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 fo r investigating the critical interaction of light and turbulence stimuli wi thin the type B photoreceptor of Hermissenda crassicronis. The model includ es equations describing phototransduction, release of calcium from intracel lular stores, and other calcium regulatory mechanisms, as well as equations describing ligand-gating of a rhabdomeric sodium current. The model is use d to determine the sources of calcium in the soma, whether calcium or IP3 i s a plausible ligand of the light induced sodium current, and whether the l ight-induced potassium current is equivalent to the calcium-dependent potas sium current activated by light-induced calcium release. Simulations show t hat the early light-induced calcium elevation is due to influx through volt age-dependent channels, whereas the later calcium elevation is due to relea se from intracellular stores. Simulations suggest that the ligand of the fa st, light-induced sodium current is IP3 but that there is a smaller, prolon ged component of the light-induced sodium current that is activated by calc ium. In the model, the calcium-dependent potassium current, located in the soma, is activated only slightly by light-induced calcium elevation, leadin g to the prediction that a calcium-dependent potassium current, active at r esting potential, is located in the rhabdomere and is responsible for the l ight-induced potassium current.