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

Full Abstract

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).

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Author information

Author/s: Cai, Yidao (Y); Baxter, Douglas A (DA); Crow, Terry (T);

Affiliation: Department of Neurobiology and Anatomy, University of Texas at Houston Medical School, Houston, Texas 77030, USA. yidao.cai(-atsign-)uth.tmc.edu

Grants: P01 NS38310 (Agency:NINDS NIH HHS)

Journal and publication information

Publication Type: Journal Article; Research Support, U.S. Gov't, P.H.S.

Journal: Journal of computational neuroscience (J Comput Neurosci), published in United States. (Language: eng)

Reference: -2003 Jul-Aug; vol 15 (issue 1) : pp 105-21

Dates: Created 2003/07/04; Completed 2003/10/01; Revised 2008/11/21;

PMID: 12843698, status: MEDLINE (last retrieval date: 12/26/2008)

Sourced from the National Library of Medicine. Abstract text and other information may be subject to copyright.

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MeSH headings (categories)

This article was linked to the MESH Headings shown below.

Animals
Axons - physiology
Computer Simulation
Delayed Rectifier Potassium Channels
Humans
Mathematics
Membrane Potentials - physiology
Models, Neurological

Mollusca - physiology
Neurons - metabolism; physiology
Photoreceptor Cells, Invertebrate - metabolism; physiology
Potassium Channels - metabolism
Potassium Channels, Inwardly Rectifying - metabolism
Potassium Channels, Voltage-Gated
Reaction Time
Serotonin - metabolism

Associated Chemicals: Delayed Rectifier Potassium Channels (0) ; Potassium Channels (0) ; Potassium Channels, Inwardly Rectifying (0) ; Potassium Channels, Voltage-Gated (0) ; Serotonin (50-67-9)

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