Computational Study of Enhanced Excitability in Hermissenda: Membrane Conductances Modulated by 5-HT
Tóm tắt
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 (IK,A), sustained Ca2+ current (ICa,S), Ca-dependent K+ current (IK,Ca), and a hyperpolarization-activated inward rectifier current (Ih). 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 IK,A or IK,Ca, or an increase in Ih enhanced excitability by 20–50%. Decreasing ICa,S produced a dramatic decrease in excitability. Reductions of IK,V produced only minimal increases in excitability, suggesting that IK,V probably plays a minor role in 5-HT induced enhanced excitability. Combinations of changes in IK,A, IK,Ca, Ih and ICa,S produced increases in excitability comparable to experimental observations. After 5-HT application, the cell's depolarization force is shifted from the Ih–ICa,S combination to predominantly Ih.
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