  • Isoproterenol / pharmacology
  • Membrane Potentials / drug effects
  • Phentolamine / pharmacology
  • Rats
  • Receptors, Adrenergic / physiology*
  • Receptors, Adrenergic, alpha / physiology*
  • Tetraethylammonium Compounds / pharmacology
  • Tetrodotoxin / pharmacology

Substances

  • Receptors, Adrenergic
  • Receptors, Adrenergic, alpha
  • Tetraethylammonium Compounds
  • Barium
  • Tetrodotoxin
  • Isoproterenol
  • Calcium
  • Dopamine
  • Epinephrine
  • Phentolamine