Cyclic AMP modulates electrical signaling in a weakly electric fish

J Comp Physiol A Neuroethol Sens Neural Behav Physiol. 2003 Apr;189(4):273-82. doi: 10.1007/s00359-003-0400-8. Epub 2003 Mar 13.

Abstract

Many species of electric fish show diurnal or socially elicited variation in electric organ discharge amplitude. In Sternopygus macrurus, activation of protein kinase A by 8-bromo-cAMP increases electrocyte sodium current magnitude. To determine whether the behavioral plasticity in electric organ discharge amplitude is controlled by electrocyte biophysical properties, we examined whether the effects of phosphorylation on ion currents in the electric organ translate directly into electric organ discharge changes. We injected the electric organ of restrained fish with 8-bromo-cAMP and monitored the electric organ discharge. The effect of protein kinase A activation on electrocyte action potentials was examined in isolated electric organ using two-electrode current clamp. Electric organ discharge and action potential amplitude and pulse duration increased in response to 8-bromo-cAMP. Pulse and action potential duration both increased by about 25%. However, the increase in electric organ discharge amplitude (approximately 400%) was several-fold greater than the action potential amplitude increase (approximately 40%). Resting membrane resistance decreased in electrocytes exposed to 8-bromo-cAMP. We propose that in the Thevenin equivalent circuit of the electric organ a moderate increase in action potential amplitude combined with a decrease in internal resistance produces a greater voltage drop across the external resistance (the water around the fish), accounting for the large increase in the externally recorded electric organ discharge.

Publication types

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

MeSH terms

  • 8-Bromo Cyclic Adenosine Monophosphate / pharmacology*
  • Action Potentials / drug effects*
  • Action Potentials / physiology*
  • Animals
  • Cyclic AMP / pharmacology
  • Electric Fish / physiology
  • Electric Organ / drug effects*
  • Electric Organ / physiology*
  • In Vitro Techniques
  • Neurons / drug effects
  • Neurons / physiology
  • Patch-Clamp Techniques
  • Reproducibility of Results
  • Sensitivity and Specificity
  • Sodium Channels / drug effects
  • Sodium Chloride / pharmacology

Substances

  • Sodium Channels
  • 8-Bromo Cyclic Adenosine Monophosphate
  • Sodium Chloride
  • Cyclic AMP