Evidence for a distinct light-induced calcium-dependent potassium current in Hermissenda crassicornis.
A model of phototransduction is developed as a first step toward a model for investigating the critical interaction of light and turbulence stimuli within the type B photoreceptor of Hermissenda crassicronis. The model includes equations describing phototransduction, release of calcium from intracellular stores, and other calcium regulatory mechanisms, as well as equations describing ligand-gating of a rhabdomeric sodium current. The model is used to determine the sources of calcium in the soma, whether calcium or IP3 is a plausible ligand of the light-induced sodium current, and whether the light-induced potassium current is equivalent to the calcium-dependent potassium current activated by light-induced calcium release. Simulations show that the early light-induced calcium elevation is due to influx through voltage-dependent channels, whereas the later calcium elevation is due to release from intracellular stores. Simulations suggest that the ligand of the fast, light-induced sodium current is IP3 but that there is a smaller, prolonged component of the light-induced sodium current that is activated by calcium. In the model, the calcium-dependent potassium current, located in the soma, is activated only slightly by light-induced calcium elevation, leading to the prediction that a calcium-dependent potassium current, active at resting potential, is located in the rhabdomere and is responsible for the light-induced potassium current.
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Institute for Computational Sciences and Informatics, and Krasnow Institute for Advanced Study, George Mason University, Fairfax, VA 22030, USA. avrama@gmu.edu
D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D023421:Models, Animal; D008959:Models, Neurological; D008974:Mollusca / Q000033:anatomy & histology / Q000502:physiology*; D010775:Photic Stimulation; D017956:Photoreceptor Cells, Invertebrate / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism; D014785:Vision, Ocular / Q000187:drug effects / Q000502:physiology*
D015221:Potassium Channels; D015222:Sodium Channels; D002118:Calcium