Computational study of enhanced excitability in Hermissenda: membrane conductances modulated by 5-HT

J Comput Neurosci. 2003 Jul-Aug;15(1):105-21. doi: 10.1023/a:1024479020420.


Serotonin (5-HT) applied to the exposed but otherwise intact nervous system results in enhanced excitability of Hermissenda type-B photoreceptors. Several ion currents in the type-B photoreceptors are modulated by 5-HT, including the A-type K+ current (I(K,A)), sustained Ca2+ current (I(Ca,S)), Ca-dependent K+ current (I(K,Ca)), and a hyperpolarization-activated inward rectifier current (I(h)). In this study, we developed a computational model that reproduces physiological characteristics of type B photoreceptors, e.g. resting membrane potential, dark-adapted spike activity, spike width, and the amplitude difference between somatic and axonal spikes. We then used the model to investigate the contribution of different ion currents modulated by 5-HT to the magnitudes of enhanced excitability produced by 5-HT. Ion currents were systematically varied within limits observed experimentally, both individually and in combinations. A reduction of I(K,A) or I(K,Ca), or an increase in I(h) enhanced excitability by 20-50%. Decreasing I(Ca,S) produced a dramatic decrease in excitability. Reductions of I(K,V) produced only minimal increases in excitability, suggesting that I(K,V) probably plays a minor role in 5-HT induced enhanced excitability. Combinations of changes in I(K,A), I(K,Ca), I(h) and I(Ca,S) produced increases in excitability comparable to experimental observations. After 5-HT application, the cell's depolarization force is shifted from the I(h)-I(Ca,S) combination to predominantly I(h).

Publication types

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

MeSH terms

  • Animals
  • Axons / physiology
  • Computer Simulation
  • Delayed Rectifier Potassium Channels
  • Humans
  • Mathematics
  • Membrane Potentials / physiology*
  • Models, Neurological*
  • Mollusca / physiology*
  • Neurons / metabolism
  • Neurons / physiology*
  • Photoreceptor Cells, Invertebrate / metabolism
  • Photoreceptor Cells, Invertebrate / physiology*
  • Potassium Channels / metabolism
  • Potassium Channels, Inwardly Rectifying / metabolism
  • Potassium Channels, Voltage-Gated*
  • Reaction Time
  • Serotonin / metabolism*


  • Delayed Rectifier Potassium Channels
  • Potassium Channels
  • Potassium Channels, Inwardly Rectifying
  • Potassium Channels, Voltage-Gated
  • Serotonin